P4mm Phase Research Articles

Pressure-induced superconductivity and phase transition in PbSe and PbTe

Abstract The IV-VI semiconducting chalcogenides are a large material family with distinct physical behavior. Here, we systematically investigate the effect of pressure on the electronic and crystal structure in PbSe and PbTe by combining high-pressure electrical transport and synchrotron x-ray diffraction (XRD) measurements. The resistivity of PbSe and PbTe changes dramatically under high pressure and a non-monotonic evolution of ρ(T) is observed. Both PbSe and PbTe are found to undergo semiconductor-metal transition upon compression and show superconductivity under higher pressure. The structural evolutions from the Fm-3m to Pnma phase and then to the Pm-3m phase in PbSe are verified by the x-ray diffraction. The present findings reveal the internal correlation between the structural evolution and the physical properties in lead chalcogenides.

Impedance Spectroscopy of Lanthanum-Doped (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 Ceramics

This study examines the effects of La3+ doping on (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3(PBZT) ceramics, which were synthesized using the conventional solid-state reaction method. X-ray diffraction analysis confirmed that the PBZT structure, including PBZT doped with La3+ at concentrations x = 1 at.% and x = 2 at.%, exhibited a rhombohedral (R3c) space group, while higher doping levels of x = 3 at.% and x = 4 at.% led to a dominant cubic (Pm-3m) phase with approximately 30% of a remnant rhombohedral component. Scanning electron microscopy (SEM, JEOL JSM-7100F TTL LV, Jeol Ltd., Tokyo, Japan) and energy dispersive X-ray spectroscopy (EDS) were utilized to investigate the structure and morphology of these ceramics. The findings indicated that the chemical composition of the ceramic samples closely corresponded to the initial stoichiometry of the ceramic powder. An increase in the amount of lanthanum results in a decrease in the average grain size of the ceramics. The electrical properties were further evaluated using complex impedance spectroscopy (IS) over a range of temperatures and frequencies, as well as temperature dependence of DC conductivity. The similarity in the changes in activation energy for DC conductivity and grain boundary conductivity, caused by lanthanum ion modification, allows for the conclusion that grain boundaries are the primary microstructural element responsible for conductivity in these materials.

Dual zinco-phobic/-philic ferroelectric nanorods coated mesh for stable Zn anode

Aqueous Zn-ion batteries are emerging as a promising option for energy storage systems due to their safety and environmental benefits. However, their stability and reversibility are often hindered by dendrite growth and interfacial side reactions. In this study, we introduce an innovative strategy to address these issues by engineering an artificial interfacial layer (AIL) on Zn anode surface. This AIL is composed of a dual zinco-phobic/-philic ferroelectric nanorods (FE NRs) mesh, which contrasts with the traditional BaTiO3 nanoparticles. The BTO NRs, particularly those with exposed P4/mmm (100) and (211) facets enriched with oxygen vacancy, facilitate a partial phase transition from the FE tetragonal P4mm phase to the paraelectric tetragonal P4/mmm phase, thereby creating dual zinco-phobic/-philic sites. Additionally, the integration of microchannels within the FE BTO NRs mesh can efficiently modulate the electric field distribution and Zn2+ concentration, leading to a more uniform Zn deposition, as conformed by electrochemical simulations. The Zn anode coated with the FE BTO NRs mesh exhibits impressive performance, achieving an ultralong cycle life of 3050 h at 1 mA cm−2 and 1mAh cm−2. It sustains a Coulombic efficiency exceeding 99.8 % over 2000 cycles, highlighting its exceptional reversibility. These findings underscore the potential of the dual zinco-phobic/-philic FE NRs mesh in overcoming the challenges faced in aqueous metal-ion batteries, showcasing its versatility and the significant performance enhancements it can offer.

