Temperature Dependent Dielectric Measurements Research Articles

Universal Dielectric Response in Electronically Correlated Functional Oxides CaCu3Ti4O12, LaFeO3, YFe0.5Cr0.5O3 and their Nanocomposites: A Comparative Study

AbstractCaCu3Ti4O12 (CCTO), LaFeO3 (LFO) and YFe0.5Cr0.5O3 (YFCO) were synthesized via conventional sol–gel auto–combustion method using citric acid as gelling agent. The X‐ray diffraction analysis revealed the phase purity of the samples. The energy dispersive X‐ray (EDX) analysis confirms the stoichiometry of the pristine phases. The average particle size obtained from the field emission Scanning electron microscopy (FE−SEM) images revealed that CaCu3Ti4O12 exhibits a broad range of particle size starting from a couple of hundreds of nanometer to micrometer, whereas that for LaFeO3 and YFe0.5Cr0.5O3 are about 110 nm and 50 nm, respectively. We have fabricated the new composites: CCTO–LFO, CCTO–YFCO and LFO–YFCO. The grain sizes of the composite phases are consistent with the pristine phases as they are prepared by at lower sintering temperatures and duration. The dielectric properties of these ceramic composites were compared to those of the pristine phases. The temperature and frequency dependent dielectric measurements reveal a wide range of dielectric constant with moderate tan δ values. The temperature dependent dielectric constant of the investigated samples varies from 100 to 1500 at room temperature and the data have been analyzed using universal dielectric response (UDR) model.

Temperature-dependent dielectric relaxation measurements of (acetamide + K/Na SCN) deep eutectic solvents: Decoding the impact of cation identity via computer simulations.

The impact of successive replacement of K+ by Na+ on the megahertz-gigahertz polarization response of 0.25[fKSCN + (1 - f)NaSCN] + 0.75CH3CONH2 deep eutectic solvents (DESs) was explored via temperature-dependent (303 ≤ T/K ≤ 343) dielectric relaxation (DR) measurements and computer simulations. Both the DR measurements (0.2 ≤ ν/GHz ≤ 50) and the simulations revealed multi-Debye relaxations accompanied by a decrease in the solution static dielectric constant (ɛs) upon the replacement of K+ by Na+. Accurate measurements of the DR response of DESs below 100MHz were limited by the well-known one-over-frequency divergence for conducting solutions. This problem was tackled in simulations by removing the zero frequency contributions arising from the ion current to the total simulated DR response. The temperature-dependent measurements revealed a much stronger viscosity decoupling of DR times for Na+-containing DES than for the corresponding K+ system. The differential scanning calorimetry measurements indicated a higher glass transition temperature for Na+-DES (∼220K) than K+-DES (∼200K), implying more fragility and cooperativity for the former (Na+-DES) than the latter. The computer simulations revealed a gradual decrease in the average number of H bonds (⟨nHB⟩) per acetamide molecule and increased frustrations in the average orientational order upon the replacement of K+ by Na+. Both the measured and simulated ɛs values were found to decrease linearly with ⟨nHB⟩. Decompositions of the simulated DR spectra revealed that the cation-dependent cross interaction (dipole-ion) term contributes negligibly to ɛs and appears in the terahertz regime. Finally, the simulated collective single-particle reorientational relaxations and the structural H-bond fluctuation dynamics revealed the microscopic origin of the cation identity dependence shown by the measured DR relaxation times.

Achieving giant field-induced strain in BS-modified BNKT lead-free ferroelectric ceramics

Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 (BNT-BKT) binary systems with the morphotropic phase boundary (MPB) are promising candidates for piezoelectric actuators. However, pure BNT-BKT ceramics commonly exhibit unfavorable electric field-induced strain, which is insufficient to meet the requirements for actuator applications. Rare earth-containing dopants have been extensively explored to modify various materials due to their unique optical, magnetic, and electronic properties. Here, by introducing rare earth ion-containing dopants BiScO3 (BS), the electrical properties of Bi0.5(Na0.84K0.16)0.5TiO3 (BNKT) lead-free ferroelectric ceramics have been modified. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results suggest that the introduction of BS results in an increase in tetragonal (T) phases, reduced grain sizes, and uniform morphologies. Ferroelectric measurements demonstrate that the BS-containing ceramics show slimmer hysteresis loops. The BNKT-2BS ceramics show a noteworthy improvement in electric field-induced strain, with bipolar and monopolar strains of 0.58% and 0.68%, respectively, which are almost 4 times and 6 times higher than those of pure BNKT ceramics. Furthermore, the corresponding normalized strain (d33*) also achieves high values of 967 pm/V and 1133 pm/V, respectively. Temperature-dependent dielectric measurements reveal that BS-containing ceramics exhibit good relaxor characteristics with frequency dispersion and diffuse phase transitions. This study presents a sufficient and feasible strategy for the optimization of strain performance in large displacement actuator applications.

Mild chemistry synthesis of ultrathin Bi2O2S nanosheets exhibiting 2D-ferroelectricity at room temperature.

Modern technology demands miniaturization of electronic components to build small, light, and portable devices. Hence, discovery and synthesis of new non-toxic, low cost, ultra-thin ferroelectric materials having potential applications in various electronic and optoelectronic devices are of paramount importance. However, achieving room-temperature ferroelectricity in two dimensional (2D) ultra-thin systems remains a major challenge as conventional three-dimensional ferroelectric materials lose their ferroelectricity when the thickness is brought down below a critical value owing to the depolarization field. Herein, we report room-temperature ferroelectricity in ultra-thin single-crystalline 2D nanosheets of Bi2O2S synthesized by a simple, rapid, and scalable solution-based soft chemistry method. The ferroelectric ground state of Bi2O2S nanosheets is confirmed by temperature-dependent dielectric measurements as well as piezoelectric force microscopy and spectroscopy. High resolution transmission electron microscopy analysis and density functional theory-based calculations suggest that the ferroelectricity in Bi2O2S nanosheets arises due to the local distortion of Bi2O2 layers, which destroys the local inversion symmetry of Bi2O2S.

Tailoring the structural, optical, electrical and multiferroic properties of Sm1-xRxFeO3 (x = 0.0 and 0.5; R = Pr, Nd, and Gd) and their synergistic photocatalytic activity

In this work, nanocrystalline Sm1-xRxFeO3 (x = 0.0 and 0.5; RPr, Nd, and Gd) samples have been synthesized via auto-combustion method and characterized to understand their microstructural, optical, electrical and multiferroic properties. X-ray diffraction data in combination with the FTIR spectra revealed the monophase and distorted orthorhombic configuration of all the samples with Pbnm space group. Rietveld refinement displayed a reduction in the bond length as well as the bond angle in the Sm0.5Gd0.5FeO3 sample. Raman spectra exhibit compressive strain in Sm0.5Gd0.5FeO3 nanoparticles; this finding is further supported by the XRD analysis. UV–visible spectroscopy manifests a reduction in the optical energy bandgap on moving Gd to Pr in Sm0.5R0.5FeO3 system. Transmission electron microscopy (TEM) images in combination with energy dispersive x-ray (EDX) spectra reveal the non-uniform surface morphology with the agglomerated nature of nanoparticles and affirm the elemental compositions of all the samples. The room temperature P-E and M − H loops infer the multiferroic nature of all samples. Electron paramagnetic resonance (EPR) analysis divulges the weakening of the super-exchange interactions in Sm0.5R0.5FeO3 system. DC electrical resistivity measurements reflect semiconductor-like behaviour in all prepared samples. The dielectric behaviour of the samples is in accordance with the “universal dielectric response” model. The temperature-dependent dielectric measurements of all prepared samples have been performed at 1 kHz to determine the Néel temperature (TN). The photocatalytic investigation depicts the superior photocatalytic response of Sm0.5Pr0.5FeO3 nanoparticles under solar-light irradiation through the synergism of semiconductor-photocatalyzed oxidation and heterogeneous Fenton-like reaction.

