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High-entropy ceramics have garnered significant attention in recent years owing to their exceptional properties and structural diversity. In this work, single-phase medium/high entropy ceramics, namely (Ca 0.2 Sr 0.4 Ba 0.4)(Zr 0.5 Ti 0.5)O 3 and (Ca 0.2 Sr 0.4 Ba 0.4)(Zr 0.1 Ti 0.9)O 3 , were successfully designed and prepared utilizing Spark Plasma Sintering (SPS). A comprehensive investigation was conducted into the phase structure, microscopic morphology, dielectric properties, and thermal behavior of these ceramics. It was observed that all ceramics maintained a cubic perovskite structure (space group: Pm 3 ‾ m), and the introduction of multi-element doping rendered them more stable across a wide frequency and temperature range. Notably, (Ca 0.2 Sr 0.4 Ba 0.4)(Zr 0.5 Ti 0.5)O 3 exhibited remarkably low dielectric loss (0.0001 at 1 kHz) at room temperature, along with excellent dielectric temperature stability (25–400 °C). By reducing the zirconium concentration in (Ca 0.2 Sr 0.4 Ba 0.4)(Zr 0.1 Ti 0.9)O 3 , a slight decrease in dielectric temperature stability was observed (25–350 °C); however, it demonstrated lower thermal conductivity (0.41 W/(m·K), 1200 °C) and maintained good high-temperature stability. The discovery highlights the promising practicality of both ceramics for high-temperature dielectric applications. [ABSTRACT FROM AUTHOR]

Sub-micrometer-sized (0.33 μm) polycrystalline powders of calcium copper titanate (CCTO) were synthesized via the solgel method. Compacted calcined powders were sintered at 900 °C/2h to obtain porous (<80% density) pellets. Subsequently, ZnO or SnO2 pastes (∼10 μm grain size) were smeared on either side of the pellets and sintered at 1100 °C/15 h, which yielded dense (>95% density) ceramics. X-ray structural investigations revealed the presence of ZnO or SnO2 traces in the bulk of the CCTO ceramics. Scanning electron microscopy and energy dispersive spectroscopic studies confirmed the diffusion and the segregation of these oxides at the grain boundaries. The dielectric and varistor properties of the ZnO or SnO2 diffused samples were found to be superior to that of pristine CCTO ceramics. For instance, the dielectric constant (ɛ′) of ZnO diffused ceramics exhibited a value as high as 2.4 × 104 (1 kHz, at room temperature) and a dielectric loss (D) of 0.059. Similarly, SnO2 diffused ceramics exhibited a dielectric constant of 2.7 × 104 (1 kHz, at room temperature) associated with a dielectric loss of 0.047. The figure of merit of varistor performance, i.e., nonlinear coefficient (α = 10.6), of the SnO2 diffused sample is significantly higher than that of ZnO diffused (α = 7.4) and pristine CCTO (α = 4.5) ceramics. The dielectric data obtained for both the pristine and ZnO or SnO2 diffused ceramics were rationalized by invoking Cole–Cole analysis. The thermal activation energy was estimated from the temperature-dependent dielectric data besides current (I)–voltage (V) characteristics. Equivalent circuit modeling of the Nyquist plots demonstrated that the inclusion of ZnO and SnO2 layers in CCTO ceramics remarkably improved the grain boundary resistance (Rgb) by 5-fold and 20-fold, respectively, which resulted in making CCTO a better dielectric. This methodology of fabricating ceramics via interfacial engineering could pave the way for obtaining superior CCTO ceramics associated with exotic functional properties. [ABSTRACT FROM AUTHOR]

Sodium bismuth titanate‐based materials are expected to be an alternative candidate to lead‐based ceramic materials due to their excellent electrical properties. However, the low depolarization temperature (Td) limits their practical application. In this work, the phase structure evolution and microstructure of 0.9(0.4Na1/2Bi1/2TiO3–0.6BiFeO3)–0.1BaTiO3: xZnO (x = 0.01, 0.03, 0.05, and 0.07) (abbreviated as 100xZnO) composite ceramics are investigated, and their piezoelectric properties are improved by combination of constructing 0–3 type composites and quenching treatment technology. The addition of ZnO can increase both Td and d33 because ZnO can enhance the lattice distortion of rhombohedral phase and lead to the increase in ferroelectric order. Specifically, the optimum composition x = 0.03 obtains the d33 value of 106 pC/N (25°C), which retains 84% of the value at room temperature up to 240°C. And the quenching technology further enhances the ferroelectric order and increases Td, which is up to 280°C for x = 0.03. [ABSTRACT FROM AUTHOR]

The present study focuses on the synthesis and characterization of rare-earth titanates, specifically Re 2 TiO 5 (Re La, Nd, Sm), with a particular emphasis on their microwave dielectric properties. The factors influencing the synthesis of La 2 TiO 5 compound through the traditional solid-state method were thoroughly investigated, with a significant finding being the notable impact of moisture absorption in La 2 O 3. The impact of variations in rare-earth cation radii on the structure and dielectric properties was systematically analyzed. Re 2 TiO 5 (Re La, Nd, Sm) ceramics crystallized into an orthorhombic structure with space group Pnam, which was confirmed through Rietveld refinement. The resulting materials demonstrated exceptional microwave dielectric properties characterized by a low permittivity range of 13.72–17.39, high-quality factors ranging from 8331 to 17,795 GHz, and a significantly reduced temperature coefficient of resonance frequency (−33.2∼-12.6 ppm/°C). The correlation between microwave dielectric properties and structural characteristics (including ionic polarizability, packing fraction, and bond valence) was investigated. The exceptional potential of these rare-earth titanates lies in their ability to meet the stringent requirements for low signal transmission delay in wireless communication systems, owing to their advantageous low permittivity within the microwave frequency spectrum. [ABSTRACT FROM AUTHOR]

Although a large electric-induced strain has been obtained in sodium bismuth titanate (Bi0.5Na0.5TiO3, BNT)-based ceramics using chemical modifications, the effect of initial BNT-based ceramic's polarity on modulating strain properties was rarely reported. Herein, we comparatively studied the effect of tantalum (Ta) doping on two BNT-based ceramics with different ferroelectric polarities, namely, (Bi0.5Na0.5)0.935Ba0.065TiO3–0.7%Bi2FeCrO6 and (Bi0.98Gd0.02)0.5Na0.5TiO3. The former locates at the morphotropic phase boundary (MPB), whereas the latter is close to pristine BNT ceramics. An effective critical point, located at the crossover between ferroelectric and relaxor, is constructed in the former ceramic and significantly enhances strain properties, whereas a useless one is found in the latter ceramic due to the retention of a non-ergodic relaxor and has merely limited ability to promote strain properties. Our results demonstrate that the ferroelectric polarity of the initial BNT-based ceramic matrix also plays an important role in pursuing high strain properties. [ABSTRACT FROM AUTHOR]