An in-depth comparison of dielectric, ferroelectric, piezoelectric, energy storage, electrocaloric, and piezocatalytic properties of Ba0.92Ca0.08Zr0.09Ti0.91O3 and Ba0.92Ca0.08Sn0.09Ti0.91O3 piezoceramics

The futuristic technology demands materials exhibiting multifunctional properties. Keeping this in mind, an in-depth investigation and comparison of the dielectric, ferroelectric, piezoelectric, energy storage, electrocaloric, and piezocatalytic properties have been carried out on Ba0.92Ca0.08Zr0.09Ti0.91O3 (BCZT) and Ba0.92Ca0.08Sn0.09Ti0.91O3 (BCST) lead-free compounds synthesized through the conventional solid state reaction method. Further, the Rietveld refinement against the XRD patterns affirmed the coexistence of orthorhombic (Amm2) and tetragonal (P4mm) phases at room temperature for both compounds. While BCZT compound demonstrated remarkable dielectric, piezoelectric, and piezocatalytic characteristics with maximum dielectric constant () ≈ 13304 near the Curie temperature ( ≈ 105 °C), converse piezoelectric coefficient ≈ 609 pm V-1 , power density () ≈ 89.71 KW cm-3 at room temperature, and 82.7 % Rhodamine B (RhB) dye degradation capability; on the other hand, BCST compound exceled in superior energy storage density () ≈ 191.8 mJ cm-3 with efficiency η ≈ 73.26% near room temperature and enhanced electrocaloric properties with adiabatic temperature change ≈ 0.980 K, isothermal entropy change ≈ 1.15 J Kg-1K-1 and a higher electrocaloric responsivity ) ≈ 0.49 K mm kV-1. These distinctions arise from the difference in ionic radii, lattice distortion, and the electronic configurations of the dopant ions, leading to a greater polarization change and a lower coercive electric field in the BCST ceramic. The outcome of the present study provides valuable insights for selecting a dopant tailored compound for specific application and underscores the potential of such ceramics in energy storage, piezocatalysis, and the development of advanced solid-state cooling devices for future applications.

Large electrocaloric effect across the non-hysteretic electrostructural phase transition in lead-free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 ceramics

Structural, dielectric, and electrocaloric properties were investigated in Pb-free ceramic (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 (BCST), synthesized using solid-state sintering method. Rietveld refinement of room temperature XRD data revealed the existence of pure perovskite tetragonal (P4mm) phase. Temperature-dependent XRD analyses confirmed a structural transition from tetragonal to cubic phase near 380 K. Temperature-dependent dielectric constant (εr) and specific heat capacity (Cp) confirmed the presence of thermal hysteresis in two phase transitions near 233 ± 10 K and 254 ± 10 K, and a non-hysteretic behavior at the Curie temperature (TC∼373 ± 10 K). A comprehensive Raman study corroborated the existence of phase transitions. Electrocaloric properties were determined using indirect method utilizing the non-hysteretic nature across TC. A large adiabatic temperature change of |∆T| = 0.52 K, isotropic entropy change |∆S| = 0.68 J/kg.K, electrocaloric coefficients, |∆T/∆E |= 0.311 K.mm/kV and |∆S/∆E| = 0.41 J.mm/K.kg.kV were obtained at 380 K for an electric field of 16.7 kV/cm. Obtained value of |∆T/∆E| is relatively good, reported among other BaTiO3-based ceramics.

Effect of different ionic valence state doping on the structure and characteristic of BiFeO3‐BaTiO3‐based ceramics

AbstractBiFeO3‐BaTiO3‐based ceramics are promising multiferroic materials for a wide range of applications. In this paper, the effects of different ionic valence state((Ga0.5Ta0.5)4+, Ta5+) doping on the structure and properties of 0.73BiFeO3‐0.27BaTi1‐y(Ga1‐xTax)yO3 ceramics were investigated. X‐ray diffraction analysis showed that all samples were determined by rhombohedral R3c phase and tetragonal P4mm phase. A frequency‐independent dielectric anomaly with obvious thermal hysteresis was detected in all samples, indicating the first‐order ferroelectric phase transition, and the Curie temperatures were all above 600°C. The ferroelectric analysis found that the doping of donor element Ta reduced the coercive field, with a slight decrease of remanent polarization, which can be attributed to the soft effect of Ta element. Meanwhile, the magnetic properties were enhanced for all samples, with a maximum in 15T (x = 1, y = .015) sample, where Mr = .13 emu/g. According to relevant analysis, high‐valence element substitution can enhance the magnetic properties and reduce the coercive field of BiFeO3, while low‐valence element substitution can reduce dielectric loss. This result points out a way for us to choose appropriate doping elements to improve the performance of BiFeO3 ceramics.

