Microstructure and dielectric properties of BaZr x Ti1−x O3 ceramics

The crystalline structure and dielectric properties of BaZr _x Ti_1−x O₃ ceramics with x = 0.05, 0.10, 0.15, and 0.20 were investigated. As zirconium increased, the a-axis lattice constant gradually increased, however, the c-axis lattice constant and c/a ratio gradually decreased. When x = 0.20, the crystal structures of the BZT ceramics are very close to cubic, different from the tetragonal structure when x < 0.20. The temperature dependence of the dielectric constant was studied and an enhanced diffuse phase transition behavior is found to be caused by the increased Zr content. The decreases of coercive electric field and remanent polarization were the result of increase of Zr/Ti ratio in BaZr _x Ti_1−x O₃.     

Microstructure and dielectric properties of Ba[Ti1 − x (Ln1/2Nb1/2) x ]O3 ceramics

We have studied the microstructure and dielectric properties of barium titanate-based ceramics containing niobium oxide and rare-earth (Nd, Sm, Gd, Dy, and Tm) oxide additions in a ratio needed for the formation of mixed perovskite solid solutions with the general formula Ba[Ti_{1 ? x} (Ln_1/2Nb_1/2) _x ]O₃. It was found that, after sintering at 1100–1120°C with the use of a zinc oxide-based sintering aid and manganese carbonate additions, the ceramics had a core-shell structure in which the core of the grains consisted of barium titanate and the shell consisted of a barium titanate-based solid solution. The average grain size of the major phase in the ceramics was within 0.7 μm. The ceramics contained additional phases in the form of inclusions which occasionally exceeded 5 μm in size. Their composition was determined. The Nd-, Sm-, and Gd-containing materials were shown to have the greatest potential as a base for the development of new engineering materials of stable groups with high dielectric permittivity for multilayer capacitors with electrodes containing 70% Ag and 30% Pd.     

Structural, transport, magnetic, and dielectric properties of La1−x Te x MnO3 (x = 0.10 and 0.15)

In this study, we have investigated the structure, temperature-dependent resistivity, magnetization, and dielectric properties of La_1?x Te _x MnO_3±δ (x = 0.10 and 0.15). X-ray diffraction analysis confirms the rhombohedral crystal symmetry with space group R $ \overline{3} $ c. For both the samples, the temperature dependence of magnetization plots show paramagnetic-to-ferromagnetic phase transition. The Curie temperature (T _c) and magnitude of magnetization increase with the Te concentration. Field-dependent magnetization produces the asymmetric hysteresis loop that has been attributed to the magneto crystalline anisotropy induced by lattice distortion and the rare earth spin coupling at room temperature. Temperature-dependent resistivity plots exhibit metal–insulator transition (MIT) and charge-ordering state. These plots have been fitted using variable range hopping model, and the density of states [N(E_F)] has been estimated. Magnetoresistance is measured as a function of temperature in the field of 1T, 5T, and 8T. The dielectric constant shows an anomaly near MIT. The dielectric constant exhibits a peaking behavior with the applied frequency and the temperature dependence of dielectric constant attains colossal values at high temperatures.     

Ferroelectric and piezoelectric properties of [(Ba1−3x/2Bix)0.85Ca0.15](Ti0.90Zr0.10)O3 lead-free piezoelectric ceramics

Bismuth-modified barium calcium zirconate titanate ceramics [(Ba_1?3x/2Bi_x)_0.85Ca_0.15](Ti_0.90Zr_0.10)O₃ (BBCTZ) have been prepared by the conventional solid-state reaction method, and effects of Bi content on the electrical properties of BBCTZ ceramics were systematically investigated. BBCTZ ceramics endure a phase transition from the coexistence of rhombohedral and tetragonal phases, a tetragonal phase, to a cubic phase with increasing Bi content. The Curie temperature, the remanent polarization, and the dielectric loss of BBCTZ ceramics gradually decrease with increasing the Bi content. The BBCTZ ceramic with x = 0.0075 exhibits an optimum electrical behavior: d₃₃ ～ 361 pC/N and k_p ～ 40.2%.     

