Piezoelectric ceramics such as PbZr1-xTixO3 (PZT) show enhanced electro-mechanical properties at morphotropic phase boundary (MPB) separating two ferroelectric polar phases in the compositional phase diagram. Designing MPB in Pb-free perovskite oxide is challenging due to the lack of suitable polar tetragonal oxide with high Curie temperature. In this study, we explored the BiFeO3 – Bi0.5K0.5TiO3 – BaTiO3 ternary phase diagram and searched for Bi-rich perovskite oxides as candidates for piezoceramics near MPB. The phase diagram offers a Bi-rich polar tetragonal (T[001]) phase [0.75BaTiO3–0.25(K0.5Bi0.5)TiO3] and a well-known rhombohedral (R[111]) phase BiFeO3. A solid solution is observed in the entire range between the T[001] phase and the R[111] phase. Structural investigation through powder diffraction and Raman spectroscopy studies suggests the existence of a complex region (MPB), well separated by the rhombohedral and tetragonal phases. The composition (Bi0.670K0.050Ba0.280)(Fe0.62Ti0.38)O3 at the MPB shows a large signal piezoelectric coefficient of d33* = 41.5 pm/V at room temperature.

The double perovskite Eu2CoMnO6 (ECMO), known for its complicated metamagnetic behavior, was studied in this report to examine how postannealing synthesis affects its crystal structure and magnetic and electronic behavior. The slow-cooling, Argon treatment, and quenching procedure during the sample synthesis indicated the important significance of antisite disorder (ASD) in influencing the material’s magnetic response. The magnetic study revealed diverse transitions, including two low-temperature antiferromagnetic (AFM)-like transitions at ∼51 and ∼10 K in the slow-cooled sample and vibronic ferromagnetic (FM) superexchange interactions at ∼105 K in the argon (Ar)-treated sample, while the quenched sample displayed an AFM behavior at low temperatures. The XPS analysis indicated the presence of diverse concentrations of Co and Mn in multiple valence states, specifically (2+, 3+) and (3+, 4+) respectively, across the samples subjected to different annealing processes. The Griffiths phase was particularly noticeable in the quenched sample, highlighting the role of disorder with Griffith’s disorder exponent (λ) = 0.81. The M(H) data at 2.5 K under zero-field-cooled mode revealed that the Ar-treated sample had a smooth, saturating-like loop, while the quenched sample had the hysteresis loop shifted toward the positive field axis with a reduced magnetic moment of 2.2 μB/f.u., and the slow-cooled sample exhibited sharp metamagnetic jumps with an unsaturated magnetic moment of 3.3 μB/f.u. While M(H) data recorded under a field-cooled protocol altered the position of critical fields (HC) for the slow-cooled sample, the evolution of an extra magnetization jump was noticed in the case of the Ar-annealed sample, and the quenched sample showed the loop shifting completely toward the negative field axis. The loop shift and varying HC values were explained in terms of an exchange bias-like spin-pinning mechanism. Additionally, DFT calculations corroborate the experimental results, revealing an increased likelihood of antisite disorders in the presence of oxygen vacancies, as well as altered behavior of Co and Mn spin states in relation to the disorders and oxygen vacancies. The effect of the disorder and oxygen vacancies on the electrical and magnetic ground states was also investigated, and the results were complemented with the experimentally observed magnetic behavior. This study demonstrates how postannealing conditions may be carefully controlled to regulate the disorder and, thus, magnetic behavior, including valence states, Griffiths phase, and metamagnetic behavior of ECMO, opening up new avenues for developing materials with desired functional properties.

Ferroelectric polymers are highly promising electroactive materials, renowned for their exceptional properties that make them ideal for various flexible electronic devices. Polyvinylidene fluoride (PVDF) is a ferroelectric polymer that exhibits β-phase, which can be further enhanced through the addition of fillers. This work reports on investigations of enhanced pyroelectric energy conversion in flexible composite films made from polyvinylidene fluoride and lead titanate (PVDF/PbTiO3) (PVDF/PTO). PVDF/PTO composite films are prepared by the incorporation of PTO to improve the β-phase of PVDF. A Fourier transform infrared (FTIR) spectroscopy analysis exhibits that the PVDF/PTO composite film with 5% PTO has a greater β-phase content than films with higher weight percentages (10% and 15% PTO). The pyroelectric current from the PVDF/PTO flexible composite film was measured using the phase-sensitive technique. The measurement revealed a notable figure of merit for pyroelectric energy conversion, reaching 0.282% with 5 wt% of PTO.

Diabetes management requires frequent blood glucose monitoring, yet invasive procedures impede testing. A noninvasive approach to detect random blood glucose (RBG) is crucial for early diagnosis and timely treatment. This work leverages Photoacoustic Spectroscopy for the detection of RBG due to its high sensitivity, specificity, and real-time monitoring capabilities. Therefore PAS has been implemented with a shallow dense neural network using a hybrid loss function (logcosh + huber loss) to estimate RBG. The augmentation of blood glucose is obtained by integrating biological parameters of a person like Body Mass Index, Age, and Spo2 with photoacoustic signal values. The intended hardware setup integrates with a Raspberry Pi 4 enabling real-time monitoring through the Thingspeak cloud platform. Testing with 105 in vivo samples demonstrated accuracies of 2.86 mg/dl (RMSE), 8.77 mg/dl (MAD), and 8.49% (MARD). Overall, an IoT-based PAS portable device is designed to provide smart healthcare services and quality care improvement.