High- Q and temperature-stable ceramics are indispensable in microwave engineering. However, medium-permittivity (ε r ∼ 60, named as K60) microwave dielectric ceramics that meet the above demands are yet to be synthesized. High- Q Ba 4 Sm 9.33 Ti 16.5 Al 2 O 54 (BSTA) and Ca 0.6 Sm 0.27 Ti 0.8 Al 0.27 O 3 (CSTA) ceramics have large resonant frequency temperature coefficients (τ f) with opposite signs. The composites of the two are expected to have good dielectric properties, but there will be obvious diffusion when they are compounded with each other by sintering after directly mixing the raw powder, which would lead to severe deterioration in dielectric properties. In this work, the undesired diffusion can be effectively avoided by stacking two or three ceramic layers together, which are achieved by two methods named adhesive bonding and spark-plasma-sintering (SPS) cofiring. The finite element method (FEM) analysis with COMSOL Multiphysics proposed in this work can precisely predict the microwave dielectric properties of layered ceramics, helping to determine the ratio of different layers to reach near-zero τ f. The adhesive-bonded layered ceramics exhibit excellent dielectric properties: ε r = 62.2, Q × f = 21,400 GHz, and τ f = –0.7 ppm/°C. The SPS-cofired layered ceramics can be fabricated in one time, partially solving the problem of sintering mismatch between different layers, together with superior properties of ε r = 59.8, Q × f = 19,780 GHz, and τ f = –0.6 ppm/°C. These layered ceramics could fill the gap of high- Q and temperature-stable K60 microwave dielectric ceramics. The layer-stacking process and related FEM simulations can be used to design more high- Q and temperature-stable microwave dielectric ceramics and devices. • High- Q , temperature stable K60 ceramics are obtained (Q × f ∼ 20,000 GHz). • The diffraction in the directly-mixing process is thoroughly examined. • FEM simulation can precisely predict the properties of layered ceramics. • SPS-cofiring can partially solve the problem of sintering mismatch. [ABSTRACT FROM AUTHOR]

Gd ion-substituted barium bismuth titanate (BaBi4Ti4O15; BBTO) Aurivillius ceramics were synthesized to understand the preliminary impact through the structural, optical, frequency-dependent dielectric, conductivity, and complex modulus spectroscopic studies. X-ray diffraction (XRD) study confirmed the phase purity and crystallinity of the orthorhombic crystal system with A21am space group. The room temperature Raman study was correlated with the XRD results revealing a more feasible Aurivillius phase. A shift in the Curie temperature (Tm) towards low-temperature regions with increasing concentrations of Gd dopant was observed in temperature-dependent conductivity studies. The frequency-dependent conductivity study revealed a diffuse relaxor signature that degraded with dopant concentration explained by the modified Curie–Weiss law and normalized dielectric permittivity study. The frequency and temperature dependent modulus spectroscopic study indicated a dielectric relaxation mechanism in the presence of doubly ionized oxygen vacancies in pristine BBTO ceramics whereas the dominance of singly ionized oxygen vacancies was observed in Gd-doped one. The dielectric relaxation mechanism for pristine and doped Aurivillius are explained due to the thermal motion of the localized hopping process of electrons in variable oxidation states of different single ionized ions that depart from ideal Debye behavior. A detailed ac-conductivity study revealed the jumping relaxation mechanism or correlated barrier hopping mechanism (CBM) because of the localization of charge carriers, or the formation of polarons, respectively. [ABSTRACT FROM AUTHOR]

Sb-modified lithium bismuth titanate Li0.5Bi0.3Sb0.2TiO3 is prepared following the mixed oxide method. The development of a new compound with a single-phase orthorhombic crystal structure is approved from the XRD analysis at environmental temperature. The electrical behavior like dielectric and electrical conductivity are analyzed in a wide temperature as well as frequency range by the impedance analyzer, which exhibits that these properties effectively depend on frequency and temperature. The ac conductivity versus temperatures plots obeys the Arrhenius relation and confirm the presence of the mixed type of conductivity process like space charge conductivity created from oxygen ion vacancies, ionic-polaronic conductivity, and so on, in the sample. Ac conductivity versus frequency spectra is as per Jonscher's Universal Power law. [ABSTRACT FROM AUTHOR]

Sb-modified alkali bismuth titanate Li0.5Bi0.5−xSbxTiO3 (x = 0 and 0.1) compounds are prepared using the method of solid-state-reaction route. The XRD exploration in environmental conditions confirms the development of new compounds having single-phase orthorhombic crystal structures. Non-uniformly distributed grains are noticed in SEM micrographs for both compounds. The electric & dielectric behavior is analyzed by use of an impedance analyzer. The exploration of the dielectric behaviors of both compounds in a wide frequency range (100 Hz–1 MHz) & temperature range (30–500 °C) suggests that these characteristics are strongly dependent on frequency & temperature. Activation energy assessed from temperature variation of ac-conductivity in various zones recommends that the electric transport phenomenon obeys the Arrhenius equation and shows a mixed type of conductivity. [ABSTRACT FROM AUTHOR]

In this paper, detailed studies of effect of small amount of manganese substitution (at the zirconium site) on the structural, micro-structural, and electrical characteristics of lead zirconate titanate of Pb(Zr0.35–xMnxTi0.65)O3;x = 0, 0.02, 0.06, 0.10 (PZMT)) have been reported. The materials were prepared by using standard ceramic technology. The formation of the compounds and their basic crystal data have been studied through X-ray diffraction (XRD) method. The crystallite size and lattice strain of the compounds, evaluated from Scherrer's and Hall Williamson (H-W) equations, is found to be in the range of 40–50 nm and 11 × 10−4 to 50 × 10−4, respectively. Microstructures of different magnifications, revealing the surface nature of the compounds, have been recorded by field emission scanning electron microscope (FESEM). Effect of Mn+4 ions on electrical behavior (electrical impedance (Z*), electrical modulus (M*), conduction and relaxation phenomenon) of PZMT systems, over wide range of temperature and frequency, has been studied. [ABSTRACT FROM AUTHOR]

This paper considers the effect of adding niobium oxide (Nb2O5) to ferroelectric ceramics based on calcium titanate (CaTiO3), and establishes a connection between the observed alterations in strength and dielectric properties and the variation in the Nb2O5 dopant concentration in the ceramics' composition. The method of mechanochemical solid-phase synthesis was used as the main method for obtaining the ceramics, followed by thermal sintering under specified conditions in order to form a stable phase composition of the ceramics, and to initialize phase transformations in the composition. Based on the assessment of the phase composition of the resulting ceramics, it was determined that a growth in the Nb2O5 dopant concentration beyond 0.10 mol results in the formation of an orthorhombic-phase CaNb2O4 of the Pbcm(57) spatial system, the weight contribution of which grows. A growth in the Nb2O5 additive concentration results in the formation of two-phase ceramics, the formation of which allows for an enhancement in the mechanical strength of ceramics and resistance to external influences. During the study of the dependence of the strength properties on the dopant concentration alteration, a three-stage change in hardness and crack resistance was established, regarding both structural ordering and phase transformations. The measurement of dielectric characteristics showed the direct dependence of dielectric losses and the dielectric constant on the phase composition of ceramics. [ABSTRACT FROM AUTHOR]

