High temperature dielectrics in the ceramic system K0.5Bi0.5TiO3-Ba(Zr0.2Ti0.8)O3-Bi(Zn2/3Nb1/3)O3

Ceramics in the system (1-x)[0.5K_0.5Bi_0.5TiO₃-0.5Ba(Zr_0.2Ti_0.8)O₃]-xBi(Zn_2/3Nb_1/3)O₃ have been fabricated by a solid-state processing route for compositions x≤0.3. The materials are relaxor dielectrics. The temperature of maximum relative permittivity, T_m, decreased from 150 °C for composition x=0, to 70 °C for x=0.2. The x=0.2 sample displayed a wide temperature range of stable relative permittivity, ε_r, such that ε_r=805±15% from −20 to 600 °C (1 kHz). Dielectric loss tangent was ≤0.02 from 50 °C to 450 °C (1 kHz), but due to the tanδ dispersion peak, the value increased to 0.09 as temperatures fell from 50 °C to −20 °C. Values of dc resistivity were of the order of ~10⁹ Ω m at 300 °C. These properties are promising in the context of developing new high temperature capacitor materials.     

Temperature-stable dielectric ceramics based on Na0.5Bi0.5TiO3

Multiple ion substitutions to Na_0.5Bi_0.5TiO₃ give rise to favourable dielectric properties over the technologically important temperature range ?55?°C to 300?°C. A relative permittivity, ε_r,?=?1300?±?15% was recorded, with low loss tangent, tanδ?≤?0.025, for temperatures from 310?°C to 0?°C, tanδ increasing to 0.05 at ?55?°C (1?kHz) in the targeted solid solution (1–x)[0.85Na_0.5Bi_0.5TiO₃–0.15Ba_0.8Ca_0.2Ti_1-yZr_yO₃]–xNaNbO₃: x?=?0.3, y?=?0.2. The ε_r-T plots for NaNbO₃ contents x?<?0.2 exhibited a frequency-dependent inflection below the temperature of a broad dielectric peak. Higher levels of niobate substitution resulted in a single peak with frequency dispersion, typical of a normal relaxor ferroelectric. Experimental trends in properties suggest that the dielectric inflection is the true relaxor dielectric peak and appears as an inflection due to overlap with an independent broad dielectric peak. Process-related cation and oxygen vacancies and their possible contributions to dielectric properties are discussed.     

Composition-dependent xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 bulk ceramics for high energy storage applications

This work reports the composition dependent microstructure, dielectric, ferroelectric and energy storage properties, and the phase transitions sequence of lead free xBa(Zr_0.2Ti_0.8)O₃-(1-x)(Ba_0.7Ca_0.3)TiO₃ [xBZT-(1-x)BCT] ceramics, with x?=?0.4, 0.5 and 0.6, prepared by solid state reaction method. The XRD and Raman scattering results confirm the coexistence of rhombohedral and tetragonal phases at room temperature (RT). The temperature dependence of Raman scattering spectra, dielectric permittivity and polarization points a first phase transition from ferroelectric rhombohedral phase to ferroelectric tetragonal phase at a temperature (T_R-T) of 40?°C and a second phase transition from ferroelectric tetragonal phase - paraelectric pseudocubic phase at a temperature (T_T-C) of 110?°C. The dielectric analysis suggests that the phase transition at T_T-C is of diffusive type and the BZT-BCT ceramics are a relaxor type ferroelectric materials. The composition induced variation in the temperature dependence of dielectric losses was correlated with full width half maxima (FWHM) of A₁, E(LO) Raman mode. The saturation polarization (P_s) ≈8.3?μC/cm² and coercive fields ≈2.9?kV/cm were found to be optimum at composition x?=?0.6 and is attributed to grain size effect. It is also shown that BZT-BCT ceramics exhibit a fatigue free response up to 10⁵ cycles. The effect of a.c. electric field amplitude and temperature on energy storage density and storage efficiency is also discussed. The presence of high T_T-C (110?°C), a high dielectric constant (ε_r ≈?12,285) with low dielectric loss (0.03), good polarization (P_s ≈?8.3?μC/cm²) and large recoverable energy density (W?=?121?mJ/cm³) with an energy storage efficiency (η) of 70% at an electric field of 25?kV/cm in 0.6BZT-0.4BCT ceramics make them suitable candidates for energy storage capacitor applications.     