Structural and dielectric properties of Y3+ doped SrTiO3: a novel anode materials for solid oxide fuel cell

An ongoing and elusive task is to create single phase anode materials for solid oxide fuel cells (SOFC). Compared to the typical Ni-YSZ cermet anode, perovskite oxide based anode material has a number of benefits. Here, we present the structural and electrical characteristics of Y3+ doped SrTiO3 ceramics that are used as the anode in solid oxide fuel cells. The samples with nominal composition x = 0 and 0.05 were synthesized by high energy ball milling. The powder X-ray diffraction pattern reveals that the synthesized samples crystallize into cubic crystal structure with space group Pm3m for both the compositions. The samples were sintered at a temperature of 1300 °C for 6h. The sintered density of the samples was found to be greater than 97%. The temperature dependent dielectric measurement studies reveal that dielectric constant increases with yttrium doping and shows relaxer behavior. A higher dielectric constant and electrical conductivity was observed for the Y-doped sample which fulfill the basic requirement for anode materials of solid oxide fuel cells.

High-entropy (Na0.2Bi0.2Ba0.2Sr0.2Zn0.2)TiO3 ceramics with enhanced energy storage density and reliable stability

High-entropy ceramics (HECs) have gained increasingly recent interest due to their fantastic physiochemical properties and rich compositions. The investigation of energy storage performance based on the temperature and frequency stability of HECs is still at an early stage, with limited reported studies. Here, we report lead-free (Na0.2Bi0.2Ba0.2Sr0.2Zn0.2)TiO3 (NBBSZT) HECs by a solid-state approach with a pressureless sintering process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies demonstrate that NBBSZT HECs show a pure perovskite structure, uniform morphology and element distribution. Ferroelectric measurements indicate that the NBBSZT HECs exhibit an improved energy storage density of 1.03 J/cm3 and an efficiency of 77%, which is approximately 5 times and 17 times enhancement compared to Bi0.5Na0.5TiO3 (BNT) ceramics, respectively. The NBBSZT HECs also demonstrate excellent thermal stability and satisfactory frequency stability. More interestingly, the dielectric property studies show that the NBBSZT HECs exhibit frequency dispersion and diffuse phase transition. Temperature-dependent dielectric measurements indicate that the NBBSZT HECs exhibit better relaxor characteristics than that of BNT ceramics. These studies reveal that the high-entropy strategy provides a potential platform for designing ferroelectric ceramics.

Quenching-driven advancements in functional properties of high-temperature lead-free Sc, Ga modified 0.67BiFeO3-0.33BaTiO3 relaxor ceramics

The processing method is one of the most important deciding factors in the fabrication of BiFeO3–BaTiO3 (BF-BT) based piezoceramics because of the Bi2O3 volatization. It significantly influences the functional properties, including the piezoelectric coefficients, dielectric properties, and microstructure. This study presents a significant advancement in the realm of high-temperature lead-free piezoelectric ceramics in terms of understanding effects of processing method on functional properties. In this light, a novel ceramic solid-solution, 0.67{Bi(Fe0.97Ga0.03)1-xScxO3}-0.33(BaTiO3) with x ≤ 0.07, incorporating Scandium (Sc) and Gallium (Ga) modifications, was meticulously designed and synthesized. Impact of two distinct sintering methods, namely air quenching (AQ) and closed sintering (CS) on the structure and properties of the developed materials are investigated. X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analysis verified the formation of pure perovskite phases with successful incorporation of Sc and Ga into the 0.67BF-0.33BT lattice. The FTIR analysis revealed a sharp absorptive band in the 590-604 cm−1 range, corresponding to the signature of stretching and bending vibrations of (Ti/Fe)O6 octahedra. Rietveld structure refinement confirmed the coexistence of pseudocubic (Pm-3m) and rhombohedral (R3c) phases in AQ samples, with predominantly pseudocubic phase, while CS samples closely approximated the pseudocubic phase. The microstructure of the samples exhibits small average grain size distribution (<2 μm). Temperature-dependent dielectric measurements show strong frequency dispersion in the dielectric permittivity with broadened transition peaks. The ferroelectric studies reveal low Pr and Ec values. These observations suggest a ferroelectric relaxor-like behavior of the developed materials. Moreover, the permittivity peaks maxima (Tm) temperature corresponding to CS samples for 0.04<x < 0.07 is less than 390 °C at 10 Hz while it is above 400 °C for AQ samples. The results of our study reveal that AQ samples exhibit superior electrical and ferroelectric properties as compared to the CS samples. The AQ samples demonstrate improvements in Tm (>400 °C), d33(∼35 pC/N), Pr (∼4–11 μC/cm2), PS (∼8–21 μC/cm2), Ec (∼13–25 kV/cm) with reduced dielectric loss, and a better dielectric constant over a wide temperature range.