Orthorhombic-tetragonal phase coexistence and enhanced piezoelectric properties at room temperature in Zn and Ta modified (Ba0.95Ca0.05)(Zr0.05Ti0.95)O3 ceramics through the synergistic effect of lattice distortion.

This study provides a fundamental understanding of the enhanced piezoelectric properties in ABO3 perovskite based lead-free piezoelectric materials. For this we synthesized (Ba0.95Ca0.05)(Zr0.05Ti0.95-x (Zn1/3Ta2/3) x )O3((1 - x)BCZT-(x)ZT) (x = 0.00, 0.005, 0.01, and 0.02) solid solutions exhibiting high piezoelectric response. The (1 - x)BCZT-xZT materials are synthesized by a high-temperature solid-state ceramic reaction method by varying x in the full range (x = 0.00-0.02). In-depth exploratory research is performed on the structural, dielectric, ferroelectric, and piezoelectric properties of (1 - x)BCZT-(x)ZT 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+, Zr2+ and Ta5+ are well dispersed within the BaTiO3 lattice. For all (1 - x)BCZT-(x)ZT ceramics, thorough investigation of phase formation and phase-stability using XRD, Rietveld refinement, Raman spectroscopy, 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 c/a ratio of the tetragonal phase greatly influenced the electric properties of the ceramics. The c/a ratio of the tetragonal phase increases from 1.0112 for x = 0 to 1.0157 for x = 0.005 and subsequently decreases to 1.0038 for x = 0.02. When the c/a of the tetragonal phase reaches its maximum value, the ceramic with x = 0.005 has the best piezoelectricity (d 33 ∼ 297 pC N-1). The calculated degree of relaxation (γ) increases with the increase in BZT content, indicating that the BCZT-xBZT ceramics are ferroelectric materials with diffuse phase transition. Main dielectric, piezoelectric and ferroelectric parameters of (1-x)BCZT-xZT ceramics were optimized around x = 0.005 with a high piezoelectric coefficient (d 33 = 297 pC N-1), a remnant polarization (P r = 7.58 μC cm-2), spontaneous polarization (P s = 10.25 μC cm-2) and a high dielectric constant (ε max,T c = 4449 at T c and 2330 near RT) at 1 kHz, indicating promising applications for lead-free piezoelectric ceramics.

Effect of excess Bi2O3/PbO on the structural and electrical properties of ternary 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3 ceramics

The ternary 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3:x(Bi2O3/PbO) [x = 0, 1, and 2 wt%] ceramics were synthesized via solid-state sintering technique. The impact of excess addition on structural and electrical properties was investigated. PXRD results confirmed the diffusion of excess addition in the 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3 (BNPZT) lattice, exhibiting the perovskite structure with major rhombohedral (R3c) and minor tetragonal (P4mm) phases. The microstructure of the samples exhibits average grain size distribution (<8 μm). The temperature and frequency-dependent dielectric measurement revealed the relaxor-like ferroelectric behaviour and curie temperature (Tc∼290 °C) observed in BNPZT:1 Pb ceramics. The improved remnant polarization (Pr∼23.47 μC/cm2) and coercive field (Ec∼16.13 kV/cm) were obtained in BNPZT:2 Pb ceramics. The enhanced piezoelectric charge coefficient (d33∼ 496 pC/N) and maximum strain (Smax∼0.12 %) were obtained for BNPZT. The least asymmetric factor (γs) illustrates the lower concentration of inherent defects in BNPZT:1(Bi/Pb) ceramics. This study provides insight into microstructural and electrical properties tuning and paves the way for designing piezoelectric materials.