The random blood glucose monitoring is a quick testing at any time to detect hyperglycemia and decrease the risk of common health complications. This paper focuses on a non-invasive in vivo random blood glucose estimation using the Photoacoustic Spectroscopy (PAS) technique. A portable system has been designed to obtain the pre-processed Photoacoustic (PA) signal from a finger using a Laser source of wavelength 905 nm. The Partial Least Square Regression algorithm is implemented where the PA signal feature values are utilized for calibrating coefficients, while the Body Mass Index parameter is included for better accuracy. The study has been conducted on 32 subjects, and the performance is observed with the Clarke Error Grid and Bland-Altman Plots. The Mean Absolute Relative Difference, Mean Absolute Difference, and Root Mean Square values are estimated as 8.9%, 13.75 mg/dl, and 16.13 mg/dl, respectively. Overall, the proposed non-invasive random blood glucose monitoring technique can facilitate the growth of point-of-care applications for frequent monitoring, particularly in resource-limited settings, which facilitates proper diabetic management.

Layered perovskites structures are an interesting candidate to explore as a potential electrolyte materials for Solid oxide fuel cell (SOFC) applications. However, achieving a high ionic conductivity (∼0.01 S cm⁻1 below 650 °C) remains a significant challenge to lowering the SOFC operating temperatures. SrBi2Ta2O9 (SBT), an Aurivillius-based layered perovskite, is a well-known ferroelectric material with TC of 320 °C. Site exchange and Bi volatility related defects lead to ionic conductivity in SBT above 700 °C. Here, we aim to control the defect chemistry by doping to promote the oxygen vacancies. We show that Mg doping at the Ta-site in the perovskite block results in 4-fold increase in the bulk conductivity of SBT 3.65 × 10−4 S cm−1 and improvement in the ionic transport number from 0.26 to 0.71. The study provides an opportunity to design new oxide ion conductors in layered ferroelectric oxides.

This extensive research delves into the intersection of MRI imaging and deep learning, in the task of identifying and categorizing brain tumors. In addition to models like VGG16 and ResNet101 a designed Convolutional Neural Network (CNN) was developed and thoroughly evaluated showcasing a range of techniques utilized. Augmentation methods were purposefully applied to enrich the dataset, enhancing the models' robustness and adaptability. Evaluation metrics, including the F1 score, recall, accuracy, and precision gave a general picture of the model's performance. Furthermore, leveraging Explainable AI (XAI) techniques such as LIME unveiled insights, into the decision-making processes underlying the models enhancing their interpretability and trustworthiness. The study findings ultimately underscore the potential of learning in revolutionizing automated brain tumor diagnosis and classification poised to enhance patient care pathways and medical diagnostic capabilities significantly.

Photoacoustic Spectroscopy (PAS) is a potential method for the noninvasive detection of blood glucose. However random blood glucose testing can help to diagnose diabetes at an early stage and is crucial for managing and preventing complications with diabetes. In order to improve the diagnosis, control, and treatment of Diabetes Mellitus, an appropriate approach of noninvasive random blood glucose is required for glucose monitoring. A polynomial kernel-based ridge regression is proposed in this paper to detect random blood glucose accurately using PAS. Additionally, we explored the impact of the biological parameter BMI on the regulation of blood glucose, as it serves as the primary source of energy for the body’s cells. The kernel function plays a pivotal role in kernel ridge regression as it enables the algorithm to capture intricate non-linear associations between input and output variables. Using a Pulsed Laser source with a wavelength of 905 nm, a noninvasive portable device has been developed to collect the Photoacoustic (PA) signal from a finger. A collection of 105 individual random blood glucose samples was obtained and their accuracy was assessed using three metrics: Root Mean Square Error (RMSE), Mean Absolute Difference (MAD), and Mean Absolute Relative Difference (MARD). The respective values for these metrics were found to be 10.94 (mg/dl), 10.15 (mg/dl), and 8.86%. The performance of the readings was evaluated through Clarke Error Grid Analysis and Bland Altman Plot, demonstrating that the obtained readings outperformed the previously reported state-of-the-art approaches. To conclude the proposed IoT-based PAS random blood glucose monitoring system using kernel-based ridge regression is reported for the first time with more accuracy.

A hybrid nanogenerator (HNG) offers both high output performance and flexibility by utilizing the synergy between piezoelectric and triboelectric mechanisms. Achieving high output performance, reproducibility, and mechanical stability in a HNG device is still a major challenge. Here, we demonstrate the design and fabrication of a flexible HNG device based on the composite of a lead-free piezoelectric ceramic and the triboelectric polymer poly(dimethylsiloxane) (PDMS). The piezoelectric ceramic oxide (Bi0.785K0.035Ba0.180)(Fe0.750Ti0250)O3 (BKBFT/MPB-piezo) exhibits improved piezoelectric properties at the morphotropic phase boundary (MPB) in the BiFeO3-Bi0.5K0.5TiO3-BaTiO3 ternary phase diagram. We find that the composite 90 wt % PDMS-10 wt % MPB-piezo offers optimum device performance and flexibility. Interestingly, the incorporation of multiwalled carbon nanotubes (MWCNTs), a conducting filler, significantly enhances the device’s performance without the aid of electric field poling. MWCNTs form nanoelectrical bridges that aid in charge transfer and improve the composite’s structural homogeneity. The 89 wt % PDMS-10 wt % MPB-piezo-1 wt % MWCNT composite displays a peak-to-peak open-circuit voltage (Vpp), short-circuit current (Isc), and power density (U) of 22 V, 1.8 μA, and 72 nW/cm2, respectively. Furthermore, we show the capability of the composite to be used as a wearable human pulse sensor.

The communication describes prospects of ferrite with composition Co0.88 Cu0.12 Fe2 O4 suitable for magnetic hyperthermia. Samples were processed by sol-gel method using polyethylene glycol (PEG) as chelating agent keeping ferrite to PEG weight ratios of 1:1, 1:2, and 1:3. Mean particle sizes of annealed powders at 400 ℃ ranging from 7.1 nm to 5.4 nm were in good agreement with the estimated crystallite sizes from X-ray diffraction patterns using Williamson-Hall analysis. Based on the variation of saturation magnetization with annealing temperature, the optimum weight ratio of ferrite to PEG was found to be 1:2. The heating efficiency of nanoparticles fabricated with ferrite-PEG weight ratio 1:2 was demonstrated using the magnetic induction heating experiment. The values of specific absorption rate 54 W/g and 83.3 W/g for the nanoparticle concentrations, 10 mg/mL and 15 mg/mL reveal the ability of Co-Cu ferrite nanoparticles as a heating agent.

