Effect of CuO on the sintering and dielectric characteristics of (Ba1−x Sr x ) (Ti0.9Zr0.1)O3 ceramics

In order to lower the temperature required to density (Ba_1–x Sr _x ) (Ti_0.9Zr_0.1) O₃ (BSTZ-series) and to avoid the formation of a low dielectric constant phase, copper oxide is added as liquidphase promotor after BSTZ-series are calcined. Thea-axis lattice constant at room temperature elongates with both increasing amount of CuO added and higher sintering temperature, while thec-axis lattice constant elongates only slightly under the same condition. The dielectric constant increases with sintering temperature. However, for different amounts of CuO added, the dielectric constant increases with increasing amount of CuO at lower sintering temperatures (below 1100°C). When a higher sintering temperature is used (above 1200°C), the dielectric constant reaches a maximum at 1 wt % CuO added, and decreases slightly on further addition of CuO.     

High dielectric tunability of ferroelectric (Ba1−x,Srx)(Zr0.1,Ti0.9)O3 ceramics

(Ba_1?x,Sr_x)(Zr_0.1,Ti_0.9)O₃ (BSZT) ceramics with x = 0, 0.05, 0.15, 0.25, 0.35 and 0.45 were prepared by conventional solid state reaction method. The structural characterization with X-ray diffraction and scanning electron microscopy indicate a monotonical drop in lattice constants and grain size with the increase of Sr concentration. Consequently, the Curie temperature and remnant polarization of the ceramics exhibit a strong compositional dependence. A linear relationship between the Curie temperature and Sr concentration is revealed. At x = 0.45, the BSZT ceramics show substantially high tunability of over 55 % under 20 kV/cm dc electric field with very low dielectric loss value of 0.0025 at room temperature, suggesting the BSZT ceramics could be a promising alternative to traditional (Ba,Sr) TiO₃ ferroelectrics for developing high frequency tunable dielectric devices.     

90‡ domain reversal in Pb(Zr x Ti1−x )O3 ceramics

A simple and direct method has been proposed, which may be used for quantitatively distinguishing the mechanisms of domain reorientation processes in polycrystalline materials. Using this method, the 90 domain reorientation in the Pb(Zr _x Ti_1–x )O₃ ceramic under an electric field was examined through the X-ray diffraction analysis. It was found that polarization switching in the PZT ceramic with a composition near the morphotropic phase boundary, is predominantly controlled by the two successive 90 domain processes rather than only the 180 domain reversal process. Experimental results also indicate that the coercive field of ferroelectric ceramics is related to the cooperative deformation associated with each grain. This cooperative deformation arises from the 90 domain-reversal process.     

Fabrication of perovskite-type Ba(Sn1−x Ta x )O3 ceramics and their power factors

Perovskite-type Ba(Sn_1?x Ta _x )O₃ (0.01 ≤ x ≤ 0.06) ceramics with high relative densities (92.7–94.4 %) were fabricated using the hot isostatic pressing (HIP) method at 1273 K and 196 MPa for 4 h in an atmosphere of argon gas. The lattice parameter decreased slightly with increasing x. From the XPS measurement, the Ta⁵⁺ ion was stable in Ba(Sn_1?x Ta _x )O₃ ceramics and the broad peak of the Ta4f level was the overlap between the Ta⁵⁺4f_5/2 and Ta⁵⁺4f_7/2 levels. Ba(Sn_1?x Ta _x )O₃ ceramics were n-type semiconductors, and their electrical resistivities increased with increasing x. The increase in the electrical resistivity was explained by impurity scattering due to the presence of the Ta ions. The absolute value of the Seebeck coefficient (S) increased with increasing temperature and x. The power factor (S ² σ), which was calculated from electrical conductivity (σ) and the Seebeck coefficient, was ca. 1.0 × 10^?5 W m^?1 K^?2 at x = 0.01.     