A novel solid-phase synthetic approach was developed to produce a mineral-like composite ceramic based on strontium titanate (SrTiO3) and yttrium titanate (Y2Ti2O7) matrices for immobilizing radionuclides such as 90Sr and its daughter product 90Y, as well as lanthanides and actinides, via reactive spark plasma sintering technology (SPS-RS). Using XRD, SEM, and EDS analyses, the sintering kinetics of the initial mixed oxide reactants of composition YxSr1–1.5xTiO3 (x = 0.2, 0.4, 0.6 and 1) and structure-phase changes in the ceramics under SPS-RS conditions were investigated as a function of Y3+ content. In addition, a detailed study of phase transformation kinetics over time as a function of the heating temperature of the initial components (SrCO3, TiO2, and Y2O3) was conducted via in situ synchrotron XRD heating experiments. The composite ceramic achieved relatively high physicomechanical properties, including relative density between 4.92–4.64 g/cm3, Vickers microhardness of 500–800 HV, and compressive strength ranging from 95.5–272.4 MPa. An evaluation of hydrolytic stability and leaching rates of Sr2+ and Y3+ from the matrices was performed, demonstrating rates did not exceed 10−5–10−6 g·cm−2·day−1 in compliance with GOST R 50926-96 and ANSI/ANS 16.1 standards. The leaching mechanism of these components was studied, including the calculation of solution penetration depth in the ceramic bulk and ion diffusion coefficients in the solution. These findings show great promise for radioactive waste conditioning technologies and the manufacturing of radioisotope products. [ABSTRACT FROM AUTHOR]

Lead-free ceramics based on bismuth sodium lanthanum titanate (Bi0.4871Na0.4871La0.0172TiO3: BNLT) and barium titanate (BaTiO3: BT) were prepared by a modified two-step mixed-oxide method. Effects of BT content on the phase transition, thermal expansion behavior, mechanical and electrical properties of lead-free BNLT-BT ceramics were studied. The Burn's temperature and local polarizations were estimated from the thermal expansion data. Various aspects of understanding the polarization behavior and other effects in this system have also been investigated and discussed. The 0.96BNLT-0.04BT ceramics have shown the d33 value of 135 pC/N. The coercive field (Ec) and remanent polarization (Pr) were found to be 24 kV/cm and 9.0 µC/cm2, respectively. This may be useful in the future development of multifunctional lead-free materials in electronic applications. [ABSTRACT FROM AUTHOR]

(1- x)[0.82Bi 0.5 Na 0.5 TiO 3 -0.18Bi 0.5 K 0.5 TiO 3 ]- x AgNbO 3 ceramics (abbreviated as BNKT-100 x AN , x = 0–0.06) are fabricated by the solid state reaction method. It is discovered that silver niobate is completely dissolved into the lattice of 0.82Bi 0.5 Na 0.5 TiO 3 -0.18Bi 0.5 K 0.5 TiO 3 ceramics based on characterization. The relaxation mechanism and characteristics of BNKT-100 x AN ceramics are analyzed by dielectric temperature spectra and AC impedance spectra. The content of ordered domains and PNRs of BNKT-4AN ceramics is optimum, which enables it possess excellent electrostrain of 0.51%. The electrostrain almost remain constant after the 104 cycles test, suggesting that it also has great fatigue resistance. After polarization at high temperature, large electrostrain of 1.4% and inverse piezoelectric constants of 2004 pm/V are obtained at 150 °C in BNKT-4AN ceramics. The ultrahigh electrostrain is mainly promoted by the larger polarizability of the <111>-oriented and <001>-oriented defect dipoles, the same direction of defect dipoles and the spontaneous polarization direction of phase, the pinning effects of the defect dipoles on the PNRs and the collinear arrangement of the PNRs. This work indicates that lead-free piezoelectric ceramics is hopeful to be applied in piezoelectrics working at high temperature. Simultaneously, a new design paradigm also is provided for the preparation of piezoelectric ceramics with excellent performance. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate (PZT) ceramics possess great potential for practical applications and thus improving their piezoelectric properties is crucial. Pb 0. 9 9 − x Sm 0. 0 1 Ba x Zr 0. 5 3 Ti 0. 4 7 O3 (PSBZT) ceramics with high Curie temperature and excellent piezoelectric properties were fabricated via a conventional solid-state method, and the effect of Ba 2 + doping on the structural, dielectric, piezoelectric and ferroelectric properties was studied in detail. It is shown that doping of Ba 2 + significantly enhanced the piezoelectric properties of PSZT, the maximum d 3 3 ∼ 533 pC/N and T c ∼ 361 ∘ C at x = 0.02 were acquired. Furthermore, PSZT and PSBZT ceramics were used to prepare single element ultrasonic transducers, and their performance were compared and evaluated. The results demonstrate that the PSBZT ceramic-based transducer possesses better sensitivity and bandwidth than the PSZT ceramic-based transducer. [ABSTRACT FROM AUTHOR]

Using Al2O3 and TiO2 as raw materials, adding MgO as heat stabilizer and mullite as enhancer, aluminum titanate‐mullite multiphase ceramics were successfully prepared by solid phase synthesis. The effects of MgO and mullite were systematically studied on the phase composition, microstructure, thermal stability, sintering properties, and mechanical properties of aluminum titanate ceramics. The results showed that the introduction of Mg2+ can partially replace Al3+ to form MgxAl2(1‐x)Ti(1+x)O5 solid solution, improved the thermal stability of aluminum titanate ceramics, and promoted the formation and growth of grains, which reduced the sintering temperature. The crack deflections caused by mullite particles improved the mechanical properties. The filling effect of mullite particles and the formation of silica in mullite raw materials were conducive to ceramic densification. The statistics of Mg4M10 sample were as follows: the porosity was only 2.9%, the flexural strength was as high as 64.15 MPa, and the thermal expansion coefficient was 1.35 × 10−6 K−1 (RT‐700°C), encouraging the application of ceramics with high thermal mechanical properties. [ABSTRACT FROM AUTHOR]

Oxygen-deficient perovskites (PbTi1−xFexLiyO3−δ, x = 0–0.25, y = 0.15) were prepared by gel combustion technique. This study presents the effect of Fe3+ and Li+ on the morpho-structural and electrical properties of ceramics. Two structural behaviors have been identified, depending on the Fe3+ amount. At low Fe3+ concentrations (3.7%), the variation of the cell parameters is given by the tetragonal change toward cubic phase while at higher levels (>15%) the variation of the cell parameters comes mainly from Fe3+/Ti4+ ionic radii differences. Fe3+ doping at Ti sites creates oxygen and titan vacancies in order to compensate the Ti4+ charge. Introduction of oxygen vacancies reduces progressively band gap energy from 3.28 to 2.63 eV. ICP-OES measurements show that Pb and Ti are lower than theoretical formula which it generates supplementary contributions to the oxygen deficiency. Addition of Fe3+ and Li+ leads to an increase of lattice micro-strains from 17.07·10−4 up to 24.44·10−4, improving ionic conduction. Moreover, DFT calculation shows that the lattice distortion tends to decrease with the increase of the Fe concentration, in agreement with the XRD. Based on BET analysis, the pore diameter decreases from 56.9 to 16.6 nm with the increase of iron amount and is correlated with the relative densities that increase from 82.0 to 91.27%. According to EIS investigations, activation energy varies between 0.632 and 0.950 eV, showing that the conduction in perovskite ceramics is based on double ionized oxygen vacancies. The highest conductivity at 500 °C was obtained for samples doped with 15% Fe and 25% Fe (2.4 × 10−3 S·cm−1), sintered at 750 °C. [ABSTRACT FROM AUTHOR]