Applied materials research and testing often involve measurements of material properties such as dielectric permittivity, impedance, piezoelectric coefficient, and pyroelectric current under non-ambient conditions and a controlled atmosphere. This requires simultaneous operation of multiple types of equipment and a controlled atmosphere for non-ambient conditions with computer-controlled data collection and operation. Here, we present the design and fabrication of a cost-effective measurement probe and measurement furnace with a capability of 1000°C under a controlled gas atmosphere. The setup, when used in tandem with an LCR meter or a source measure unit, can perform impedance and pyroelectric current measurements up to a temperature of 1000°C under a controlled atmosphere. We demonstrate the measurement capabilities in well-known ferroelectrics and oxide ion conductors including BaTiO3, (La0.9Sr0.1)(G0.9Mg0.1)O3-δ, Na0.5Bi0.5TiO3, and Pb(Zr, Ti)O3.

With emerging applications of the internet of things, technologies based on flexible materials draw much attention. In this aspect, flexible multiferroic materials might play a vital role in technologies such as energy harvesting, memory, sensor and much more. This work reports the pyroelectric studies on multiferroic polymer composite films coated on flexible substrates for pyroelectric energy conversion. Polyvinylidene fluoride/cobalt ferrite composite films were prepared by spin coating technique with different weight percentages of cobalt ferrite. The ferroelectric β-phase of polyvinylidene fluoride in composite films were confirmed by Fourier transform infrared spectroscopy. The polar β-phase of PVDF nucleated by the incorporation of CoFe2O4, through CF2 interaction with CoFe2O4 particles, in PVDF/CoFe2O4 composite films. The composite films reveal an increase in dielectric constant with the addition of cobalt ferrite. A maximum figure of merit value of 20.21% was observed in 15 wt % of CoFe2O4 composite film by using phase sensitive approach. The maximum magnetization was observed in 20 wt % of CoFe2O4 composite film. Improved film quality improves the pyroelectric coefficient and figure of merit for pyroelectric energy conversion.

Single-phase materials that are simultaneously ferroelectric and ferromagnetic at room temperature are promising for devices such as non-volatile random-access memory. Perovskite BiFeO3 which crystallizes in the polar rhombohedral structure (R3c) is ferroelectric and antiferromagnetic at room temperature. Here, we report a family of perovskite oxides in the BiFeO3 – Bi2/3TiO3 – ATiO3 (where A2+ is divalent alkaline earth metal ions e.g., Ca2+, Sr2+, Ba2+) ternary phase diagram that is polar as well as weak ferromagnetic above room temperature. The composition (Bi0.9167A0.075)(Fe0.9Ti0.1)O3 crystallizes in the polar rhombohedral structure space group R3c as corroborated by powder X-ray and neutron diffraction analysis. The nearly pure A-site perovskite possesses a long-range magnetic ordering above room temperature. These perovskites show a low dielectric loss, and the electrical response is dominated by grain contributions below 723 K.

Research on the development of green and renewable energy sources is becoming more important due to the increasing energy consumption. Various common physical effects can be used to produce generators for gathering energy from the surrounding environment. The uses of these devices for the growing Internet of Things can be significantly improved by adding flexibility. In this study, the improved pyroelectric figures of merit and pyroelectric coefficients of polymer-based flexible multiferroic composite films with two different ferrites are reported. With varying weight percentages of ferrite compositions, PVDF/manganese ferrite and PVDF/nickel ferrite composite films were prepared using the spin coating technique. The enhanced electroactive β-phase was observed, using hysteresis loops and Fourier transform infrared spectroscopy, in the composite films with 5 and 10 weight percentages of manganese ferrite and nickel ferrite, respectively. The dielectric permittivity and magnetization values of the films increased with the increasing weight percentage of ferrite. The pyroelectric current measurements revealed a maximum pyroelectric energy conversion figure of merit values of 8.67% and 12.19% on the PVDF/manganese ferrite and PVDF/nickel ferrite composite films with 5 wt% of MnFe2O4 content and 10 wt% NiFe2O4 content, respectively.

Ferroelectric films have been widely studied for their energy harvesting applications and flexible ferroelectric films for their piezoelectric energy harvesting. In this work, we explore tuning the PVDF/BaTiO3 composite flexible films for pyroelectric energy conversion applications. This work reports the influence of barium titanate particles (BaTiO3) in the formation of β-phase polyvinylidene fluoride (PVDF) on PVDF/BaTiO3 composite films based on Fourier transform infrared and Raman spectroscopic studies. PVDF/BaTiO3 composite films with different weight percentages of BaTiO3 were prepared by spin coating technique. Fourier transform infrared spectroscopy and Raman spectroscopic analysis of PVDF/BaTiO3 composite films indicated that the polar β-phase of PVDF nucleated by the incorporation of BaTiO3 through CF2 interaction with BaTiO3 particles as inferred from the filler percentage dependence study of vibration modes. The 15 wt% concentration of PVDF with 5 wt% of BaTiO3 composite film has higher β-phase content and better crystallinity. The improved film quality, in turn, enhances the pyroelectric coefficient and pyroelectric energy conversion figure of merit.

Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free perovskite that exhibits ferroelectricity below 300 °C. NBT and certain other ferroelectrics, e.g., Bi4Ti3O12, show oxide ionic conductivity on the order of 10-2 S cm-1 at elevated temperatures of 650 °C. The origin of ionic conductivity in these ferroelectric oxides has been explained in terms of bismuth deficiency and oxygen vacancy in the perovskite. There is a quest for materials as electrolytes with higher ionic conductivity and at temperatures below 650 °C. NBT-based ferroelectrics have been proposed to be one such candidate for low-temperature ionic conductors as electrolytes in solid oxide fuel cells (SOFCs). In this work, we have explored Na0.5Bi0.5TiO3-BaTiO3-BiFeO3 and studied the effect of composition on the conductivity behavior using impedance and modulus spectroscopy. We explain the nature of conductivity using the dependence of impedance on the partial pressure of oxygen. At a low BaTiO3 content, the composition Na0.45Bi0.49Ba0.05Fe0.05Mg0.019Ti0.931O3-δ (NBBTF-C) forms with a rhombohedral structure and shows an ionic conductivity of ∼1.02 × 10-3 S cm-1 at 600 °C, which is similar to that of NBT.