Texture development and dielectric relaxor behavior of 0.80Na0.5Bi0.5TiO3–0.20K0.5Bi0.5TiO3 ceramics templated by plate-like NaNbO3 particles

Plate-like NaNbO₃ particles were used as templates to fabricate grain-oriented 0.96(0.8Na_0.5Bi_0.5TiO₃–0.2 K_0.5Bi_0.5TiO₃)–0.04NaNbO₃ (NKBT) ceramics. The effects of the sintering temperature and the soaking time on the grain orientation and the microstructure of the textured NKBT ceramics were investigated, and the dielectric relaxor behavior is discussed. The results show that textured ceramics were successfully obtained with orientation factor more than 0.8. The textured ceramics have a microstructure with strip-like grains aligning in the direction parallel to the casting plane. The degree of grain orientation increases initially, then decreases with increasing sintering temperature, and increases continuously with increasing soaking time. The textured NKBT ceramics shows obvious dielectric relaxor characteristics which can be well explained by microdomain–macrodomain transition theory with calculating criterion K. The results show that formation of texture is beneficial to microdomain–macrodomain transition, which lead to weaken relaxor behavior and raise the dielectric constant at T_tr.     

Sr和Mn复合掺杂(Na0.8K0.2)0.5Bi0.5TiO3无铅压电陶瓷

用固相法制备了(Na0.8K0.2)0.5Bi0.5TiO3+xmol%SrCO3+xmol%MnCO3(0≤x≤1.25%)(简称NKBTSM)无铅压电陶瓷,用XRD、SEM、Agilent 4294A精密阻抗仪等对该体系陶瓷的结构与电性能进行表征。结果表明:所制备的NKBTSM陶瓷样品均为单一的钙钛矿结构。Sr和Mn的复合掺杂促进了晶粒的长大,并提高了致密度。与纯NKBT陶瓷相比,掺杂Sr和Mn能提高陶瓷的压电常数d33、机电耦合系数kp和机械品质因子Qm,降低陶瓷的介质损耗tanδ。该系陶瓷具有介电弛豫特性,弥散因子随x的增加先增大后减小。综合考虑:x=1.00%陶瓷的电学性能最佳:d33=152pC/N,Qm=195,kp=28.66%,εr=701,tanδ=2.84%。     

Dielectric and optical properties of Ni doped Na0.5Bi0.5TiO3

Polycrystalline Ni doped Na_.5Bi_0.5TiO₃ samples (Na_0.5Bi_0.5)Ti_1-xNi_xO_3, (x?=?0.5, 0.10, 0.15) have been prepared by solid state reaction. The appearance of the additional peak in X-ray diffraction pattern indicates the ordering of Ti⁴⁺ and Ni²⁺ ions. Polygonal grains are converted into flakes with an increase of Ni concentration. Replacement of Ti⁴⁺ by Ni²⁺ strongly modifies the relative contribution of two peaks in the Raman bands within 200–400?cm^?1. Oxygen vacancy is observed in X-ray photoelectron spectrum to maintain charge neutrality due to aliovalent doping. Broad diffuse phase transition centered at the dielectric constant maximum indicates relaxor behaviour. Comparison between impedance and electric modulus spectrum suggests non-Debye relaxation. The ac conductivity follows the power law with the frequency exponent lies 0.52???0.72. The generation of holes by divalent Ni dopant at tetravalent Ti sites enhances optical band gap.     