Significantly enhancing piezoelectric temperature stability of BNT-based ceramics by constructing the successive ferroelectric-relaxor phase transition

Bi0.5Na0.5TiO3 (BNT)-based piezoceramics with the morphotropic phase boundary MPB are confronted with some critical challenges for practical applications, such as the low depolarization temperature Td, the poor thermal shock resistance and the high fluctuation of the real-time piezoelectric coefficient d33. Herein, an ingenious strategy that integrating quenching process and successive ferroelectric-relaxor phase transition is proposed to enhance piezoelectric temperature stability of BNT-based ceramics. The multilayer ceramic composites (0.93Bi0.5Na0.5TiO3-0.07BaTiO3/0.89Bi0.5Na0.5TiO3-0.11BaTiO3/0.85Bi0.5Na0.5TiO3-0.15BaTiO3-0.2 g/0.25 g/0.15 g-Q, abbreviated as BNT-7/11/15BT-0.2 g/0.25 g/0.15 g-Q, the Q refer the quenching process and the 0.2 g/0.25 g/0.15 g refers the mass of each layer) feature the relatively large d33 (130pC/N) and near the Curie point Td (244℃), which jumps out of the d33-Td trade-off boundary of BNT-based ceramics. Besides, the BNT-7/11/15BT-0.2 g/0.25 g/0.15 g-Q ceramic composite also shows the superior thermal shock resistance and decent temperature stability of real-time d33 over the temperature region from 25℃ to 235℃. Enhanced piezoelectric temperature stability should be attributed to the development of tetragonal P4mm and P4bm phase gradients caused by the successive ferroelectric-relaxor phase transition and the development of bamboo-shaped domain based on Ba2+ diffusion layer. In addition, the relatively large d33 stems from the coexistence of rhombohedral R3c phase and tetragonal P4bm and P4mm phases and the formation of lamellar domain. Therefore, this strategy provides a good design methodology for the practical application of BNT-based materials.

Crystal structure prediction and non-superconductivity of N-doped LuH3 at near ambient pressure

Lanthanide polyhydrides, which have attracted the attention of researchers, are considered as a potential candidate material for high-temperature superconductivity. Especially, it is reported that N-doped LuH3 exhibits near ambient superconductivity recently. It has attracted attention to room temperature superconductivity of ternary Lu-N-H systems at near ambient pressure. Here, we constructed a LuNH3 (N-doped LuH3) compound to predict the crystal structural at relatively low pressures. We found a stable ternary LuNH3 structure with a tetragonal P4mm phase under 5 GPa. In addition, our calculations show that the P4mm LuNH3 structure does not exhibit superconductivity down to 0.3 K at near ambient pressure due to the H atoms hardly contribute to acoustical phonons.

High-throughput calculation for superconductivity of sodalite-like clathrate ternary hydrides MXH12 at high pressure

Inspired by the experimental synthesis of the first theoretically predicted clathrate hydride CaH6 with high Tc of 215 K at 172 GPa, we designed a series of Pm-3m phase ternary hydrides MXH12 and performed high-throughput calculations. Ten compounds were discovered, among which YHfH12, YThH12, ScZrH12, and LaThH12 show good superconductivity with critical temperatures above 150 K. LaThH12 and YCeH12 can be dynamically stable at a minimum of 100 GPa. Aiming at a comprehensive description of the H24 cage that dominates the superconductivities of MXH12, we proposed a variable AE, which is defined as the average ELF value at the center of all the H–H bonds in the cage-like hydrides. Combining the AE with the contribution of the H element to the total DOS at the Fermi level, we constructed a simple liner model (called the AE model) by fitting the data of hydrides MXH12. The mean absolute error is 11.7 K suggesting a strong linear correlation between AE and Tc. Furthermore, the AE model can be generalized to predict the superconductivity of other cage-like hydrides such as LaH10 (or YH10) with H32 cage, YH9 (or CeH9) with H29 cage, and more complex cage-like hydrides such as La4H23 and LaBeH8. The AE model could estimate the Tc of clathrate hydrides with small computational cost and provide reliable reference for further high-throughput calculations and experimental research.