The present work reports on resistive switching (RS) characteristics of Neodymium (Nd)-doped bismuth ferrite (BFO) layers. The Nd (2–10 at%) doped BFO thin film layers were deposited using a spray pyrolysis method. The structural analysis reveals that a higher Nd doping concentration in BFO leads to significant distortion of the prepared Nd:BFO thin films from rhombohedral to tetragonal characteristics. The morphological analysis shows that all the deposited Nd:BFO thin films have regularly arranged grains. The X-ray photoelectron spectroscopy (XPS) analysis reveals that the prepared Nd:BFO thin films have a higher Fe 3+/Fe 2+ratio and less oxygen vacancy (VO) defects which enriches the ferroelectric characteristics in Nd:BFO layers. The polarization-electric field (P-E) and RS characteristics of the fabricated Nd:BFO-based RS device were examined. It was observed that the Nd (7 at%) doped BFO RS device shows large remnant polarization (P r) of 0.21 μC/cm2 and stable RS characteristics.

Ambient pressure stable perovskite oxides with all Bi3+ on the A-site are rare, with only four examples known. Due to the lone pair on Bi3+, these materials are seen as the best alternative to Pb-based piezoelectrics, which are used widely in society. The industry standard piezoelectric, Pb (Zr1 - xTix)O3, relies on the [001] polarization of PbTiO3, but there are currently no ambient pressure stable Bi-based perovskites with this polarization vector, preventing the creation of an analogous system. We present the full structural analysis of the orthorhombic phase of (1 - x)Bi (Ti3/8Fe2/8Mg3/8)O3 - xCaTiO3, which crystallizes in Pna21 symmetry with [001] polarization. This symmetry is rare and has only been reported twice for perovskites at ambient conditions. Analysis of maximum entropy method (MEM) models using synchrotron radiation powder X-ray diffraction reveals a disordered A-site configuration, and the MEM/Rietveld technique generates a structural model of this extreme disorder. Combined Rietveld analysis of X-ray and neutron diffraction data yields an accurate description of the local A-site configuration, which we use to understand our dielectric, ferroelectric, and piezoelectric measurements. These results give insight into how to stabilize this unique symmetry and inspire new design principles for Bi-based piezoelectrics.

The compound BiCr0.5Mn0.5O3, synthesized at high pressure and high temperature, shows a giant dielectric constant over a wide range of temperatures. Two relaxation processes are observed commencing around 200 K and 300 K. The low-temperature relaxation process is attributed to Maxwell–Wagner polarization at the grain boundary, whereas the second relaxation is attributed to the electrode polarization effect. Impedance spectroscopy reveals that the oxide is electrically inhomogeneous and dominant contribution arises from semiconducting grains and insulating grain boundary below room temperature. Above room temperature, the electrode polarization effect also contributes to the observed giant dielectric constant.

BiFeO3 is a ferroelectric and antiferromagnetic material at room temperature. In contrast to the weak ferromagnetism anticipated below TN = 640 K, it exhibits no macroscopic moment due to a cycloidal spin ordering. This study attempts to perturb the cycloidal spin ordering and improve the multiferroic properties by substitutions of Al and Sc at Fe site. The compounds BiFe1−xAlxO3 (0 ≤ x ≤ 0.3) and BiFe1−xScxO3 (0 ≤ x ≤ 0.2), synthesized at high pressures and temperatures, crystallize with perovskite structure in polar space group R3c. With increasing Al/Sc concentration, the compounds undergo marked changes in magnetic properties. While Al-substituted compounds were lossy and exhibited a Maxwell–Wagner effect, the Sc-substituted compounds exhibited ferroelectricity at room temperature.

1T Molybdenum disulfide (1T-MoS2) has been widely studied experimentally as an electrode for supercapacitors due to its excellent electrical and electrochemical properties. Whereas the capacitance value in MoS2 is limited due to the lower density of electrons near the Fermi level, and unable to fulfill the demand of industry i.e. quantum capacitance preferably higher than 300 μF/cm2. Here, we investigated the performance of 2H, 1T, and 1T′ phases of MoS2 in its pristine form and heterostructures with carbon-based structures as an electrode in the supercapacitors using density functional theory. Specifically, we reported that the underneath carbon nanotube (CNT) is responsible for the structural phase transition from 1T to 1T′ phase of MoS2 monolayer in 1T′-MoS2/CNT heterostructure. This is the main reason for a large density of states near Fermi level of 1T′-MoS2/CNT that exhibits high quantum capacitance (CQ) of 500 μF/cm2 at a potential of 0.6 V. Also, we observed that the nitrogen doping and defects in the underneath carbon surface amplify the CQ of heterostructure for a wider range of electrode potential. Therefore, the 1T′-MoS2/N doped CNT can be explored as an electrode for next-generation supercapacitors.

Although there is extensive literature covering the biomedical applications of superparamagnetic iron oxide nanoparticles (SPIONs), the phase of the iron oxide core used is not often taken into account when cell labelling and tracking studies for regenerative medicine are considered. Here, we use a co-precipitation reaction to synthesise particles of both magnetite- (Fe3O4) and maghemite- (γ-Fe2O3) based cores and consider whether the extra synthesis step to make maghemite based particles is advantageous for cell tracking.