Dielectric and impedance spectroscopy of Bi(Ca0.5Ti0.5)O3 ceramic

Bismuth calcium titanate (BiCa_0.5Ti_0.5O₃) ceramic, fabricated by a ceramic processing technique, has been characterized using a variety of experimental techniques. Analysis of basic crystal structure using X-ray diffraction data exhibits the orthorhombic system. Measurements and detailed analysis of some electrical parameters (i.e.,dielectric constant, loss tangent (energy loss), electrical impedance and modulus, conductivity, etc.) of Bi(Ca_0.5Ti_0.5)O₃ in a wide range of frequency (10³–10⁶ Hz) and temperature (30–500 °C) have provided some interesting and useful data and results on structure–properties relationship, conduction mechanism, etc.The role of interface, space charge polarization and Maxwell–Wagner dielectric relaxation in getting high dielectric constant of the material at low frequencies and high temperatures has been discussed. Study of temperature dependence of Nyquist plots clearly shows the contributions of grains in resistive and capacitive properties of the material. The frequency of the applied electric field and temperature strongly affect the dielectric (permittivity and dissipation of energy) and electrical (impedance, electrical modulus and conductivity) characteristics of the material.     

Dielectric properties of CuO-doped La2.98/3Ba0.01(Mg0.5Sn0.5)O3 ceramics at microwave frequency

The microwave dielectric properties of La_2.98/3Ba_0.01(Mg_0.5Sn_0.5)O₃ ceramics prepared by the conventional solid-state method were investigated for application in mobile communication. A 100 °C reduction of the sintering temperature was obtained by using CuO as a sintering aid. A dielectric constant of 20.0, a quality factor (Q × f) of 50,100 GHz and a temperature coefficient of resonant frequency τ_f of −78.3 ppm/°C were obtained when La_2.98/3Ba_0.01(Mg_0.5Sn_0.5)O₃ ceramics with 0.25 wt.% CuO were sintered at 1500 °C for 4 h.     

Solid state metathesis synthesis of BaTiO3, PbTiO3, K0.5Bi0.5TiO3 and Na0.5Bi0.5TiO3

A solid state metathesis approach has been applied to synthesize perovskite oxides such as BaTiO₃, PbTiO₃, K_0.5Bi_0.5TiO₃ and Na_0.5Bi_0.5TiO₃, these were characterized by powder XRD, IR and energy dispersive spectra (EDS). Potassium titanium oxalate and metal chlorides are used as the starting materials. X-ray analysis shows the formation of a single phase with tetragonal structure for BaTiO₃, PbTiO₃, K_0.5Bi_0.5TiO₃ and a monoclinic structure for Na_0.5Bi_0.5TiO₃. The Infrared spectra of these compounds show the characteristic band due to Ti–O octahedron for all the compounds. The EDS spectra show the relative ratio of the metal ions. The morphology of synthesized compounds was obtained from SEM measurements.     

Hydrothermal synthesis and characterization of Na0.5Bi0.5TiO3 microcubes

Na_0.5Bi_0.5TiO₃ microcubes with smooth faces and clear, well-defined edges have been successfully prepared for the first time by a simple hydrothermal method without any surfactants. The as-prepared Na_0.5Bi_0.5TiO₃ microcubes showed an obvious emission band compared with nanoparticles, which is attributed to the different NBT morphology and size.     

Co2O3掺杂对(Na0.8K0.2)0.5Bi0.5TiO3陶瓷结构与电性能的影响

采用传统固相法制备了(Na0.8K0.2)0.5Bi0.5TiO3+xmol%Co3+(BNKT-xCo,x=0-8)无铅压电陶瓷,研究了Co2O3掺杂对BNKT陶瓷的显微结构与电学性能的影响。研究表明:适量的Co2O3掺杂促进了晶粒生长,纯BNKT陶瓷样品在介电温谱上有2个介电反常峰Td和Tm,Co2O3掺杂后使所有陶瓷样品的第一个介电反常峰Td消失,表明Co3+抑制铁电-反铁电相变。室温下样品的介电、铁电和压电性能表明Co2O3起硬性掺杂效应。当x=7时陶瓷样品电性能最佳,其中机械品质因子Qm=498,介电损耗tanδ=2.3%(1kHz),压电常数d33=103pC/N,平面机电耦合系数kp=27%。     

Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–BaTiO3–SrTiO3陶瓷的准同型相界与电性能

采用固相法制备了 Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3–BaTiO3–SrTiO3（NBT–KBT–BT–ST）陶瓷,该体系是按（1–2x）（0.8NBT–0.2KBT）–x（0.94NBT–0.06BT）–x（0.74NBT–0.26ST） （x = 0.10、0.20、0.25、0.30、0.35、0.40、0.45）组合而成的,研究了该系陶瓷的结构与电性能。结果表明：所有样品都处于三方–四方准同型相界区域。该系陶瓷在准同型相界附近表现出了优异的压电性能,压电常数 d33、机电耦合系数 kp和剩余极化强度 Pr随 x 的增加先升高后降低,其中 x=0.35 陶瓷的电性能最佳：d33= 210 pC/N,kp= 0.319,Pr= 39.3 μC/cm2,Ec= 20.2 kV/cm,是一种良好的无铅压电陶瓷候选材料。依据准同型相界组成的线性组合规律来寻找具有优异压电性能的 NBT–KBT–BT–ST 陶瓷准同型相界组成是可行的。     

Reduced dielectric loss and high piezoelectric constant in Ce and Mn co-doped BiScO3-PbCexTi1-xO3-Bi(Zn0.5Ti0.5)O3 ceramics

MnO₂-doped 0.99(0.36BiScO₃-0.64PbTi_1-xCe_xO₃)-0.01Bi(Zn_0.5Ti_0.5)O₃ (BS-PTC-BZT-MnO₂) ceramics are fabricated by the solid-state method. Here, it's firstly reported that Ce element can reduce dielectric loss (tan δ) and suppress the decrease of piezoelectric constant (d₃₃) simultaneously. Effects of Ce contents on the structure and electrical properties of BS-PTC-BZT-MnO₂ ceramics are studied. The ceramics (x?=?0.02) with MPB (rhombohedral-tetragonal) possess low dielectric loss (tan δ?=?1.36%, 1?kHz) and high piezoelectric constant (d₃₃ =?360 pC/N) simultaneously, which is superior to most reported BS-PT. Besides, excellent comprehensive properties including high Curie temperature (T_C =?422?°C), large dielectric constant (?_r =?1324), and high remnant polarization (P_r =?35.1?µC/cm²) are obtained. Asymmetric S-E and P-E hysteresis loops indicate that defects and oxygen vacancies are induced by multi-valence elements (Ce and Mn), which is the origin for reducing tan δ. In addition, good thermal stability of piezoelectric and dielectric properties is observed. These results indicate that Ce and Mn co-doped BS-PTC-BZT-MnO₂ ceramics can be well applied as power electronic devices under high temperature.     

Dielectric properties of Bi-doped Ba0.8Sr0.2TiO3 ceramic solid solutions

Bismuth-doped barium–strontium–titanate ceramics of the formula (Ba_0.8Sr_0.2)_(1−1.5y)Bi_yTiO₃ were prepared using a conventional solid-state reaction method. The structure, dielectric properties, and ferroelectric relaxor behaviour of all compositions were thoroughly investigated. The findings revealed a broad dielectric anomaly and a shift in dielectric maxima towards higher temperatures with increasing frequency. The diffuseness degree indicator γ was about 1.68, and dielectric relaxation was noted to follow the Vogel–Fulcher relationship, with T_f=185 K, f₀=1.18×10¹⁰ Hz, and Ea=0.35 eV, which further supported the spin-glass-like properties of BBSTs. The latter were also noted to display significant ferroelectric relaxor behaviour that could be attributed to the presence of Bi³⁺ doping ions. The degree of relaxation behaviour was noted to increase with the increase in bismuth concentration. Raman spectra were investigated as a function of temperature, and the findings confirmed the results from X-ray and dielectric measurements. Among the compositions assayed in this solid solution, 10% Bi-doped Ba_0.8Sr_0.2TiO₃ yielded promising relaxor properties that make it a strong candidate for future industrial application in the production of efficient and eco-friendly relaxor ferroelectric materials.     