Antiferroelectric-like BiFeO3-SrTiO3 based ceramics with high breakdown strength and energy-storage density

Herein, an outstanding excellent energy storage performance (ESP) (Wrec∼4.4 J/cm3; η∼72%; ΔP = 38.1 μC/cm2) was obtained in environmentally friendly 0.52BiFeO3-0.4SrTiO3-0.08NaNbO3 lead-free ceramic. First, the addition of NaNbO3 (NN) lead to composition and charge disorder of A- and B- sites, generating random electric field that induce the emergence of small-sized polar nano-regions (PNRs) to enhance ΔP (Pmax-Pr). Rietveld refinement analysis showed that introducing NN reduces the content of polar R3c phase from 81.8% to 24.4%, and the non-polar Pm3m phase increased. When x ≥ 0.08, the antiferroelectric-like double P-E loops were acquired due to field-induced phase transition, and further lower Pr and Ec were obtained. Then, the introduction of NN greatly improved the breakdown strength of BFO-STO ceramics. That is, enhances electrical homogeneity, increases energy gap (Eg) and refines grain size (from 1.05 to 0.75 µm). Through domain engineering, antiferroelectric-like design and other multi-factors to achieve the optimization of ESP, providing a feasible strategy for lead-free pulse energy storage capacitors. Additionally, the good temperature (20–120 °C) and frequency (1–100 Hz) stability acquired to less than 15% in favor of practical applications.

Effect of bismuth deficiency with K substitution for Na on piezoelectric properties and crystal structure of Bi0.5−x(Na0.8−yK0.2+y)0.5TiO3–3x/2 (0 ≤ x ≤ 0.015, 0 ≤ y ≤ 0.1) ceramics

The piezoelectric properties and crystal structure of Bi0.5−x(Na0.8−yK0.2+y)0.5TiO3–3x/2 (0 ≤ x ≤ 0.015, 0 ≤ y ≤ 0.1) ceramics were characterized in this study. The crystal-structure refinement for Bi0.5−x(Na0.8K0.2)0.5TiO3–3x/2 was carried out using synchrotron X-ray diffraction data and Rietveld analysis and revealed the coexistence of rhombohedral (R3c) and tetragonal (P4mm) phases for the compositions with 0 ≤ x ≤ 0.015, although the fraction of these phases was almost independent of the composition x (49% for the rhombohedral phase and 51% for the tetragonal phase at x = 0.015). The Bi deficiency led to an increase in the lattice distortion of rhombohedral phase and a decrease in the that of tetragonal phase. The piezoelectric constant (d33) value decreased from 151.5 to 120.6 pC/N as x was increased from 0 to 0.015, and a shift of the depolarization temperature to higher temperatures was also confirmed by in situ d33 measurements. These results are attributed to an increase in the lattice distortion of rhombohedral phase enhanced by the Bi deficiency. The K substitution for Na in Bi0.485(Na0.8−yK0.2+y)0.5TiO2.9775 led to the formation of a morphotropic phase boundary (MPB) in the composition range 0 ≤ y ≤ 0.06, resulting in an increase in the fraction of the tetragonal phase. Although a decrease in the mechanical quality factor (Qm) was observed for K-rich compositions, the highest d33 value of 195.4 pC/N with a mechanical coupling factor of 32.9% was obtained for the Bi0.485(Na0.76K0.24)0.5TiO2.9775 (y = 0.04) ceramic because of the enhancement of the tetragonality in the MPB region, resulting in the onset of depolarization at ∼170 °C.