In this paper, zirconium-doped CaCu 3 Ti 4-x Zr x O 12 (0 ≤ x ≤ 0.3, CCTZO) ceramics were prepared by traditional solid-state reaction. The prepared CaCu 3 Ti 4-x Zr x O 12 display cubic phase structure, as shown by the XRD analysis, and interplanar spacing increase, as obtained by TEM. The surface morphologies, electrical conductivity, optical properties, solar and microwave thermal conversion characteristics of the synthesized samples were investigated in detail. The experimental results indicate that both the solar absorbance and thermal emittance of the samples could be tailored by Zr ions doping. In general, the CaCu 3 Ti 4-x Zr x O 12 system displays relatively high thermal radiation properties, with an optimal composition of CaCu 3 Ti 3.9 Zr 0.1 O 12 exhibiting a solar absorbance of 0.85 and a thermal emittance of 0.75. The incorporated Zr ions enhanced the solar–thermal conversion while weakened the microwave–thermal conversion. Under simulated solar irradiation (3 W/cm2), the equilibrium temperature of CaCu 3 Ti 3.9 Zr 0.1 O 12 could reach above 260 °C. The equilibrium temperature of CaCu 3 Ti 4 O 12 could reach up to 493 °C at a frequency of 2.45 GHz over 140 s. The results demonstrate that the CCTZO ceramics have the potential to emerge as the broadband electromagnetic wave–thermal conversion materials. [ABSTRACT FROM AUTHOR]

Nickel-zinc ferrite (NZF) discs and magnesium calcium titanite (MCT) dielectric ceramic discs were laminated and co-fired to prepare NZF/MCT bi-layer laminated heterostructure samples. The sintering shrinkage of NZF and MCT was matched well via adjusting the sintering temperature. Ion diffusion curves at the co-fired joint interface were derived by electron-probe microanalysis (EPMA) and fitted basing on infinite diffusion coupling model. Ion diffusion mechanism at the co-fired joint interface was investigated in detail. The results show that Zn2+ ions have the highest diffusion coefficient because of the smaller ion radius which is benefit for interstitial diffusion, while Ca2+ ions have the lowest diffusion coefficient and segregate along the interface of MCT side. Fe3+ ions have the biggest diffusion width because of the interstitial diffusion in the incompletely densified MCT. Sintered at 1260 °C, the maximum interdiffusion width is narrow to be about 102 μm. With increasing temperature, ion diffusion coefficient and diffusion distance both go up obviously. • Nickel-zinc ferrite (NZF) discs and magnesium calcium titanate (MCT) dielectric ceramic discs were co-fired to prepare heterostructure samples. • The microscopic morphology and EDS mappings near the interface of NZF/MCT were observed and identified, respectively. • Cations concentration curves were derived by EPMA and fitted. The diffusion width and diffusion coefficient were determined. • The ion diffusion mechanisms at co-fired joint interface were investigated in detail. [ABSTRACT FROM AUTHOR]

Bismuth sodium titanate (BNT)-based, lead-free piezoelectric materials have been extensively studied due to their excellent strain characteristics and environmental friendliness. In BNTs, the large strain (S) usually requires a relatively large electric field (E) excitation, resulting in a low inverse piezoelectric coefficient d33* (S/E). Moreover, the hysteresis and fatigue of strain in these materials have also been bottlenecks impeding the applications. The current common regulation method is chemical modification, which mainly focuses on forming a solid solution near the morphotropic phase boundary (MPB) by adjusting the phase transition temperature of the materials, such as BNT-BaTiO3, BNT-Bi0.5K0.5TiO3, etc., to obtain a large strain. Additionally, the strain regulation based on the defects introduced by the acceptor, donor, or equivalent dopant or the nonstoichiometry has proven effective, but its underlying mechanism is still ambiguous. In this paper, we review the generation of strain and then discuss it from the domain, volume, and boundary effect perspectives to understand the defect dipole behavior. The asymmetric effect caused by the coupling between defect dipole polarization and ferroelectric spontaneous polarization is expounded. Moreover, the defect effect on the conductive and fatigue properties of BNT-based solid solutions is described, which will affect the strain characteristics. The optimization approach is appropriately evaluated while there are still challenges in the full understanding of the defect dipoles and their strain output, in which further efforts are needed to achieve new breakthroughs in atomic-level insight. [ABSTRACT FROM AUTHOR]

We probed the structural modifications and electronic behavior of composites obtained from the admixture of a biphasic titanate ceramic system (Na2Ti3O7/Na2Ti6O13) with a poly(o-methoxyaniline, POMA) matrix. The composites were obtained by the addition of Na2Ti3O7/Na2Ti6O13to a POMA matrix in mass concentrations from 0 to 35%. The sodium titanates were synthesized by means of sonochemistry, while the polymer was obtained by conventional chemical polymerization. The structural analysis carried by XRD, FTIR and UV-Vis indicated mostly the presence of POMA, though the titanates could be identified in the composites with higher concentration. The XRD diffractograms showed narrow reflections that could be correlated to the Na2Ti6O13 phase and hydrogen titanates, whose presence indicates a process of partial substitution of H+ for Na+ ions. While the thermal degradation of the polymeric chains starts near 150 °C, the thermogravimetric and differential thermogravimetric (TG/dTG) analysis revealed that the presence of sodium titanates enhances the thermal stability of the composites. Finally, the addition of the biphasic ceramic to the composite increases the electrical resistivity drastically, from ≈ 102 Ω cm in the pure POMA to ≈ 104 Ω cm in the 35% composite. [ABSTRACT FROM AUTHOR]

We probed the structural modifications and electronic behavior of composites obtained from the admixture of a biphasic titanate ceramic system (Na2Ti3O7/Na2Ti6O13) with a poly(o-methoxyaniline, POMA) matrix. The composites were obtained by the addition of Na2Ti3O7/Na2Ti6O13to a POMA matrix in mass concentrations from 0 to 35%. The sodium titanates were synthesized by means of sonochemistry, while the polymer was obtained by conventional chemical polymerization. The structural analysis carried by XRD, FTIR and UV-Vis indicated mostly the presence of POMA, though the titanates could be identified in the composites with higher concentration. The XRD diffractograms showed narrow reflections that could be correlated to the Na2Ti6O13 phase and hydrogen titanates, whose presence indicates a process of partial substitution of H+ for Na+ ions. While the thermal degradation of the polymeric chains starts near 150 °C, the thermogravimetric and differential thermogravimetric (TG/dTG) analysis revealed that the presence of sodium titanates enhances the thermal stability of the composites. Finally, the addition of the biphasic ceramic to the composite increases the electrical resistivity drastically, from ≈ 102 Ω cm in the pure POMA to ≈ 104 Ω cm in the 35% composite. [ABSTRACT FROM AUTHOR]