Investigation on structural, optical and electrical properties of BiFeO3:ZnO nano–micro particles–matrix composite

A new class of materials called matrix-nano composites has the ability to meet the needs of modern advanced applications and technology. To prepare the BiFeO3:ZnO composite, BiFeO3 nanoparticles were prepared using a low–cost sol–gel method, to which ZnO in its micron-sized form was added in varying concentrations of 5%, 10%, and 15%. The structural, morphological, and optical properties of the pure and composite materials were characterized using XRD, FESEM, EDAX, PL spectra, and UV-Visible spectroscopy. The dielectric properties of the pristine and composites were investigated at room temperature. The a.c. conductivity fit with Jonscher's power law and CBH model described the charge conduction behaviour in all pure and composite materials. The temperature-dependent dielectric and loss measurements showed a temperature dependent relaxation process. UV–vis and PL characterization show that the composite materials exhibited improved charge separation efficiency and wider band gaps with increasing BFO content.

Enhanced Piezoelectric, Ferroelectric, and Electrostrictive Properties of Lead-Free (1-x)BCZT-(x)BCST Electroceramics with Energy Harvesting Capability.

Next-generation electronics and energy technologies can now be developed as a result of the design, discovery, and development of novel, environmental friendly lead (Pb)-free ferroelectric materials with improved characteristics and performance. However, there have only been a few reports of such complex materials' design with multi-phase interfacial chemistry, which can facilitate enhanced properties and performance. In this context, herein, novel lead-free piezoelectric materials (1-x)Ba0.95 Ca0.05 Ti0.95 Zr0.05 O3 -(x)Ba0.95 Ca0.05 Ti0.95 Sn0.05 O3 , are reported, which are represented as (1-x)BCZT-(x)BCST, with demonstrated excellent properties and energy harvesting performance. The (1-x)BCZT-(x)BCST materials are synthesized by high-temperature solid-state ceramic reaction method by varying x in the full range (x = 0.00-1.00). In-depth exploration research is performed on the structural, dielectric, ferroelectric, and electro-mechanical properties of (1-x)BCZT-(x)BCST ceramics. The formation of perovskite structure for all ceramics without the presence of any impurity phases is confirmed by X-ray diffraction (XRD) analyses, which also reveals that the Ca2+ , Zr4+ , and Sn4+ are well dispersed within the BaTiO3 lattice. For all (1-x)BCZT-(x)BCST ceramics, thorough investigation of phase formation and phase-stability using XRD, Rietveld refinement, Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and temperature-dependent dielectric measurements provide conclusive evidence for the coexistence of orthorhombic + tetragonal (Amm2 + P4mm) phases at room temperature. The steady transition of Amm2 crystal symmetry to P4mm crystal symmetry with increasing x content is also demonstrated by Rietveld refinement data and related analyses. The phase transition temperatures, rhombohedral-orthorhombic (TR-O ), orthorhombic- tetragonal (TO-T ), and tetragonal-cubic (TC ), gradually shift toward lower temperature with increasing x content. For (1-x)BCZT-(x)BCST ceramics, significantly improved dielectric and ferroelectric properties are observed, including relatively high dielectric constant εr ≈ 1900-3300 (near room temperature), εr ≈ 8800-12900 (near Curie temperature), dielectric loss, tan δ ≈ 0.01-0.02, remanent polarization Pr ≈ 9.4-14 µC cm-2 , coercive electric field Ec ≈ 2.5-3.6kV cm-1 . Further, high electric field-induced strain S ≈ 0.12-0.175%, piezoelectric charge coefficient d33 ≈ 296-360 pC N-1 , converse piezoelectric coefficient ≈ 240-340 pm V-1 , planar electromechanical coupling coefficient kp ≈ 0.34-0.45, and electrostrictive coefficient (Q33 )avg ≈ 0.026-0.038 m4 C-2 are attained. Output performance with respect to mechanical energy demonstrates that the (0.6)BCZT-(0.4)BCST composition (x = 0.4) displays better efficiency for generating electrical energy and, thus, the synthesized lead-free piezoelectric (1-x)BCZT-(x)BCST samples are suitable for energy harvesting applications. The results and analyses point to the outcome that the (1-x)BCZT-(x)BCST ceramics as a potentially strong contender within the family of Pb-free piezoelectric materials for future electronics and energy harvesting device technologies.