Dielectric behaviors of Ba(Mg1/3Nb2/3)O3 modified (Na0.5K0.5)NbO3 ceramics

The effects of Ba(Mg_1/3Nb_2/3)O₃ additives to lead-free (1-x)(Na_0.5K_0.5)NbO₃-xBa(Mg_1/3Nb_2/3)O₃ ceramics have been investigated. XRD patterns, SEM images and Raman spectra have been used to discuss phase structure transitions and microstructure. The dielectric behavior has been also investigated by using the empirical law, the Curie-Weiss law and the spin-glass model. Results show the diffused phase transition behavior to be enhanced by increasing Ba(Mg_1/3Nb_2/3)O₃ addition and the dielectric behavior to be changed to the more short range order of relaxor ferroelectric. Barium and Magnesium cations are suggested to enter into the cation sites and induce the changes of lattice structure, microstructure, compositional fluctuation, cation disorder and correlation of neighboring cluster-sized moments.     

Large strain response in Li/Nb co-doped Bi0.5(Na0.8K0.2)0.5TiO3 lead-free piezoceramics

A series of (Bi_0.5Na_0.4K_0.1)Ti_0.98Nb_0.02O₃-xLi lead-free ceramics were fabricated using the solid-state reaction technique. The effects of Li/Nb cations on the structural and electrical properties of the ceramics were investigated. All the sintered ceramics exhibited pure perovskite structure and the average grain size increased slightly with increasing the Li content. Shape of the P-E loops illustrated the relaxor characteristic of all the samples. A giant strain of 0.4% was obtained at 60 kV/cm at x = 0.01 and the corresponding normalized strain was up to 683 pm/V, moreover, the strain exhibits excellent fatigue-resistance behavior. The giant strain can be attributed to the ferroelectric-relaxor phase transition under external driving electric field. These results indicate the sintered Li/Nb co-doped lead-free ceramics can be promising candidate for actuator applications.     

Complex structural contribution of the morphotropic phase boundary in Na0.5Bi0.5TiO3 - CaTiO3 system

The correlation between structure and dielectric properties of lead-free (1-x)Na_0.5Bi_0.5TiO₃ - xCaTiO₃ ((1-x)NBT - xCT) polycrystalline ceramics was investigated systematically by X-ray diffraction, combined with impedance spectroscopy for dielectric characterizations. The system shows high miscibility in the entire composition range. A morphotropic phase boundary (MPB), at 0.09?≤?x?<?0.15 was identified where rhombohedral and orthorhombic symmetries coexist at room temperature. The fraction of orthorhombic phase increases gradually with x in the MPB region. Dielectric measurements reveal that the relative permittivity increase with addition of Ca²⁺. This behavior is unusual with this kind of doping. A thermal hysteresis occurred only in the MPB composition which varies in a non-monotonically manner with x, detected by dielectric properties. This phenomenon is related to the crystalline microstructure by a linear relationship between the fraction of each phase and dielectric properties, and, more precisely, to the strong interaction between rhombohedral and orthorhombic phases.     