The influence of donor (L a 3 +) and acceptor (S c 3 +) dopant on structural and electrical properties of lead-free B i 0.5 N a 0.5 Ti O 3 (BNT) ceramics system was investigated. Both donor and acceptor substitutions induced a structural transformation of pure BNT ceramics from a rhombohedral to a pseudocubic structure. Splitting of the (111) p c peak in pure BNT was considered symmetry identification for a rhombohedral structure. A micrometer level grain size (1.70 μm–2.81 μm), dense microstructure with good ferroelectric and piezoelectric performance (d 33 = 56 − 45 pC / N) was obtained. The 3% La content BNT ceramic shows an improved dielectric property. The Curie temperature increases from 355 °C for pure BNT to 365 °C for donor-doped and 370 °C for acceptor-doped BNT. The donor doping created cationic vacancies; acceptor doping induces oxygen vacancies that stabilized the polarization level. Maximum remnant polarization (P r) value has been obtained for 3% La-doped (P r = 27 μ C / c m 2) and 5% Sc-doped (P r = 20 μ C / c m 2) BNT system. Bipolar strain increased with the increase in donor dopant concentration resulting in a large electrostrictive coefficient (Q11 ∼ 0.0122%–0.045%) has been obtained. Electric field-induced unipolar strain value was enhanced to its maximum value (Smax = 0.14%) for 3% La content with normalized strain d 33 ∗ = 209 pm / V and Smax = 0.13% for 5% Sc with normalized strain d 33 ∗ = 155 pm / V at an applied electric field of 70 kV/cm and 50 kV/cm, respectively. The enhanced strain was considered to be associated with low internal bias field and maximum polarization level. In terms of capacitive response, 5% Sc holds a maximum current (∼0.017 mA) during polarization switching. [ABSTRACT FROM AUTHOR]

All-solid-state supercapacitors (ASSS) are considered promising candidates to eliminate the safety issues of liquid-electrolyte-involved devices, while lithium lanthanum titanate perovskite compounds have been reported as suitable electrolytes due to their high chemical stability. However, the unsatisfactory ionic conductivity compared with liquid-electrolytes still hinders their applications in emerging requirements. Aiming to find the factors impacting the intrinsic capacitances of the lithium lanthanum titanate perovskite compounds when used in ASSS, a series of Li0.33La0.56□0.11Ti1-xSnxO3 (LLTS, □ represents vacancy) compounds with different Sn4+ concentrations (nominal x = 0–5 mol%) have been synthesized in this study. The as-prepared LLTS ceramic with the Sn4+ content of 0.1 mol% exhibited the highest ionic conductivity, while more Sn4+ reduced the ionic conductivity in the bulk pellets. The ionic conducting ability of the electrolyte determines the overall electrical performance of the assembled ASSBs, i.e., the better ionic conductivity of the LLTS leads to the higher capacitance of the devices. In addition, we have found the coexistence of electrical double-layer capacitance and dielectric polarization capacitance in the LLTS-based ASSS, which could provide the guidance in designing high-performance devices with similar configurations. [ABSTRACT FROM AUTHOR]

Bi0.5Na0.5TiO3 (abbreviated as BNT)-based ceramics are considered the promising candidates for lead-free piezoelectric materials to replace the widely used lead zirconate titanate (PZT)-based piezoelectric ceramics. Piezoelectric properties could be modulated by porous structures to meet the needs of piezoelectric energy converters. Porous (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNT-6BT) ceramics had been prepared by using kiwi pollen as a sacrificial template for inducing U-shaped micropores. Porosity correlations of dielectric and piezoelectric properties of the porous BNT-6BT ceramics in the relative porosity range of 0–50% were obtained and analyzed. The temperature stability of the dielectric constant of porous ceramics is significantly improved, while the dielectric constant of porous ceramics decreases rapidly with the increase of the amount of pollen added, and then remains stable. The longitudinal piezoelectric coefficient d33 and the transverse piezoelectric coefficient d31 of porous ceramics decrease slowly with porosity. It was found that the ceramic barrier hinders the pinning effect of the micro stress and strain on domain walls, which makes the piezoelectric properties of porous ceramics well maintained. Porous BNT-based ceramics have great application value in underwater acoustic transducers and other fields. [ABSTRACT FROM AUTHOR]

In this study, the temperature sensing behaviors of emissions of Stark sublevels in Er3+/Yb3+ codoped lead lanthanum zirconate titanate (PLZT) transparent ceramic were examined. Based on the temperature-dependent upconversion fluorescence spectra excited by 980 nm, the emission intensities of the Stark sublevels 2H11/2(1, 2), 4S3/2(1, 2), and 4F9/2(1, 2, 3) were obtained upon increasing the temperature from 160 to 320 K. All the transitions present strong temperature dependence under the competitive effects of thermal excitation and nonradiative relaxation. The optical temperature sensing properties of 2H11/2/4S3/2(1), 2H11/2/4S3/2(2), 2H11/2/4F9/2(1), 2H11/2/4F9/2(2), and 2H11/2/4F9/2(3) were investigated using the fluorescence intensity ratio (FIR) technique. The largest absolute sensitivity Sa of 142.4 × 10–4 K−1 was obtained based on the FIRs of 2H11/2/4F9/2(1) at 320 K, which is approximately 26 times larger than that of traditionally used thermal coupled levels 2H11/2/4S3/2 in the considered sample. In contrast, the maximum relative sensitivity Sr was 2.21% K−1 at 203 K. A comparison of these results with those of other Er3+/Yb3+ codoped materials reveals that Er3+/Yb3+: PLZT ceramics are a promising thermometer material at low temperatures. Applying FIRs based on the photoluminescence of Stark sublevels is a practical approach to achieving greater thermometric efficiency. [ABSTRACT FROM AUTHOR]

Influence of (K0.5Bi0.5)TiO3 (KBT) dopants on crystal and microstructure, ferroelectric and dielectric properties of ceramic composition from morphotropic phase boundary in the system (1–x–y)(Na0.5Bi0.5)TiO3 – xBaTiO3 – y(K0.5Bi0.5)TiO3 (x = 0.06, y = 0–0.15) additionally modified by ZnO additives was studied using a complex of methods. Changes from 42.8 nm to 62.6 nm of the volume-weighted crystallite size distribution function G(L) corresponding to coherent scattering regions were observed. The microstructure and the second harmonic generation data indicated a change in the relative content of polar nanoregions in tetragonal nonpolar matrix. Decrease in temperatures of phase transitions Tm and Td was observed with KBT concentration increasing. [ABSTRACT FROM AUTHOR]

Achieving excellent pyroelectric performance remains a challenge for lead‐free piezoelectric ceramics. To meet the requirements of both an enhanced pyroelectric coefficient at room temperature and good thermal stability during the encapsulation of pyroelectric devices, (1–x)K0.48Na0.52NbO3–xBi0.5Ag0.5ZrO3–0.2%Fe2O3 (KNN–BAZ–Fe) lead‐free ferroelectric ceramics with high Curie temperatures were prepared to obtain improved pyroelectric performance via the coexistence of multiple symmetries. The variation of BAZ content led to the formation of rhombohedral–orthorhombic–tetragonal phase boundary and promoted grain growth, resulting in the best pyroelectric coefficient (p = 5.09 × 10−4 C m−2°C−1) and enhanced figures of merit (Fi = 0.2084 × 10−9 (m V−1), Fv = 0.0142 m2 C−1, Fd = 0.0947 × 10−4 Pa−1/2, and Fe = 17.66 J m−3 K−2) for infrared (IR) detection when x = 0.05. The room‐temperature pyroelectric coefficient obtained in this study is approximately four times that of the pure KNN ceramic and is the maximum value reported for niobate‐based piezoelectric ceramics. Moreover, compared with the poor thermal stability of barium titanate‐ and bismuth sodium titanate‐based ceramics because of their ultralow Curie temperature or thermal depolarization temperature, the ceramics investigated here exhibit much better thermal stability because of their high Curie temperature (TC > 300°C) and diffused phase‐transition behavior, making them more adaptable for practical applications. These results suggest that KNN–xBAZ–Fe ceramics are attractive candidates for applications in the field of IR sensors. [ABSTRACT FROM AUTHOR]