Unveiling a hidden multiferroic state under magnetic fields in BaHoFeO4

In this paper, we report field-induced ferroelectricity in ${\mathrm{BaHoFeO}}_{4}$ in a narrow range of applied magnetic fields ($1.5\phantom{\rule{4.pt}{0ex}}\text{T}\ensuremath{\le}H\ensuremath{\le}5\phantom{\rule{4.pt}{0ex}}\text{T}$). Magnetization measurements reveal three magnetic anomalies, the first one at ${T}_{N}^{\text{Fe}}\ensuremath{\sim}52.8$ K, the second one at ${T}_{{N}_{2}}\ensuremath{\sim}36.4$ K, and the third one at ${T}_{N}^{\text{Ho}}\ensuremath{\sim}6.8$ K, corresponding to the antiferromagnetic ordering of ${\mathrm{Fe}}^{3+}$, a possible spin structure change of ${\mathrm{Fe}}^{3+}$, and the antiferromagnetic ordering of ${\mathrm{Ho}}^{3+}$ sublattices, respectively. Surprisingly, the heat capacity data did not show any anomaly at ${T}_{N}^{\text{Fe}}$ but exhibited a broad maximum at ${T}_{N}^{\text{Ho}}$. Below 40 K, isothermal magnetization measurements indicate a metamagnetic transition at 1.5 T. The temperature-dependent dielectric measurements performed below 1 T reveal two anomalies, around 6 and 36 K, corresponding to ${\mathrm{Ho}}^{3+}$ ordering and a possible change in the magnetic phase of the Fe sublattice. These anomalies disappear at higher magnetic fields, and a different dielectric anomaly appears above the metamagnetic transition with a broad asymmetric peak around 13 K (${T}_{P}$), which shifts to higher temperatures, reaches a maximum under 2 T, and then is suppressed further on increasing the magnetic field up to 9 T. A switchable electric polarization appears below 25 K and above the metamagnetic transition field ($H\ensuremath{\ge}1.5$ T). Intriguingly, the polarization disappears above 5 T. The presence of electric polarization in intermediate magnetic fields and its strong magnetic field dependence are interesting and make this material unique.

Temperature-dependent dielectric measurements and structural properties of barium stannate (BaSnO3)

Cubic perovskite BaSnO3, synthesized by solid-state reaction method, was structurally characterized using temperature-dependent X-ray and Raman spectroscopy studies along with room temperature neutron diffraction analysis. Here, we report the effect of temperature on the structural parameters of BaSnO3 in correlation with dielectric properties. Sample homogeneity and elemental composition were studied by scanning electron microscopy and energy dispersive X-ray spectroscopy methods. The compound maintains cubic symmetry even at high temperatures and exhibits gradual increase in unit cell volume owing to thermal expansion. To understand high temperature phase transition, if any, and capacitance behavior, high temperature dielectric measurements were carried out. High value of dielectric constant was obtained at low frequencies as the temperature was increased, which may be due to the presence of oxygen vacancies or the lone-pair effect.