Stability and mechanical, thermodynamic and optical properties of WC polytypes and the TiC-WC solid solutions: A first-principles study

First-principles calculations and molecular dynamics (FPMD) simulations in the constant number of particles – pressure – temperature (NPT) ensemble were used to investigate the phase stability, phase diagram, electronic and phonon structures, chemical bonding, mechanical, thermodynamical and optical properties of various tungsten carbide polytypes as well as the hexagonal (α) and cubic (β) Ti1-xWxCy solid solutions. The known α-WC (P-6m2) and β-WCy (Fm-3m) polytypes and eight hypothetical ones were studied. Gibbs free energy calculations predicted the α-WC → β-WCy and α-WC → tP4-129 (P4/nmm) phase transitions. The P-6m2 → Fm-3m → I41md, Fm-3m → P4/nmm and P-6m2 → Pm-3m phase transformations were revealed during FPMD simulations of: α-WC at T = 2500 K, β-WC at T = 100 K, and α-WC at T = 2500 K and P = 500 GPa, respectively. It is found that the known α-polytype and new tI8-109 (I41md), oP12-25 (Pmm2), hP4-194 (P63/mmc), hP8-194 (P63/mmc), cP2-221 polytypes are ultraincompressible and ultrastiff materials, and exhibit the highest hardness (29–38 GPa), fracture toughness (4.7–7.2 MPa m1/2) and Debye temperature (615–663 GPa). Other characteristics of the WC polytypes, namely, the stress-shear strain curves, dielectric function, reflectivity spectra, heat capacity and spatial distribution of the elastic moduli, were calculated and discussed. The stability, mechanical properties and lattice parameter of β-WCy and Ti1-xWxCy as functions of composition were studied. The binodal and spinodal for Ti1-xWxC were calculated. The calculated characteristics are compared with available experimental data and used for their interpretation.

Dielectric properties of mixed nanocomposites BaTiO&lt;sub&gt;3&lt;/sub&gt;–SrTiO&lt;sub&gt;3&lt;/sub&gt;

The dielectric properties of (1 – x)BaTiO3–xSrTiO3 (x = 0.0; 0.25; 0.50; 0.75 and 1.00) mixed nanocomposites, obtained by sintering the initial components at a temperature of 1273 K for 5 hours, have been studied within the temperature range of 100–500 K. X-ray analysis, performed at room temperature, showed that the composites are formed by BaTiO3 (P4mm) and SrTiO3 (Pm-3m) crystallites and do not contain Ba(1 – х)SrхTiO3 solid solutions. A decrease in the temperatures of the Amm2 → P4mm → Pm-3m phase transitions in barium titanate particles with an increase in the SrTiO3 concentration in the composite was found.

Overview of the Structural, Electronic and Optical Properties of the Cubic and Tetragonal Phases of PbTiO3 by Applying Hubbard Potential Correction.

We have performed a systematic study resulting in detailed information on the structural, electronic and optical properties of the cubic (Pm3¯m) and tetragonal (P4mm) phases of PbTiO3 applying the GGA/PBE approximation with and without the Hubbard U potential correction. Through the variation in Hubbard potential values, we establish band gap predictions for the tetragonal phase of PbTiO3 that are in rather good agreement with experimental data. Furthermore, the bond lengths for both phases of PbTiO3 were assessed with experimental measurements, confirming the validity of our model, while chemical bond analysis highlights the covalent nature of the Ti-O and Pb-O bonds. In addition, the study of the optical properties of the two phases of PbTiO3, by applying Hubbard' U potential, corrects the systematic inaccuracy of the GGA approximation, as well as validating the electronic analysis and offering excellent concordance with the experimental results. Therefore, our results underline that the GGA/PBE approximation with the Hubbard U potential correction could be an effective method for obtaining reliable band gap predictions with moderate computational cost. Therefore, these findings will enable theorists to make use of the precise values of these two phases' gap energies to enhance PbTiO3's performance for new applications.

Effect of Sr-doping on structural, morphological and dielectric properties of BaTi0.93Sn0.07O3 ferroelectric ceramics