Electric-field effect on phase transitions in Pb0.995La0.005[Zr0.9 − y Sn0.1Ti y ]0.99875O3 and Pb0.9975[Zr0.895 − y Sn0.1Ti y Nb0.005]O3 solid solutions

The phase diagrams of PbZrO₃-PbTiO₃-PbSnO₃ solid solutions doped with $ La_{Pb^{2 + } }^{3 + } The phase diagrams of PbZrO₃-PbTiO₃-PbSnO₃ solid solutions doped with and have been constructed using the temperature dependences of their linear dimensions and relative dielectric permittivity measured during zero-field cooling and field cooling. Doping to a level as low as 0.5 at % has a significant effect on the temperature and electric field at which the tetragonal antiferroelectric phase forms. Field cooling of the antiferroelectric solid solutions close in composition to the morphotropic phase boundary consecutively stabilizes two ferroelectric phases. The ferroelectric state produced by field cooling is often inhomogeneously poled and has an asymmetric dielectric hysteresis loop. Original Russian Text ? E.A. Bikyashev, E.A. Reshetnikova, I.V. Lisnevskaya, T.G. Lupeiko, M.I. Tolstunov, 2009, published in Neorganicheskie Materialy, 2009, vol. 45, No. 5, pp. 606–611.     

Fabrication and characterization of high permittivity ceramics in the Ba(Ti1−x−ySnxZry)O3 system

Ceramics of solid solution compositions in the system BaTi_1–x–ySn_xZr_yO₃ have been fabricated using conventional mixed oxide processing routes. Samples with y = 0 or 0.01 exhibited maximum relative permittivities, _r ^max of ~ 65000 and ~ 62000 respectively. The Curie peaks became broader and _r ^max decreased with increasing zirconium substitutions. The Curie temperature decreased linearly from 35°C for y = 0 to –40°C for y = 0.11: for the latter, _r ^max was equal to ~ 20000. The results are interpreted on the basis of microstructural features and on the degree of compositional inhomogeneity in the system.     

Physical and electrical properties of MnO2-doped Pb(Zr x Ti1−x )O3 ceramics

The effects of composition on the physical property change in the phase coexistence region between the tetragonal and rhombohedral phases have been investigated as a function of zirconium concentration, x, for the MnO₂-doped Pb(Zr _x Ti_1–x )O₃ (0.40x0.60) ceramics. The relative amount of phase coexisting between the tetragonal and rhombohedral phases affects greatly both dielectric and piezoelectric properties as a function of zirconium concentration. However, there are no detectable changes between the apparent density and microstructure. Also, in the coexistence region, the relative amount of coexistence of the rhombohedral phase increases with MnO₂ addition. The inflection points of the dielectric constant shift to lower zirconium concentration in proportion to the MnO₂ addition, owing to the substitution effect on the PZT lattice site.     

Crystal structure and dielectric properties of (Pb1−x Ca x )(Zr1−y Sn y )O3 ceramics

There has been an increasing demand for dielectric resonator materials that operate in the microwave frequency range for applications in microwave communications. (Pb,Ca)ZrO₃ ceramics have a dielectric constant (_r), high quality factor (Q) and a small temperature coefficient of resonant frequency (_f). However, basic properties such as its crystal structure, temperature characteristics and the nature of its phase transformation are not yet fully understood. The temperature coefficient of resonant frequency can be controlled fairly well with the temperature coefficient of the dielectric constant. In this paper, we report the results of investigated crystal structure and the dielectric properties of (Pb_1–x Ca _x )(Zn₁– _y Sn _y )O₃ ceramics with the objective of elucidating the relationship between the crystal structure and the dielectric properties. The crystal structure refinement was performed by the Rietveld method. The dielectric properties were measured from-150–350 °C. The phase transformation was analysed from high and low temperature XRD data.     

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 electrical properties of (1 − x)K0.5Na0.5NbO3–x(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 lead-free piezoelectric ceramics

The (1 ? x)K_0.5Na_0.5NbO₃ ? x(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (KNN–BCTZ) lead-free ceramics were fabricated by conventional solid-state sintering technique. The microstructure and electrical properties of the ceramics were investigated. The X-ray diffraction analysis revealed that the ceramics formed a single phase perovskite solid solutions with the symmetry of orthorhombic at x < 0.03. The crystal phase of the ceramics changed from orthorhombic phase to pseudocubic phase when x > 0.04. The coexistence of orthorhombic and pseudocubic (tetragonal) phases was observed near room temperature when 0.03 ≤ x ≤ 0.04. The grains grew up obviously when 2 mol% BCTZ was added, but the grain size was found to reduce gradually with further increasing BCTZ content. The T _C and T _O-T decreased with the increasing BCTZ content. The ferroelectric and piezoelectric properties were abruptly degraded as x ≥ 0.05. Optimum properties (d ₃₃ = 136 pC/N, k _p = 27 %, k _t = 26.5 %, Q _m = 25, P _r = 14.67 μC/cm², E _c = 11.23 kV/cm, T _C = 347 °C, $\varepsilon_{33}^{\text{T}} /\varepsilon_{0} = 8 6 1. 5$ ε 33 T / ε 0 = 8 6 1.5 , tan δ = 0.04) were obtained for the ceramica with x = 0.03.     