With the ever-increasing demand for energy, research on energy storage materials is imperative. Thereinto, dielectric materials are regarded as one of the potential candidates for application in advanced pulsed capacitors by reason of their ultrahigh energy-storage density, low energy loss, and good thermal stability. Among the numerous dielectric materials for energy storage, sodium bismuth titanate (Bi0.5Na0.5TiO3, BNT) with high saturation polarization, as one of the successful alternatives to lead-based materials, has been extensively studied. However, degraded dielectric and ferroelectric properties as a consequence of chemical alterations usually produced by inhomogeneity in microstructure and composition due to the ion volatilization during preparing, thus affecting performance of devices. Hence, this review served to encompass the current state and progress on the optimization of energy storage performance in lead-free BNT-based materials over the past few years, including ceramics, multilayer ceramics, thin films, and thick films, involved in solid solution modification, metal/metallic oxide doping, process optimization and other related aspects to optimize energy storage performance. Furthermore, some prospective approach in the improvement of energy storage performance for BNT-based materials were also provided in this work according to the existing theoretical and experimental results, to impel their practical application. [ABSTRACT FROM AUTHOR]

The demand for high-temperature endurable dielectric materials with higher thermal stability in electronic systems operating under extreme temperatures sets a significant channel for the electronic industry. This work focuses on the dielectric and impedance behavior for lead-free Ba 1− x Nd 2 x ∕3 Zr 0.1 Ti 0.9 O 3 (BNZT); (0.00 ≤ x ≤ 0.04) between 300 ∘C – 400 ∘C and synthesized by conventional solid-state reaction method at optimum temperatures. Structural characterizations confirmed the tetragonal (P 4 mm symmetry) structure formations for the BNZT ceramics. XPS analysis confirmed the Nd-substitution at the Ba-site in the BNZT ceramics. FE-SEM study showed grain growth reduction with enhanced grain boundaries. The dielectric study showed lower dielectric loss with enhanced dielectric permittivity at high temperatures. Impedance analysis confirmed the negative temperature coefficient of resistance (NTCR) and non-Debye type behavior with higher thermal stability. Singly-ionized oxygen vacancies mainly govern the conduction process in BNZT ceramics. Enhanced dielectric and impedance properties suggest that Nd-substituted BNZT electroceramics are promising materials for applications in high-temperature-based energy storage systems. • Ba 1−x Nd 2 x ∕3 Zr 0.1 Ti 0.9 O 3 (BNZT; 0.00≤ x ≤0.04) electro-ceramics have been successfully synthesized using solid-state reaction method. • Structural analyses confirm the tetragonal phase (P4mm) formation with the Nd-substituted at the Ba-site in BNZT ceramics. • Enhanced dielectric permittivity with lower dielectric loss is observed in Nd-substituted BNZT ceramics. • Impedance study shows enhanced electrical properties with NTCR behavior and higher grain boundary effect in BNZT ceramics. • Conduction process is mainly governed by singly-ionized oxygen vacancies with the non-Debye type behavior in BNZT ceramics. [ABSTRACT FROM AUTHOR]

La‐ and Sn‐cosubstituted lead zirconate titanate (PbLaZrSnTiO3) ceramics are synthesized using a solid‐state reaction route. These PbLaZrSnTiO3(PLZST) ceramics in pure form are found to exist in dual phase (Cc+P4mm) and single phase (Cc) depending on the amount of La/Sn cosubstitution. PLZST ceramics exhibit thin P–E loops with enhanced polarization when measured at 393 K. Olsen cycle method is used to estimate the pyroenergy harvesting abilities of the samples under study. The estimated maximum energy storage density for PLZST (50/30/20) ceramics at 393 K is 1.16 J cm−3 [efficiency (η) > 96%]. The PLZST ceramics exhibit a remarkable hardness of 9.08 GPa. These results indicate that PLZST ceramics with excellent multifunctional properties are potential candidates in the field of electroceramic devices. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) is growing rapidly with strong demand from industrial automation, digital twins, and Internet of Things (IoT). In contrast to the manual installation of discrete devices, piezoelectric transducers by directly coating and patterning the piezoelectric materials on the engineering structures show the potential for achieving SHM function with improved benefits over cost. Until the recent years, high-performance lead-free piezoelectric ceramic coatings, including potassium–sodium niobate (KNN) and bismuth sodium titanate (BNT)-based coatings, are produced by thermal spray method. This article reviews the background and progresses of using thermal spray method for fabricating piezoelectric ceramic coatings and their values for SHM applications. The review shows the combination of environmentally friendly lead-free compositions, and the scalable thermal spray processing method opens substantial application opportunities. Ultrasonic SHM technology enabled by thermal-sprayed piezoelectric ceramic coatings is an important area where the lead-free piezoelectric ceramic materials can play with their technical competitiveness and commercial values over the lead-based compositions. [ABSTRACT FROM AUTHOR]

Cobalt-doped potassium hexa-titanate (Cox:K2Ti6O13 (x = 0.05, 0.10, 0.15 mole%)) ceramics were synthesized by the solid-state reaction method. The XRD patterns confirmed single-phase development in a monoclinic symmetry of various samples, and they were used for different structural calculations of Cox:K2Ti6O13 ceramics. The dielectric constant, tanδ, electrical modulus, and ac conductivity of Co-doped K2Ti6O13 were studied in the temperature range of 100–500 °C. Anomalies were observed in graphs of the dielectric constant versus temperature, showing the transition phase in the studied samples. Dielectric peaks at transition temperature decreased with an increasing frequency, and the peaks shifted toward higher temperatures, illustrating the relaxation of the dielectric materials. The composition with x = 0.10 showed low dielectric loss and a higher dielectric constant and can be utilized for high-temperature dielectric material. Small doping of cobalt improved the ac conductivity of K2Ti6O13 ceramics due to the increase in the spin–phonon interaction and dominant electron hopping conduction; however, the conductivity diminished with substantial doping because of the contraction of the tunnel space and ambushing of conduction electrons. The uniqueness of this study is in the high dielectric optimization of lead-free ceramic Cox:K2Ti6O13 and the discovery of positive temperature coefficients of the resistivity of these ceramic samples. [ABSTRACT FROM AUTHOR]

Dielectric permittivity was studied in ceramics of relaxor ferroelectric bismuth-sodium titanate Na0.5Bi0.5TiO3. The measurements were performed on as sintered and heat treated in vacuum samples. The diffuse dielectric anomalies associated with the structural phase transitions were observed in as sintered samples. The intense peak of permittivity (emax ~ 104) appeared after heat treating in vacuum. The anomaly of e(T) was contributed by slow polarization processes (f < 10 kHz) and was non-stable, vanishing on heating in air up to ~ 800 K. Temperature and frequency dependencies of e were described by using Cole-Cole model with accounting thermally stimulated decay of the non-stable polarization. It is supposed that the dielectric anomaly is determined by space charge polarization mechanism. Oxygen vacancies V••O and electrons localized on titanium ions Ti′ Ti are assumed to be responsible for the phenomenon observed. [ABSTRACT FROM AUTHOR]