Microstructure and microwave dielectric properties of xSm(Mg0.5Ti0.5)O3–(1 − x)Ca0.8Sr0.2TiO3 ceramics

xSm(Mg_0.5Ti_0.5)O₃–(1 ? x)Ca_0.8Sr_0.2TiO₃ (x = 0.50–0.95) ceramics are prepared by a conventional solid-state ceramic route. The microstructure and microwave dielectric properties are investigated as a function of the x-value and sintering temperature. The single phase solid solutions were obtained throughout the studied compositional range. The variation of bulk density and dielectric properties are related with the x-value. Increasing sintering temperature can effectively promote the densification and dielectric properties of xSm(Mg_0.5Ti_0.5)O₃–(1 ? x)Ca_0.8Sr_0.2TiO₃ ceramic system. With the content of Sm(Mg_0.5Ti_0.5)O₃ increasing, the temperature coefficient of resonant frequency τ _f value decreased, and a near-zero τ _f could be obtained for the samples with x = 0.80. The optimal microwave dielectric properties with a dielectric constant ε _r of 30.1, Q × f of 115,000 GHz (at 8.0 GHz), and τ _f of 8.9 ppm/°C were obtained for 0.80Sm(Mg_0.5Ti_0.5)O₃–0.20Ca_0.8Sr_0.2TiO₃ sintered at 1,550 °C for 3 h, which showed high density and well-developed grain growth.     

Microstructure and enhanced electrical properties of (1−x)(Na0.5K0.44Li0.06)NbO3–x(Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 lead-free ceramics

Environment-friendly lead-free piezoelectric ceramics (1?x)(Na_0.5K_0.44Li_0.06)NbO₃–x(Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)O₃ doped with 1.0 mol% MnO₂ were synthesized by conventional solid-state sintering method. The phase transition behavior and electrical properties of the ceramics is systemically investigated. It was found that all the ceramics formed pure perovskite phase with 0.0 ≤ x ≤ 0.1, and the phase structure of the ceramics gradually transformed from orthorhombic to tetragonal phase with increasing x. Coexistence of the orthorhombic and tetragonal phase is formed in the ceramics with 0.04 ≤ x ≤ 0.06 at room temperature, and enhanced dielectric, ferroelectric and piezoelectric properties are achieved in the two phase’s region. The ceramics in the mixed phase region exhibits the following optimum electrical properties: d ₃₃  = 130–147 pC/N, ε _r  = 642–851, P _r  = 5.51–12.44 μC/cm². The Curie temperature of the ceramics with mixed phase region was found to be 353–384 °C. The significantly enhanced dielectric properties, ferroelectric properties and piezoelectric properties with high cubic-tetragonal phase transition temperatures (T _c ) make the KNLN–xBCZT ceramics showing the promising lead-free piezoelectrics for the practical applications.     

Microstructure and dielectric properties of sintered Li–Nb–Ti–O solid solution ceramics having superstructure

Effects of preparation conditions on the microstructures and periodicity of the superstructure for Li_1+xNb_1–xTi_xO₃ phase M polycrystals were investigated. Obtained specimens, mainly comprised of elongated plate-like grains, and their surfaces were found to be parallel to periodical domains. Sintered materials were found to contain Nb-doped Li₂TiO₃ based solid solution that was one of the end members in the phase diagram of constituent materials. Superperiodicity of phase M was found to be affected by the both chemical compositions and sintering conditions. The dielectric constant increased with increasing of periodicity of superstructures, which could be varied by the amount of Ti concentration. Electronic Publication     

Microstructure and microwave dielectric properties of low-temperature sinterable (1 − x)Ba3(VO4)2–xCaWO4 composite ceramics