The role of Pr3+, Pr3+-Y3+ and Pr3+-Y3+-Dy3+ ions substitutions on the electrical and dielectric properties of NiCo nanospinel ferrites

This study investigated the electrical and dielectric features for NiCo (Ni0.5Co0.5Fe2O4) NSFs, Pr-NiCo (Ni0.5Co0.5Pr0.1Fe1.9O4) NSFs, PrY-NiCo (Ni0.5Co0.5Pr0.1Y0.1Fe1.8O4) NSFs and PrYDy-NiCo (Ni0.5Co0.5Pr0.1Y0.1Dy0.1Fe1.7O4) NSFs have been synthesized hydrothermally. The microstructure of all compositions was characterized thru XRD, SEM, EDX, TEM and HR-TEM. XRD analyses proved the formation of cubic structure and the absence of any impurity. The cubic morphologies of all products have been confirmed by HR-TEM and SEM measurements. The chemical composition presented by EDX was matched with the predicted chemical composition. Temperature (T) and frequency (f) dependent electrical and dielectric measurements were made to evaluate ac/dc conductivities, dielectric constant/losses, and dissipation factor as well as Cole-Cole plots of impedance functions for all NiCo NSFs substituted with Pr3+, Pr3+Y3+ and Pr3+Y3+Dy3+-ions. The ac conductivity measurements confirmed that it obeyed power law rules, largely dependent on the ion substitutions in the host NiCo NSFs. The dielectric constant of NiCo NSFs leads to the usual dielectric distribution, which is strongly influenced by substituted Pr3+, Pr3+-Y3+ and Pr3+-Y3+-Dy3+ ions. Impedance analysis indicated that the conduction mechanisms in all samples were mainly due to grain-to-grain boundaries. The variation in dispersion factors with frequency, like Koop's phenomenological model, is generally attributable to the conduction mechanism in ferrites.

Field dependent energy density and induced relaxor ferroelectric to relaxor antiferroelectric property investigation in potassium modified NKBT – ST ceramics

Lead free 0.60 (Na0.5-xKxBi0.5TiO3) – 0.40 (SrTiO3) perovskite ferroelectric ceramics were synthesized effectively by a conventional solid-state reaction root. X – ray diffraction and Rietveld refinement revealed the co-existence of dual phase crystal symmetries for the ceramics around the morphotropic phase boundary in all samples. The coexistence of rhombohedral (R3c) and cubic (Pm3m) phases occurred up to the dopant concentration x = 0.07, succeeding a tetragonal (P4bm) with cubic (Pm3m) symmetries were observed for higher dopant concentrations x = 0.12 and 0.15 respectively. SEM micrographs indicate that the formation of well packed dense microstructure with the nonuniform distribution. Temperature dependent dielectric measurement provoke the dielectric relaxation at low temperature near at depolarization temperature (Td). And then, the incorporation of ST in NKBT host matrix triggers the shifting of Curie temperature (Tm) towards the low temperatures. A stable relaxor ferroelectric like behavior up to the dopant concentration x = 0.07, and antiferroelectric like relaxor behavior was triggered progressively up to x = 0.15 was observed through in P-E loop studies. The electric field dependent recoverable energy storage performance at room temperature was calculated and a significant energy storage density (Wrec) and energy storage efficiency (η) values noticed for x = 0.15 ceramic, which shows the x = 0.15 ceramic optimistic for energy storage applications in dielectric capacitors.

The structural and electrical properties of polyaniline carbon nanotubes (PANI-CNTs) composite

Carbon nanotubes (CNTs) doped polyaniline (PANI) nanocomposite was synthesized by chemical polymerization method in the presence of HCl medium. The structure of the PANI/CNTs composite was confirmed by X-ray diffraction (XRD) technique. The SEM results showed granular and tube like shape for PANI and CNTs respectively. The SEM characterization of PANI-CNTs composite revealed a uniform wrapping of CNTs by PANI forming a core-shell nanostructure. The temperature dependent dielectric measurements were performed in the frequency range of 0.1 kHz-1 MHz. Dielectric measurements revealed the strong interactions between PANI and CNT nanoparticles causing a beneficial effect on stability of the composites. The dielectric constant followed the Maxwell-Wagner interfacial polarization. The frequency dependent conductivity obeyed a power law of frequency. Temperature has an effect on dielectric constant values of composite sample. Heat treatment affected the dipole polarization by reducing the relaxation time and hence contributed to the enhancement of dielectric parameters. Dielectric properties of composites were found to be improved due to addition of carbon nanotubes, which can improve the formation of a more efficient network for charge transport mechanism in the base polyaniline matrix. The border between polyaniline and CNTs can play an important role in yielding a large dielectric constant in the nanocomposites.