The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO3-type cation ordering that breaks inversion symmetry may be combined with long-range magnetic ordering of high spin d5 cations above room temperature in the AFeO3 system. We report the synthesis of a polar corundum GaFeO3 by a high-pressure, high-temperature route and demonstrate that its polarity arises from partial LiNbO3-type cation ordering by complementary use of neutron, X-ray, and electron diffraction methods. In situ neutron diffraction shows that the polar corundum forms directly from AlFeO3-type GaFeO3 under the synthesis conditions. The A3+/Fe3+ cations are shown to be more ordered in polar corundum GaFeO3 than in isostructural ScFeO3. This is explained by DFT calculations which indicate that the extent of ordering is dependent on the configurational entropy available to each system at the very different synthesis temperatures required to form their corundum structures. Polar corundum GaFeO3 exhibits weak ferromagnetism at room temperature that arises from its Fe2O3-like magnetic ordering, which persists to a temperature of 408 K. We demonstrate that the polarity and magnetization are coupled in this system with a measured linear magnetoelectric coupling coefficient of 0.057 ps/m. Such coupling is a prerequisite for potential applications of polar corundum materials in multiferroic/magnetoelectric devices. (Graph Presented).

The discovery of new materials is hampered by the lack of efficient approaches to the exploration of both the large number of possible elemental compositions for such materials, and of the candidate structures at each composition. For example, the discovery of inorganic extended solid structures has relied on knowledge of crystal chemistry coupled with time-consuming materials synthesis with systematically varied elemental ratios. Computational methods have been developed to guide synthesis by predicting structures at specific compositions and predicting compositions for known crystal structures, with notable successes. However, the challenge of finding qualitatively new, experimentally realizable compounds, with crystal structures where the unit cell and the atom positions within it differ from known structures, remains for compositionally complex systems. Many valuable properties arise from substitution into known crystal structures, but materials discovery using this approach alone risks both missing best-in-class performance and attempting design with incomplete knowledge. Here we report the experimental discovery of two structure types by computational identification of the region of a complex inorganic phase field that contains them. This is achieved by computing probe structures that capture the chemical and structural diversity of the system and whose energies can be ranked against combinations of currently known materials. Subsequent experimental exploration of the lowest-energy regions of the computed phase diagram affords two materials with previously unreported crystal structures featuring unusual structural motifs. This approach will accelerate the systematic discovery of new materials in complex compositional spaces by efficiently guiding synthesis and enhancing the predictive power of the computational tools through expansion of the knowledge base underpinning them.

Superparamagnetic iron oxide nanoparticles (SPIONs) are widely used as contrast agents for stem cell tracking using magnetic resonance imaging (MRI). The total mass of iron oxide that can be internalised into cells without altering their viability or phenotype is an important criterion for the generation of contrast, with SPIONs designed for efficient labelling of stem cells allowing for an increased sensitivity of detection. Although changes in the ratio of polymer and iron salts in co-precipitation reactions are known to affect the physicochemical properties of SPIONs, particularly core size, the effects of these synthesis conditions on stem cell labelling and magnetic resonance (MR) contrast have not been established. Here, we synthesised a series of cationic SPIONs with very similar hydrodynamic diameters and surface charges, but different polymer content. We have investigated how the amount of polymer in the co-precipitation reaction affects core size and modulates not only the magnetic properties of the SPIONs but also their uptake into stem cells. SPIONs with the largest core size and lowest polymer content presented the highest magnetisation and relaxivity. These particles also had the greatest uptake efficiency without any deleterious effect on either the viability or function of the stem cells. However, for all particles internalised in cells, the T2 and T2 * relaxivity was independent of the SPION's core size. Our results indicate that the relative mass of iron taken up by cells is the major determinant of MR contrast generation and suggest that the extent of SPION uptake can be regulated by the amount of polymer used in co-precipitation reactions. Copyright © 2016 John Wiley & Sons, Ltd.

Ferroelectric and ferromagnetic materials exhibit long-range order of atomic-scale electric or magnetic dipoles that can be switched by applying an appropriate electric or magnetic field, respectively. Both switching phenomena form the basis of non-volatile random access memory, but in the ferroelectric case, this involves destructive electrical reading and in the magnetic case, a high writing energy is required. In principle, low-power and high-density information storage that combines fast electrical writing and magnetic reading can be realized with magnetoelectric multiferroic materials. These materials not only simultaneously display ferroelectricity and ferromagnetism, but also enable magnetic moments to be induced by an external electric field, or electric polarization by a magnetic field. However, synthesizing bulk materials with both long-range orders at room temperature in a single crystalline structure is challenging because conventional ferroelectricity requires closed-shell d0 or s2 cations, whereas ferromagnetic order requires open-shell dn configurations with unpaired electrons. These opposing requirements pose considerable difficulties for atomic-scale design strategies such as magnetic ion substitution into ferroelectrics. One material that exhibits both ferroelectric and magnetic order is BiFeO3, but its cycloidal magnetic structure precludes bulk magnetization and linear magnetoelectric coupling. A solid solution of a ferroelectric and a spin-glass perovskite combines switchable polarization with glassy magnetization, although it lacks long-range magnetic order. Crystal engineering of a layered perovskite has recently resulted in room-temperature polar ferromagnets, but the electrical polarization has not been switchable. Here we combine ferroelectricity and ferromagnetism at room temperature in a bulk perovskite oxide, by constructing a percolating network of magnetic ions with strong superexchange interactions within a structural scaffold exhibiting polar lattice symmetries at a morphotropic phase boundary (the compositional boundary between two polar phases with different polarization directions, exemplified by the PbZrO3 -PbTiO3 system) that both enhances polarization switching and permits canting of the ordered magnetic moments. We expect this strategy to allow the generation of a range of tunable multiferroic materials.

Lead-free bismuth-based perovskite oxides with polarization directed along the [001]p primitive perovskite unit cell edge, analogous to tetragonal PbTiO3, are synthesized at ambient pressure. Enhanced piezoelectric properties, large polarizations, and high depolarization temperatures are observed in the wide morphotropic phase boundary region formed with a rhombohedral phase, with up to 92.5% Bi on the perovskite A site.