An experimental and theoretical investigation on relaxor behavior and local correlations in xBi(Zn0.5Ti0.5)O3-(1-x)BaTiO3 ceramics

Relaxor behavior and local correlations in perovskite structured xBi(Zn_0.5Ti_0.5)O₃-(1-x)BaTiO₃ (xBZT-(1-x)BT,0.30?≥x?≥?0.10) ceramics are investigated by both experimental and theoretical Ab initio molecular dynamics calculations. For 0.30?≥x?≥?0.10, xBZT-(1-x)BT ceramics show typical relaxor behavior. For x?≥?0.20, the J-E loops show “whale” shape and no saturated P-E loops are observed even near the polar nanoregions (PNRs) freezing temperature T_f (135 K–146?K), indicating that long range polar order (ferroelectric domian) does not exist in these samples, and the PNRs locate at nonergodic state with temperature decreasing. The partial pair distribution function (PDF) results show that Bi atoms are very sensitive to the local B site occupancy and have pronounced trend to displace toward neighboring Zn atoms. The Bi-Zn displacement coupling will enhance the local polarization and stabilize the PNRs even at higher temperature. The dipole correlation function (DCF) results show that the Bi dipoles only correlate with their nearest Ti neighbors and the polarization correlation with the second-nearest Ti neighbors is negligible. No existence of long range polar order in xBZT-(1-x)BT (x?≥?0.20) can be attributed to the Bi displacement influenced highly by the random distribution of Zn atoms and the dominated Bi-Ti dipole correlations only existing within the nearest Bi-Ti neighbors.     

The phase formation process of Bi0.5(Na0.8K0.2)0.5TiO3 thin films prepared using the sol-gel method

Lead-free Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ (abbreviated as BNKT) thin films were grown on Pt(111)/Ti/SiO₂/Si substrates using a sol-gel/spin coating technique and were then annealed at different temperatures (350 °C, 550 °C, 750 °C and 850 °C). Analysis of the XRD patterns and FT-IR spectra were used to determine the main reactions and the phase formation process of BNKT thin films during the sol-gel process. The results show that the dielectric constant of the thin films attains a maximum at a set temperature and then decreases at higher annealing temperatures, which can be attributed to phase formation and transformation. Moreover, the morphologies of the BNKT thin films improve with the increase in grain size and the formation of distinct grain boundaries. Furthermore, through increasing the pH of the precursor solutions, the size of the sol-gel colloidal particles increases slightly and the grains formed from the corresponding solutions tend to be small and uniform.     

The influence of sintering aids for Nd(Mg0.5Ti0.5)O3 microwave dielectric ceramics properties

The influence of various sintering aids on the microwave dielectric properties and the structure of Nd(Mg_0.5Ti_0.5)O₃ ceramics were investigated systematically. B₂O₃, Bi₂O₃, and V₂O₅ were selected as liquid-phase sintering aids to lower the sintering temperature. The sintered Nd(Mg_0.5Ti_0.5)O₃ ceramics are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microwave dielectric properties. The sintering temperature of Nd(Mg_0.5Ti_0.5)O₃ microwave dielectric ceramics is generally high, about 1500 °C. However, the sintering temperature was significantly lowered about 175 °C from 1500 °C to 1325 °C by incorporating in 10 mol% B₂O₃ and revealed the optimum microwave dielectric properties of dielectric constant (_r) value of 26.2, a quality factor (Q × f) value of 61,307 (at 9.63 GHz), and τ_f value of −45.5 ppm/°C. NdVO₄ secondary phase was observed at 10 mol% V₂O₅ addition in the sintering temperature range of 1300–1325 °C, which led the degradation in microwave dielectric properties. The microwave dielectric properties as well as grain sizes, grain morphology, and bulk density were greatly dependent on sintering temperature and various sintering aids. In this study, it is found that Nd(Mg_0.5Ti_0.5)O₃ incorporated with 10 mol% B₂O₃ with lower sintering temperature and excellent dielectric microwave properties may be suggested for application in microwave communication devices. The use of liquid-phase sintering, the liquid formed during firing normally remains as a grain boundary phase on cooling. This grain boundary phase can cause a deterioration of the microwave properties. Therefore, the selection of a suitable sintering aid is extremely important.