Inverse exchange bias effects and magnetoelectric coupling of the half-doped perovskite-type chromites Gd0.5Sr0.5CrO3 and Gd0.5Ca0.5CrO3

The ${\mathrm{Cr}}^{4+}$ oxidation state with two electrons in the $\mathrm{Cr}\phantom{\rule{0.28em}{0ex}}3d$ shell is not often observed in perovskite-type oxides, as high pressures and temperatures are generally required to stabilize the octahedral coordination. Herein, we present a comparative study of the half-doped perovskite-type chromites ${\mathrm{Gd}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{CrO}}_{3}$ (GSCO) and ${\mathrm{Gd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{CrO}}_{3}$ (GCCO). Fifty percent of the Cr occurs in the ${\mathrm{Cr}}^{4+}$ oxidation state after high-pressure synthesis at 6 GPa and 1200 \ifmmode^\circ\else\textdegree\fi{}C. The materials were investigated using synchrotron x-ray diffraction, magnetization, heat capacity, and dielectric measurements. The diffraction patterns show that GSCO and GCCO crystallize in orthorhombic ($Pnma$) structures with different degrees of local lattice distortion. GSCO exhibits a long-range magnetic order at temperatures of $&lt;98\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, accompanied by magnetization reversal, suggesting that the magnetic ground state is ferrimagnetic. In contrast, GCCO displays antiferromagnetic characters at temperatures $&lt;\ensuremath{\sim}100\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. In addition, GSCO exhibits a crossover between conventional and inverse exchange bias effects at low temperatures ($&lt;50\phantom{\rule{0.28em}{0ex}}\mathrm{K}$). This is likely caused by asymmetric exchange Dzyaloshinskii-Moriya interactions between the Cr ions of different valences (+3 and +4). Furthermore, significant magnetoelectric coupling at the onset of the magnetic order is supported by temperature-dependent dielectric measurements.

A study on the electrical properties of flux grown 0.91PZN-0.09PT single crystals for high-performance piezoelectric and pyroelectric device applications

In the present work, large-size piezoelectric single crystals of 0.91[Pb(Zn1/3Nb2/3)O3]-0.09PbTiO3 (PZN-9PT) have been grown by high-temperature flux method. Rietveld refinement analysis of X-ray diffraction data demonstrates the existence of monoclinic [Cm and Pm] phases, further supported by electron diffraction studies. PZN-9PT single crystal shows broad and diffused dielectric response peaks at 354 K and 443 K with noticeable frequency dispersion identified from temperature-dependent dielectric measurements. The 001 oriented PZN-9PT elements sliced from the grown single crystals display a remnant polarisation (Pr) of 30 µC/cm2, saturation polarization (Ps) of 33 µC/cm2, and an enhanced piezoelectric strain of 0.3 %. In addition, the piezoelectric coefficients d33, d31 and electric field-induced strain d33∗ measured by the direct method is 2100 pC/N, 1650 pC/N and 2500 pm/V, respectively. The mechanism behind the enhanced piezoelectric properties of PZN-9PT is explained with reference to the stabilization of the monoclinic phase and polarization rotation mechanisms. Further, the pyroelectric coefficient, p measured to be 11.31 × 10−4 C/m2 K at room temperature and 51.22 × 10−4 C/m2 K at the ferroelectric to the paraelectric phase transition temperature. The enhanced piezoelectric and pyroelectric properties of PZN-9PT make them suitable for high-performance piezoelectric transducers, actuators at ambient temperature and pyroelectric sensors at elevated temperature, respectively.