Tracking stem cells in vivo using non-invasive techniques is critical to evaluate the efficacy and safety of stem cell therapies. Superparamagnetic iron oxide nanoparticles (SPIONs) enable cells to be tracked using magnetic resonance imaging (MRI), but to obtain detectable signal cells need to be labelled with a sufficient amount of iron oxide. For the majority of SPIONs, this can only be obtained with the use of transfection agents, which can adversely affect cell health. Here, we have synthesised a library of dextran-based polymer coated SPIONs with varying surface charge from -1.5 mV to +18.2 mV via a co-precipitation approach and investigated their ability to be directly internalised by stem cells without the need for transfection agents. The SPIONs were colloidally stable in physiological solutions. The crystalline phase of the particles was confirmed with powder X-ray diffraction and their magnetic properties were characterised using SQUID magnetometry and magnetic resonance. Increased surface charge led to six-fold increase in uptake of particles into stem cells and higher MRI contrast, with negligible change in cell viability. Cell tracking velocimetry was shown to be a more accurate method for predicting MRI contrast of stem cells compared to measuring iron oxide uptake through conventional bulk iron quantification.

Crystalline materials that combine electrical polarization and magnetization could be advantageous in applications such as information storage, but these properties are usually considered to have incompatible chemical bonding and electronic requirements. Recent theoretical work on perovskite materials suggested a route for combining both properties. We used crystal chemistry to engineer specific atomic displacements in a layered perovskite, (CaySr1-y)1.15Tb1.85Fe2O7, that change its symmetry and simultaneously generate electrical polarization and magnetization above room temperature. The two resulting properties are magnetoelectrically coupled as they arise from the same displacements.

This contribution focuses on the use of modified Rayleigh law as a technique for determining the intrinsic and extrinsic (reversible/irreversible) contributions to the piezoelectric effect up to 150 °C across a broad compositional space, augmenting previous understanding of the BiFeO3-(K0.5Bi0.5)TiO3-PbTiO3 system. At room temperature, a mechanistic explanation of the correlation between crystal symmetry, i.e., tetragonal spontaneous strain, xs, and the Rayleigh relations using Landau theory is provided. The intrinsic response was found to be heavily dependent upon the tetragonal xs, whereby an optimisation between polarization and permittivity was elucidated, leading to enhanced piezoelectric charge coefficients. A c/a ratio of ∼1.041 was identified at which the room temperature intrinsic and extrinsic effects were at a maximum; a dinit of 183 × 10-12m/V and Rayleigh coefficient of 59 × 10-18m2/V2 were measured, resulting in the largest piezoelectric charge coefficients. The piezoelectric charge coefficient d33, intrinsic and extrinsic contributions of these materials were all found to increase up to 150 °C while adhering to the Rayleigh model. The reversible extrinsic component of the total reversible response, dinit, was calculated to be relatively minor, 4.9% at room temperature, increasing to 12.1% at 150 °C, signifying its increasing influence to the piezoelectric effect, as domain wall motion is thermally activated. Hence, the phenomenological interpretation provided here may be used as a roadmap to elucidate the origins of the temperature dependence of the piezoelectric effect.

The piezoelectric effect in poly(vinylidene fluoride), PVDF, was discovered over four decades ago and since then, significant work has been carried out aiming at the production of high β-phase fibres and their integration into fabric structures for energy harvesting. However, little work has been done in the area of production of "true piezoelectric fabric structures" based on flexible polymeric materials such as PVDF. In this work, we demonstrate "3D spacer" technology based all-fibre piezoelectric fabrics as power generators and energy harvesters. The knitted single-structure piezoelectric generator consists of high β-phase (∼80%) piezoelectric PVDF monofilaments as the spacer yarn interconnected between silver (Ag) coated polyamide multifilament yarn layers acting as the top and bottom electrodes. The novel and unique textile structure provides an output power density in the range of 1.10-5.10 μW cm-2 at applied impact pressures in the range of 0.02-0.10 MPa, thus providing significantly higher power outputs and efficiencies over the existing 2D woven and nonwoven piezoelectric structures. The high energy efficiency, mechanical durability and comfort of the soft, flexible and all-fibre based power generator are highly attractive for a variety of potential applications such as wearable electronic systems and energy harvesters charged from the ambient environment or by human movement. This journal is © 2014 the Partner Organisations.

Members of the YFe 1-xMn xO 3 (0≤x≤0.45) family crystallize in the GdFeO 3 type orthorhombic perovskite structure (space group Pnma) where the Fe and Mn ions are disordered at the 4b crystallographic site. Upon substitution of Mn at the Fe-site in the canted antiferromagnetic YFeO 3 (T N=640 K), a first-order spin-reorientation transition occurs at a temperature, T SR, where the magnetic structure changes from the canted to a collinear state. With increasing Mn-concentration, T SR increases whereas T N decreases. Neutron diffraction studies on the x=0.4 sample reveal that the spin structure changes from Γ 4 to Γ 1 below T SR. Intriguingly, when x=0.4 and 0.45, a temperature-induced magnetization reversal is observed below a compensation temperature T (T<T SR<T N). The reversal is explained on the basis of a ferrimagnetic ground state resulting from antiferromagnetic coupling of the canted moments of Fe-O-Fe and Mn-O-Mn with that of Fe-O-Mn ordering. © 2012 Elsevier Inc. All rights reserved.