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This work reports the synthesis and electrical characterization of Ba0.77Ca0.227Y0.003TiO3 (BCT:Y) and Ba0.77Ca0.227Eu0.003TiO3 (BCT:Eu) ceramics. The powders were synthesized by the polymeric precursor method and presented majority Ba0.77Ca0.23TiO3 (BCT) phase after calcination at 600 °C for 4 h. Afterwards, the ceramics were sintered at 1350 °C under reducing atmosphere. X-ray diffraction, scanning electronic microscopy and impedance spectroscopy techniques were used to study the structural, microstructural, and electrical characteristics, respectively. The sintered ceramics exhibit homogeneous microstructure with high relative density and majority BCT phase. The BCT:Y sample presented PTCR (Positive Temperature Coefficient of Resistivity) behavior with room temperature resistivity of 1.1⋅104 Ω⋅cm (grain) and 6.8⋅105 Ω⋅cm (grain boundary), and a PTCR jump of about three and two orders of magnitude, respectively, suggesting a core–shell structure at the grain boundary region. On the other hand, BCT:Eu showed normal dielectric behavior that was associated with the Eu reduction during the sintering process. [ABSTRACT FROM AUTHOR]

Practical pyroelectric materials require excellent pyroelectric performance, high depolarization temperature, and good temperature stability. In this work, the microstructure, ferroelectric, dielectric, and pyroelectric properties were studied systematically in (Bi0.5Na0.5)TiO3–0.1%MnCO3 (BNT–Mn) lead-free ceramics. It is observed that the pyroelectric coefficient p reaches 2.90 × 10−4 C m−2 K−1 at room temperature in the samples. Due to the low dielectric constant (291) and dielectric loss (0.010), the figures of merit (FoMs) Fi, Fv, and FD are as high as 1.03 × 10−10 m/V, 4.05 × 10−2 m2/C, and 1.86 × 10−5 Pa−1/2, measured at 1 kHz. With the increase in temperature, the p and FoMs change slightly, showing good temperature stability. More importantly, a relatively high depolarization temperature of 205 °C is achieved, which should help deliver reliable operation in practice. In general, all performances reveal that BNT–Mn ceramics are expected to pave the way for uncooled infrared detector applications. [ABSTRACT FROM AUTHOR]

Using the method of sintering by microwave heating at a rate of 10–100°C/min to a temperature of 1250 °C without isothermal hold, we obtain ceramic samples with the composition Ba0.75Sr0.25TiO3. The experiments are performed on a gyrotron complex for the high-temperature microwave treatment of materials, which is operated at a frequency of 24 GHz with a maximum power of 5 kW. The features of the formation of a solid solution in the sintered samples are analyzed. The dependence of the intensity of recrystallization growth of grains on the microwave-heating rate during the sintering is demonstrated. The permittivity of the samples obtained by microwave sintering with heating rates of 10 and 30 °C/min amount to 3600–4400 in the frequency range 25Hz–3MHz at room temperature. [ABSTRACT FROM AUTHOR]

TiO 2 -added Ba 4 (Sm 0.65 Nd 0.35) 9.33 Ti 17.75 Al 0.33 O 54 (BSNTA) ceramics were fabricated with a solid-state reaction method. Slight TiO 2 addition increased the dielectric constant (ε r) of BSNTA ceramics and brought about a near-zero temperature coefficient of resonant frequency (τ f). Sintering in oxygen increased the density of TiO 2 -added BSNTA ceramics and surprisingly concurrently improved the ε r and Q × f value. Thermally stimulated depolarization current (TSDC) measurements indicated that TiO 2 addition introduced oxygen vacancies (V O..) and Ti Ti ' − V O.. defect dipoles and that an oxygen-sufficient sintering atmosphere decreased the concentration of these defects and thus increased Q × f values. From the viewpoint of defect behaviors, this observation offered original insight into the mechanism by which the sintering atmosphere had impacts on the Q × f value of titanate ceramics. Satisfying dielectric properties (ε r = 79.5, Q × f = 14,840 GHz, τ f = 0 ppm/°C) were attained in oxygen-sintered BSNTA-0.6%TiO 2 ceramics that might be suitable for the manufacture of miniature microwave devices such as filters and antennas. [ABSTRACT FROM AUTHOR]

The effect of Nb/Ta donor doping on the piezoelectricity, thermal stability, and fatigue resistance of bismuth titanate Bi 4 Ti 3 O 12 (BIT) ceramics was investigated in relation to their structural and oxygen vacancy-related electrical properties. As the Nb/Ta doping amount increased, the activation energy of oxygen vacancy conduction increased, indicating a reduction in the concentration of oxygen vacancies. The improved electrical insulating properties of the Nb/Ta-doped Bi 4 Ti 3 O 12 ceramics (BTNT) with fewer oxygen vacancies, contributed to their effective poling and strong piezoelectricity. Outstanding piezoelectric performance with high piezoelectric constant (39 pC/N) and Curie temperature (690 °C) could be achieved in the 0.005 mol Nb/Ta-doped BTNT ceramic with high density and anisotropic grain growth. The BTNT ceramics exhibited superior thermal aging stability and fatigue resistance compared to the BIT ceramic, suggesting that the reduction of oxygen vacancy defects plays a decisive role in enhancing elevated-temperature-induced and electric-field-induced degradation stabilities. [ABSTRACT FROM AUTHOR]

Niobium (Nb)‐doped lead‐tin‐zirconate‐titanate (PSZT) ceramics near the lead‐zirconate‐titanate 95/5 orthorhombic AFE‐rhombohedral FE morphotropic phase boundary (PSZT 13.5/81/5.5 ‐1.6Nb) were prepared with up to 10 mol.% of hafnium (Hf) substituted for zirconium. The ceramics were prepared by a traditional solid‐state synthesis route and sintered to near full density at 1150°C for 6 h in sealed alumina crucibles with self‐same material as the lead vapor source. All compositions were ∼98% dense with no detectable secondary phases by X‐ray diffraction. The grain size was ∼3 μm for all compositions, consisting of equiaxed grains with intergranular porosity. The compositions exhibited remnant polarization values of ∼32 μC/cm2. Depolarization by the hydrostatic pressure‐induced FE‐AFE phase transition occurred at 310 MPa for all compositions, resulting in a total depolarization output of 32.4 μC/cm2 for the PSZT ceramics. Evaluation of the R3c‐R3m and R3m‐Pm 3¯$\overline 3 $ m phase transition temperatures by impedance spectroscopy showed temperatures on heating ranging from 86 to 92°C and 186 to 182°C, respectively, for increasing nominal Hf content. Thermal hysteresis of the phase transitions was also observed in the ceramics, with the transition temperature on cooling being 1–4°C lower. The study demonstrated that the PSZT ceramics are relatively insensitive to variations in Hf content in the range of 0 to 10 mol.%. [ABSTRACT FROM AUTHOR]

Influence of dopants on structure, microstructure, dielectric and ferroelectric properties of ferroelectric-relaxor (Na0.5Bi0.5)TiO3 ceramics modified by Ba2+ cations and overstoichiometric additives (SiO2 and Na2O) was studied. Changes in structure, microstructure, and dielectric parameters were observed depending on solid solutions compositions. [ABSTRACT FROM AUTHOR]