In this report, we studied the Ba1-xSrxTi0.93Sn0.07O3 (x = 0.00, 0.10, 0.20, and 0.30) Perovskite ceramics produced by solid-state reaction (SSR) method and investigated their structural, morphological and dielectric properties by XRD, SEM, and LCR meter respectively. The Rietveld refinement of the XRD pattern confirms the samples crystallize in the Perovskite structure and transform from tetragonal for x = 0.0 to the co-existence of both cubic (Pm-3m) and tetragonal (P4mm) phases near room temperature for x ≥ 0.10. The Williamson-Hall (W–H) method has been used to determine the crystallite size and microstrains from the XRD peaks analysis, which showed the crystallite size value decreases with increased doping with Sr. The surface morphology shows the formation of ceramic grains with well-defined grain boundaries, as well as a decrease in grain size with an increase in the doping ratio. Moreover, the elemental ratio of doped ions was confirmed by EDS. The dielectric properties (έ, and tanδ) were studied as a function of temperature (20–150 °C) and a frequency (20 kHz - 3 MHz). The values of the dielectric constant έ decrease with the higher the frequency used. A diffuse phase transition was observed when doped with Sr. Where doping with Sr causes outstanding stability of έ values, which is evident by the flattening the dielectric constant curve, addition to increasing the dielectric constant values over range studied temperatures.

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.

Structural mechanisms of large piezoelectric responses in BiFeO3-PbTiO3 based solid-solution ceramics

Achieving large piezoelectric response and high Curie temperature, simultaneously, are of great demand but have been rarely achieved in BiFeO3-PbTiO3 (BF-PT) based morphotropic phase boundary (MPB) systems. In this work, in-situ synchrotron x-ray diffraction and transmission electron microscopy were carried out in BF-PT-0.19Ba(Zr,Ti)O3 high-temperature piezoceramic, a recently reported MPB composition with high piezoelectric coefficient, to elucidate the underlying structural mechanism. A field induced irreversible transition from tetragonal (T) P4mm phase to rhombohedral (R) R3c phase is identified although R and T phases are still coexisted after poling. This induces the significantly enhanced irreversible domain switching of both R and T phases and the reversible domain switching of R phase but only a slightly enhanced reversible switching of T phase of as compared with other BF-PT-x Ba(Zr,Ti)O3 MPB compositions, leading to the significant increase of lattice strain up to ∼0.15% but only a slightly increase of strain from extrinsic domain switching due to the strong coupling between lattice strain and domain switching in both R and T phases, although the strain contribution seems to be composition independent after the field induced irreversible phase transition. The present study demonstrates a new performance enhancement mechanism to design the high-performance BF-PT based high-temperature piezoelectric ceramics in terms of the different roles of R and T phases within MPB.

Microstructural and high-temperature dielectric, piezoelectric and complex impedance spectroscopic properties of K0.5Bi0.5TiO3 modified NBT-BT lead-free ferroelectric ceramics

Solid solutions (1-x-y)(Na0.5Bi0.5)TiO3-xBaTiO3-y(K0.5 Bi0.5)TiO3 with (x (mol.%) = 0, 7 and 100); y(mol.%) = 0, 20 and 100) compositions have been prepared by a conventional solid-state reaction method, and their structure, dielectric properties and depolarization temperature have been examined. At room temperature, X-ray diffraction (XRD) patterns reveal that the crystalline structure of the ceramics was perovskite. The morphotropic phase boundary (MPB) of the ternary system lying between rhombohedral (R3c) and tetragonal (P4mm) phases is in the range of (x (mol.%) = 7 and y (mol.%) = 20). The Raman-active modes for 0.73NBT-0.07BT-0.20KBT were separated and identified under the framework of group theory. SEM micrographs illustrate the quasi-uniform distribution of the grains, which are compact. The dielectric properties of the ceramics were studied in the frequency range of 1 kHz–100 kHz from ambient temperature to 600 °C. Dielectric measurements indicate that all ceramics show a diffuse phase transition near the temperature (Tm) for diffusivity of the order of 1.4–1.7 and a shift of (Tm) towards high temperatures. The resistance and capacitance of the various contributors (grain and grain boundary) in our samples are also discussed using a brick-layer model. Excellent piezoelectric properties for d33 = 146 pCN−1 and electromechanical coupling factors kp = 29.4% were observed at morphotropic phase boundary (MPB), which was assumed to be associated with the coexistence of rhombohedral and tetragonal phases and accurate grain size. This work establishes a new approach for improving lead-free piezoelectric ceramics based on 0.73NBT-0.07BT-0.20KBT.