Rare-earth orthochromites, RCrO 3 (R = rare-earth and Y) with magnetic R-ions are reported to exhibit ferroelectricity at the magnetic ordering temperature of Cr 3+-ions (Rajeswaran, B.; Khomskii, D. I.; Zvezdin, A. K.; Sundaresan, A.; Rao, C. N. R. arXiv2012, 1201, 0826v1). Interestingly, we observe ferroelectricity at the Néel temperature of orthochromites containing a nonmagnetic R-ion (Y) upon introducing cation-disorder at the Cr-site by incorporation of another magnetic ion of nonequivalent spin. For example, the weakly ferromagnetic perovskite, YCr 0.5Fe 0.5O 3, where the Cr 3+ (S = 3/2) and Fe 3+ (S = 5/2) ions at the B-site are disordered, exhibits ferroelectricity at T N = 260 K. Ferroelectricity is observed not only when the relative proportions of Fe 3+ and Cr 3+ ions as in YCr 1-xFe xO 3 are varied but also when Y 3+ ions are replaced by other nonmagnetic R-ion and the transition metal ions changed as in YCr 1-xMn xO 3. While the local polarization cancels out in the weakly ferromagnetic YMO 3 (M = Cr and Fe), a nonzero polarization in these materials seem to arise due to disordered transition metal ions of nonequivalent spins. © 2012 American Chemical Society.

(Bi 0.5Sr 0.5)(Fe 0.5Mn 0.5)O 3 crystallizes in a rhombohedral structure, with space group R3c, where the cations Bi 3+/Sr 2+ and Fe 3+/Mn 4+ occupy 6a and 6b sites respectively. Neutron diffraction, Mössbauer and magnetization measurements confirm long range antiferromagnetic ordering of the Fe 3+ and Mn 4+ moments at T N (226 K). Below T N, this oxide exhibits a cluster glass behavior and at low temperatures (∼30 K) a spin glass state is observed. The complex magnetic behavior is attributed to cation disorder in the system. Magnetic properties of this oxide are compared with those of the isostructural Bi 0.5La 0.5Fe 0.5Mn 0.5O 3 where both Fe and Mn ions exist in trivalent state. © 2012 The Royal Society of Chemistry.

We report magnetic, dielectric, and magnetodielectric responses of the pure monoclinic bulk phase of partially disordered La 2NiMnO 6, exhibiting a spectrum of unusual properties and establish that this compound is an intrinsically multiglass system with a large magnetodielectric coupling (8%-20%) over a wide range of temperatures (150-300K). Specifically, our results establish a unique way to obtain colossal magnetodielectricity, independent of any striction effects, by engineering the asymmetric hopping contribution to the dielectric constant via the tuning of the relative-spin orientations between neighboring magnetic ions in a transition-metal oxide system. We discuss the role of antisite (Ni-Mn) disorder in emergence of these unusual properties. © 2012 American Physical Society.

We present combined experimental and theoretical studies on the magnetic properties of a solid solution between yttrium orthoferrite and yttrium orthochromite systems, YFe 1-xCr xO 3 (0≤x≤ 1), where Fe 3+ and Cr 3+ ions are distributed randomly at the same crystallographic site (4b). We found that all the compositions exhibit weak ferromagnetism below the Néel temperature that decreases nonlinearly with increasing x, while certain intermediate compositions (x=0.4,0.5) show a compensation point and magnetization reversal. This unusual behavior is explained based on a simple model comprising the isotropic superexchange and the antisymmetric Dzyaloshinskii-Moriya interactions. This model explains the magnetization behavior in the entire range of doping and temperature including the magnetization reversal which results from an interplay of various DM interactions such as, Fe-O-Fe, Cr-O-Cr and Fe-O-Cr. © Copyright EPLA, 2012.

AlFeO3, GaFeO3 and Al0.5Ga0.5FeO3, all crystallizing in a non-centrosymmetric space group, are multiferroic and also exhibit magnetodielectric properties, with Al0.5Ga0.5FeO3 showing an unusually large magnetocapacitance at 300 K. © The Royal Society of Chemistry.

Combining experiments with first-principles calculations, we show that site-specific doping of Mn into SrTiO3 has a decisive influence on the dielectric properties of these doped systems. We find that phonon contributions to the dielectric constant invariably decrease sharply on doping at any site. However, a sizable, random dipolar contribution only for Mn at the Sr site arises from a strong off-centric displacement of Mn in spite of Mn being in a non-d0 state; this leads to a large dielectric constant at higher temperatures and gives rise to a relaxor ferroelectric behavior at lower temperatures. We also investigate magnetic properties in detail and critically reevaluate the possibility of a true multiglass state in such systems. © 2011 American Physical Society.

We report the observation of magnetoelectric and magnetodielectric effects at different temperatures in Mn-substituted yttrium orthoferrite, YFe 1-xMnxO3(0.1≤x≤0.40). Substitution of Mn in antiferromagnetic YFeO3(TN=640K) induces a first-order spin-reorientation transition at a temperature, TSR, which increases with x whereas the Néel temperature (TN) decreases. While the magnetodielectric effect occurs at TSR and TN, the ferroelectricity appears rather at low temperatures. The origin of magnetodielectric effect is attributed to spin-phonon coupling as evidenced from the temperature dependence of Raman phonon modes. The large magnetocapacitance (18% at 50 kOe) near TSR=320K and high ferroelectric transition temperature (∼115K) observed for x=0.4 suggest routes to enhance magnetoelectric effect near room temperature for practical applications. © 2011 American Physical Society.

The first-order spin-reorientation transition in the Mn-substituted yttrium orthoferrites, YFe1xMnxO3 (x=0.1, 0.15 and 0.2), has been investigated using 57Fe Mössbauer spectroscopy. Owing to its large anisotropy, substitution of Mn3+ ions in YFeO 3 induces a spin-reorientation transition from the low-temperature antiferromagnetic state to a high-temperature weak ferromagnetic state. With increasing x, the spin-reorientation transition temperature (TSR) increases whereas the Néel temperature (TN) decreases. Analysis of the Mössbauer spectra unambiguously confirms the occurrence of spin reorientation relative to crystal axes. At a given temperature, the mean hyperfine field decreases with the increasing Mn concentration. The variation of canting angle with temperature for YFe0.85Mn0.15O 3 has been estimated. © 2011 IOP Publishing Ltd.