Low-temperature-sintered Ba₃(VO₄)₂–CaWO₄ composite ceramics were prepared by cofiring mixtures of pure-phase Ba₃(VO₄)₂ and CaWO₄. The thermo-mechanical analysis revealed that the CaWO₄ in the composite ceramic can significantly promote the densification process and lower the sintering temperature to ~900 °C. The X-ray diffraction results indicated that Ba₃(VO₄)₂ and CaWO₄ phases coexist in the sintered ceramics, and no secondary phases can be detected in the composite, implying the good chemical compatibility between the two phases. The near-zero temperature coefficients of the resonant frequency (τ_f) could be achieved by adjusting the relative content of the two phases owing to their opposite τ_f values. The composite ceramics with 60 wt% CaWO₄ sintered at 900 °C exhibited desirable microwave dielectric properties of the quality factor Q × f ~ 37,000 GHz, dielectric constant ε_r ~ 12, and τ_f ~ ?1.4 ppm/°C.     

Structural refinement,optical and electrical properties of [Ba1−x Sm2x/3](Zr0.05Ti0.95)O3 ceramics

Samarium doped barium zirconate titanate ceramics with general formula [Ba_1?x Sm_2x/3](Zr_0.05Ti_0.95)O₃ [x = 0, 0.01, 0.02, and 0.03] were prepared by high energy ball milling method. X-ray diffraction patterns and micro-Raman spectroscopy confirmed that these ceramics have a single phase with a tetragonal structure. Rietveld refinement data were employed to model [BaO₁₂], [SmO₁₂], [ZrO₆], and [TiO₆] clusters in the lattice. Scanning electron microscopy shows a reduction in average grain size with the increase of Sm³⁺ ions into lattice. Temperature-dependent dielectric studies indicate a ferroelectric phase transition and the transition temperature decreases with an increase in Sm³⁺ ion content. The nature of the transition was investigated by the Curie–Weiss law and it is observed that the diffusivity increases with Sm³⁺ ion content. The ferroelectric hysteresis loop illustrates that the remnant polarization and coercive field increase with an increase in Sm³⁺ ions content. Optical properties of the ceramics were studied using ultraviolet–visible diffuse reflectance spectroscopy.     

Synthesis and dielectric and nonlinear properties of BaTi1 − x Zr x O3 ceramics

We have studied the formation of BaTi_{1 ? x} Zr _x O₃ solid solutions with the perovskite structure. The phase composition, microstructure, and electrical properties of the BaTi_{1 ? x} Zr _x O₃ materials have been investigated. The results demonstrate that their dielectric permittivity (?) and loss tangent (tan δ) decrease with increasing zirconium content. At the same time, their nonlinearity coefficient (n ^R ) remains large (n _R = 30–50%) in relatively low fields (E = 30–50 kV/cm). The present data suggest that the materials studied here are potentially attractive for use in creating nonlinear devices of modern microelectronics.     

Preparation,microstructure, and improved dielectric and nonlinear electrical properties of Na1/2La1/2Cu3Ti4O12 ceramics by sol–gel method

Na_1/2La_1/2Cu₃Ti₄O₁₂ (NLCTO) ceramics were prepared by the sol–gel method (SG) and solid-state method (SS), and the effect of sintered temperature on microstructure and dielectric and nonlinear electrical properties has investigated. The experimental results indicated that NLCTO-SG ceramics sintered at 1090 °C for 10 h showed larger grain size, higher density and more homogeneous microstructure, especially higher dielectric constant up to ca 1.3–1.8 × 10⁴, lower dielectric loss of about 0.057 and better temperature stability than NLCTO-SS counterparts. However, the good low-voltage varistor behavior and the third kind of dielectric relaxation behavior could not be observed from the NLCTO-SS ceramics. The higher dielectric constant of the NLCTO-SG ceramics may be due to the stronger internal barrier layer capacitor (IBLC) effect. Two values of grain activation energy were obtained above room temperature for the first time. The transition temperature of two values was basically coincident with that of sudden changes of the dielectric properties.