Preparation and characterization of CdO-ZnO core shell nano particles: Prepared by two step wet chemical method

CdO–ZnO core-shell nanoparticles (CSN) were successfully synthesized by two step assisted chemical sol gel method. The structural properties of synthesized CSN have been analyze by X-ray diffraction (XRD) method, XRD pattern shows a uniform, homogenous phase formation of nano crystals. Microstructural properties of prepared CSN have been analyze by FESEM and HRTEM methods, Surface morphology of the CSN was investigated using FESEM, which shows dense growth and thin layer of ZnO shell over CdO core where as crystallinity of the CSN have been observed from HRTEM images, HRTEM reassures the particle size as obtained from XRD analysis. The optical properties and optical band gap of CSN is obtained from UV–Visible spectroscopy. Raman modes obtained from Raman spectroscopy distinctly identify the CdO and ZnO phonon vibrational modes. The electrical properties have been investigated by temperature dependent dielectric measurement. Moreover, the impedance behavior at different temperature has been investigated by impedance spectroscopy.

Effect of irradiation on pyroelectric and electrocaloric parameters in lead-free relaxor ferroelectric ceramic

Ferroelectric materials have a renaissance due to various photosensitive characteristics. In this study, temperature-dependent dielectric, impedance, and ferroelectric measurements were carried out on lead-free Ba0.6(Bi0.5Li0.5)0.4TiO3 (BBLT) ferroelectric ceramic under the dark and exposure of monochromatic 405 nm light conditions. Profound analysis of complex impedance spectroscopy shows a noticeable reduction in bulk capacitance, relaxation time, and constant phase element parameters under illuminated conditions. Relevant phenomenological approaches towards modified Cole−Cole models confirm that the light induces photogenerated nonequilibrium charge carriers. Thus, the trapped charges alter the internal electric field distribution energy. Under illumination, the enhanced polarization and corresponding pyroelectric coefficient enhanced by 40 % and ~260 % at 5 Hz and 10 Hz, respectively, at 20 ℃ were observed. The cross-coupled Electrocaloric (EC) parameters ∆T and ∆S enhanced 600 % and 571 % at 10 Hz, respectively, and 219 % and 218 %, at 5 Hz respectively at 20 ℃ under illumination. This study provides a comprehensive understanding and new insights into the light-dependent dielectric, ferroelectric, pyroelectric and electrocaloric mechanisms in BBLT electroceramics, which encourages the design of modern thermal sensor devices.

Enhanced relaxor behavior and high energy storage efficiency in niobium substituted (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics

The microstructure, dielectric properties, relaxor behavior, and energy storage efficiency of un-substituted and niobium (Nb) substituted (Ba0.85 Ca0.15)(Zr0.1 Ti0.9) 1-x NbxO3 (for x = 0, 0.02 and 0.05) samples prepared by the solid-state reaction method has been studied in detail. All the samples exhibited perovskite structure with no trace of impurity. Composition-dependent phase transition was also observed on the addition of Niobium. At room temperature, the co-existence of rhombohedral and tetragonal phases is observed in the unsubstituted samples. As the composition changes from x = 0.02 to x = 0.05, a structural change from tetragonal to cubic is observed. A remarkable reduction in grain size, from 90 μm (for x = 0) to 1.21 μm for (x = 0.05), is observed with the addition of Niobium. This result suggests that Niobium acts as a grain growth inhibiter in barium calcium zirconium titanate (BCZT) ceramics. The effect of Niobium on transition temperature is studied from the temperature-dependent dielectric permittivity graph. It was clear that the transition temperature shifted to a lower temperature region, and for x = 0.05, at a very low temperature (−23 °C/250 K) the tetragonal to cubic transition was observed. At x = 0.05, the temperature-dependent dielectric permittivity showed a broadened curve, indicating a diffuse phase transition. The diffuse phase transition in Nb substituted samples is explained by Uchino and Nomura modified Curie Weiss law.Moreover, the observations on temperature-dependent dielectric permittivity measurements at various frequencies suggest that the substitution of Nb5+ induces relaxor behavior. The energy storage efficiency of unsubstituted and Nb substituted samples was calculated from the polarization versus electric field graph. A high storage efficiency of 84% was obtained for the Nb substituted sample (x = 0.05) at 12 kV cm−1. Enhanced relaxor behavior and increased storage efficiency were observed in (Ba0.85 Ca0.15)(Zr0.1 Ti0.9) 1-x NbxO3 at x = 0.05. Thus we suggest that these are promising materials for energy storage applications.