BiFe0.5Mn0.5O3 could be stabilized in the perovskite structure by preparing it under high pressure and temperature. It has an orthorhombic structure with a possible ordered arrangement of Fe and Mn double rows and shows a magnetic ordering at high temperature (270 K). Low-temperature isothermal-magnetization measurements indicate the ground state to be antiferromagnetic with a spin canting. Surprisingly, it exhibits magnetization reversal at low applied fields below a compensation temperature, T*. Below T*, the sign of the magnetization can be switched between negative and positive value reversibly by increasing and decreasing the field. Magnetization reversal in this oxide seems to result from a competition between single-ion magnetocrystalline anisotropy and antisymmetric Dzyaloshinsky-Moriya interactions. © 2010 The American Physical Society.

BiCr0.5Mn0.5O3, synthesized at high pressure and high temperature, has a monoclinic structure (space group C2/c) at room temperature with a = 9.4590(3) Å, b = 5.5531(2) Å, c = 9.6465(3) Å and β = 108.149(2)°. It undergoes a structural transition from the monoclinic to an orthorhombic (Pnma) symmetry around 650 K. Magnetic measurements show three distinct anomalies at 25, 50 and 97 K. AC susceptibility measurements confirm the occurrence of the magnetic anomalies, but suggest no spin frustration. Interestingly, this oxide shows a giant dielectric constant at room temperature. Two clear relaxation processes commencing around 200 K and 300 K are exhibited by this material. The first relaxation process is due to Maxwell-Wagner polarization at the grain boundary whereas the second relaxation may arise from hopping of electrons in the B-site. © 2010 The Royal Society of Chemistry.

The orthorhombic perovskite, (La1-x/2Bix/2)(Fe 0.5Cr0.5)O3 was investigated for 0≤x≤1. Itsspace group, Pnma, compatible with the disordering of iron and chromium in the B sites, confirms previous observations. More importantly this compound is found to be an uncompensated weak ferromagnet, with a very peculiar zero magnetization behaviour, generally observed for ordered magnetic cations in the B sites. It exhibits a magnetic transition at high temperature (TC) above 450K, while the zero magnetization occurs between 100 and 160K depending on the x-value. The AC magnetic susceptibility study shows that this compound does not exhibit a spin glass or cluster glass behaviour, in contrast to what was suggested for the x = 0 compound. This zero magnetization phenomenon can be interpreted by the fact that this perovskite is an uncompensated weak ferromagnet, which consists of canted weak ferromagnetic domains and clusters of pure chromium and pure iron composition, antiferromagnetically coupled through Cr-O-Fe interactions. © 2009 IOP Publishing Ltd.

Epitaxial bilayered thin films consisting of La0.6Sr 0.4MnO3 (LSMO) and 0.7Pb (Mg1/3Nb 2/3) O3 -0.3 PbTiO3 (PMN-PT) layers of relatively different thicknesses were fabricated on LaNiO3 coated LaAlO3 (100) single crystal substrates by pulsed laser ablation technique. The crystallinity, ferroelectric, ferromagnetic, and magnetodielectric properties have been studied for all the bilayered heterostructures. Their microstructural analysis suggested possible Stranski-Krastanov type of growth mechanism in the present case. Ferroelectric and ferromagnetic characteristics of these bilayered heterostructures over a wide range of temperatures confirmed their biferroic nature. The magnetization and ferroelectric polarization of the bilayered heterostructures were enhanced with increasing PMN-PT layer thickness owing to the effect of lattice strain. In addition, evolution of the ferroelectric and ferromagnetic properties of these heterostructures with changing thicknesses of the PMN-PT and LSMO layers indicated possible influence of several interfacial effects such as space charge, depolarization field, domain wall pinning, and spin disorder on the observed properties. Dielectric properties of these heterostructures studied over a wide range of temperatures under different magnetic field strengths suggested a possible role of elastic strain mediated magnetoelectric coupling behind the observed magnetodielectric effect in addition to the influence of rearrangement of the interfacial charge carriers under an applied magnetic field. © 2009 American Institute of Physics.

High temperature dielectric measurement on rhombohedral Ba2BiTaO6 shows an anomaly at 250 °C where there is a structural transition from the room temperature rhombohedral (R-3) to high temperature cubic (Fm-3m) phase as inferred from the high temperature X-ray diffraction data. Impedance spectroscopic study reveals that the contribution to the electrical response comes from grain as well as from grain boundary. Grain boundary capacitance does not show significant temperature dependence whereas grain capacitance increases with increasing temperature. Both of these conduction processes are similar in nature as indicated from the close value of activation energies as derived from the Arrhenius plot. © 2008 Elsevier Masson SAS. All rights reserved.

Epitaxial heterostructures of La0.6Sr0.4MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 were fabricated on LaNiO3 coated LaAlO3 (100) substrates by pulsed laser ablation. Ferromagnetic and ferroelectric hysteresis established their biferroic nature. Dielectric behaviour studied under different magnetic fields over a wide range of temperatures revealed that the capacitance in these heterostructures varies with the applied magnetic field. Appearance of magnetocapacitance and its dependence on temperature and magnetic field strength strongly indicated the possibility of strain mediated magnetoelectric coupling in these heterostructures. © 2008 Elsevier Ltd. All rights reserved.

A bottom-up approach has been used to tune the morphology of single-crystalline hematite from hollow spheres to nanocups. The mechanism involves the formation of nanocups through buckling of the spheres, similar to a deflated ball (see picture). As the shape changes, there is a drastic change in magnetic properties. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

The crystal structure of ordered perovskite BaBi0.5 3+(Bi0.25+Nb0.35+)O 3 was analyzed using electron and neutron diffraction to observe ferroelectricity with high Curie temperature. Analysis of room-temperature neutron diffraction data of BBN showed that the room-temperature structure is rhombohedral with centrosymmetric space group R3̄. Temperature dependence of powder X-ray diffraction showed that there is a structural transition between 450 and 700°C. Temperature dependent on dielectric constant and powder X-ray diffraction measurements show that ferroelectricity is consistent with a phase transition at around 420°C. Results show that room temperature rombohedral structure transforms to cubic structure at high temperature.