In this study, a series of novel negative temperature coefficient thermistor materials based on A 2 Ti 2 O 7 (A = Sm, Eu, Y) titanate ceramics have been developed for high-temperature applications. The A 2 Ti 2 O 7 (A = Sm, Eu, Y) ceramics showed cubic pyrochlore structures with dense morphology in X-ray diffraction and scanning electron microscopic analyses. These ceramics showed typical NTC characteristics in a wide temperature range of 673–1473 K, accompanied by resistance drift rates of 2.71%, 1.63%, and 4.95% for 400 h of ageing at 1173 K. The proposed ceramics have high resistivity and thermal constants B that ensure their better sensitivity at high temperatures and also show unique oxygen insensitivity. These properties outperform those of traditional high-temperature NTC materials composed of perovskite-type or scheelite-type ceramics, making A 2 Ti 2 O 7 (A = Sm, Eu, Y) ceramics promising candidates for fabricating high-temperature NTC thermistors. [ABSTRACT FROM AUTHOR]

Plenty of works have done to enhance the piezoelectricity of potassium-sodium niobate (KNN), aiming to replace lead-zirconate titanate (PZT) in the consideration of eco-friendly requirement. However so far, KNN ceramics with high piezoelectric performances tend to have a low mechanical quality factor (Q m), which could result in excessive dielectric loss, especially when working in high frequencies. Thus, increasing Q m is a crucial task in KNN-based ceramics. By constructing phase boundaries together with inducing oxygen vacancies, a new KNN ceramic system is built by using conventional solid-state method with high Q m (>250), high piezoelectric performance as well as outstanding temperature stability. Optimum overall properties of KNN-based ceramics can be as large as d 33 = 231 pC/N, Q m = 355, T C = 366 °C. This work provides a deeper insight to KNN-based ceramics with high mechanical quality factor and makes a progress on the high frequency application of lead-free ceramics. [ABSTRACT FROM AUTHOR]

The conditions for the preparation of the solid solutions of a binary system of barium-strontium titanates with the substitutions in the A -sublattice with the rare-earth elements (REE), including the solid-phase synthesis, mechanical activation and sintering of dispersed-crystalline products by the conventional ceramic technology, were optimized. The presence (absence) of the impurity phases was established depending on the size effect of the REE. The precision X-ray diffraction analysis revealed the features of the phase formation in the studied solid solutions and showed that the "behavior" of the structural characteristics of the solid solutions with the participation of the REE is determined by the limiting conditions of the isomorphism and anion excess of the media under study. An assumption is made about the nature of the formation of a fine-grained landscape of the modified solid solutions, associated with the multicluster structure of the crystallite structure and the formation of the ballast phases during their synthesis. The dependences of the dielectric properties of the solid-state solution on the external influences – temperature, frequency of an alternating electric field and strength of a constant field – have been established. The possibility of choosing on the basis of the obtained data, promising for practical applications of the compositions is shown. [ABSTRACT FROM AUTHOR]

This work compares the dielectric properties of two new materials. One was 0.88 bismuth manganite–0.12 lead titanate (noted BM–PT hereafter) ceramics composite obtained by standard high-temperature sintering. The second composite was obtained from powdered ceramics dispersed in epoxy glue (noted BM–PT–epoxy). The occurrence of four phases in the ceramics, using X-ray powder diffraction (XRD), was recognized: orthorhombic Pbam , cubic Pn 3 ‾ m , cubic Pm 3 ‾ m , and monoclinic P 2 /m phase. Pseudo-Voigt function fitting confirmed significant structural disorder in the BiMn 2 O 5 crystal lattice. Analysis of broadband dielectric spectroscopy data confirmed the applicability of the small polaron model to explain detected relaxation processes. Involvement of oxygen vacancies in relaxation and their correspondence to ordered, uniform potential wells in crystal lattices was deduced. Electric conductivity relaxation times behavior proved the sensitivity of the ceramics' electrical features to hydrostatic pressure. BM–PT–epoxy composite exhibited dielectric permittivity and losses two orders of magnitude lower than those of BM–PT ceramics that opened new prospects to application. One relaxation process in BM–PT–epoxy composite related to the ceramics fill contribution. Other induced relaxation, observed only in this composite, was attributed to interactions at interfaces between the introduced powdered ceramics and the epoxy glue matrix. We showed that stresses generated either by hydrostatic pressure or through the interfacial interaction of epoxy matrix led to the same results: relaxation times shortening. [ABSTRACT FROM AUTHOR]

To investigate the nonstoichiometric effect of (Bi 0.5 Na 0.5)TiO 3 (BNT) ceramics on their properties, we propose a novel chemical expression, (Bi 0.5+ x Na 0.5−3 x)TiO 3. The nonstoichiometric effect of BNT can be explored in compounds with this composition without being hampered by the charge imbalance problem. With x ranging from −0.02 to 0.02, we find that the morphological, dielectric, ferroelectric, and electrostrain properties differ considerably between Na-rich and Bi-rich ceramic samples. The average grain size (AGS) increased significantly in Na-rich samples compared to that in stoichiometric BNT, while it decreased slightly in Bi-rich samples. The dielectric characteristics measured from 30 °C to 500 °C indicate that conductivity is activated in Na-rich nonstoichiometric samples but is effectively suppressed in Bi-rich nonstoichiometric samples. The ferroelectric properties also show the same trend. In Na-rich samples, elliptical polarization against electric field (P - E) hysteresis loops were detected, indicating a conductive character induced by high electric field loading. However, saturated P - E loops are observed in Bi-rich samples with well-inhibited conductivity. Furthermore, compared to stoichiometric BNT and nonstoichiometric x = 0.02 Bi-rich samples, (Bi 0.5+ x Na 0.5−3 x)TiO 3 samples with x = 0.01 exhibit higher electrostrain from 30 °C to 150 °C. Based on the assumption of charge balance, our findings indicated that the presence of 1 mol% excess Bi would facilitate significant improvement in the dielectric, ferroelectric, and electrostrain properties of BNT and BNT-based systems. [ABSTRACT FROM AUTHOR]

Zinc-substituted magnesium titanate ZnxMg1−xTiO3 (x = 0.00–0.10, δx = 0.025) solid solutions were synthesized using auto-ignition combustion process and characterized for structural, dielectric and reflection properties. X-ray diffraction analysis discovered the creation of single-phase MgTiO3. Scanning electron microscopy (SEM) indicated the existence of low porosity closely packed grains. The study of the dielectric properties indicated that for ZnxMg1−xTiO3 with x = 0.05, a reasonably great combination of the relative permittivity (ɛr) with value 16.60, loss tangent (tanδ) of 0.9 × 10−3 and temperature coefficient of resonant frequency (τf) of − 41.37 ppm/°C at 10 kHz was observed. The electromagnetic reflection analysis at microwave frequencies (12.4–26.5 GHz) revealed that composition x = 0.05 shows maximum 90% reflection bandwidth of 5.60 GHz in the Ku frequency band and 4.59 GHz in the K frequency band. These materials with low to intermediate relative permittivity, low losses, and a minor negative temperature coefficient of resonant frequency might be utilized as a resonator, antenna, and filter substrate for next-generation communication devices. [ABSTRACT FROM AUTHOR]