Characterization of negative temperature coefficient of resistivity in (Sn1−x Ti x )0.95Sb0.05O2 (x ≤ 0.1) ceramics

Sb-doped SnO₂-based ceramics substituted by a trace of titanium, (Sn_1?x Ti _x )_0.95Sb_0.05O₂ (x ≤ 0.1), were prepared through a wet chemical process polymerized with polyvinyl alcohol. The phase component and related electrical properties of the ceramics were investigated. The results show that all the ceramics have the tetragonal rutile-type SnO₂ crystalline lattice and show typical effect of negative temperature coefficient (NTC) of resistivity. The room-temperature resistivities and NTC material constants can be adjusted widely by changing the Ti content in the ceramics. The investigations by analyzing the electrochemical impedance spectra at various temperatures show that both grain effect and grain-boundary effect contribute to the NTC feature of the ceramics. The conduction mechanisms combining the electron-hopping model and band conduction are proposed for the NTC effect in the ceramics.     

Density variation and piezoelectric properties of Ba(Ti1 − x Sn x )O3 ceramics prepared from nanocrystalline powders

Nanocrystalline powders of tin-doped barium titanate with different concentrations of tin have been synthesized by a combination of solid state reaction and high-energy ball milling. The average particle size of the milled powders as determined from TEM analysis was about 5·96 nm. Analysis of all the milled powders using X-ray diffraction method showed single phase perovskite structure. The density variation of the ceramics with sintering temperature has been studied by sintering the samples at different temperatures. Density variation results show that 1350°C is the optimum sintering temperature for tin-doped barium titanate ceramics. SEM micrographs show high density and increasing trend of grain size with increasing content of Sn. The ferroelectricity decreases with increasing concentration of Sn. The electromechanical coupling coefficient also decreases with increasing Sn content corroborating decreasing trend of ferroelectricity. The bipolar strain curves show piezoelectric properties of the prepared ceramics.     

Structural and dielectric relaxor properties of A-site deficient samarium-doped (Ba1−x Sm2x/3)(Zr0.3Ti0.7O3) ceramics

Rare earth samarium (Sm)-doped barium zirconate titanate (Ba_1?x Sm_2x/3)(Zr_0.3Ti_0.7)O₃ (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were prepared using solid state reaction (SSR) route. The structural and microstructural characterizations of the materials were done by using X-ray diffraction and SEM analysis, respectively. Rietveld refinement technique employed to investigate the details of crystal structure revealed single-phase cubic perovskite structure belonging to space group Pm-3m. Microstructure of the doped ceramics were found to be porous and of irregular shape and size along with aggregative characteristic. FTIR technique was employed to study the influence of additives in ceramics compositions and to investigate the displacement of M–O bonds. Raman spectroscopic study revealed that the substitution of Ba²⁺ ions by Sm³⁺ ions shifted the Raman-active modes toward higher energy, which indicated that these materials undergo an increase in average cubicity with increase in Sm³⁺ ion concentration. The temperature dependence of dielectric properties was investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurement indicated a diffuse type of phase transition (DPT). The broadening in the dielectric permittivity and frequency dependence behavior with increase in frequency indicated a relaxor behavior of these materials. The relaxation strength of these materials was well adjusted by using the Vogel–Fulcher relation.     

Microwave dielectric properties of Ba(Sn x Zn(1−x)/3Nb(1−x)2/3)O3 (0 ⩽ x ⩽ 0.32) ceramics

The dielectric properties of the (1–x)Ba(Zn_1/3Nb_2/3)O₃–xBaSnO₃ (0 x 0.32) composition at microwave frequencies were investigated in this study. With the addition of BaSnO₃, the dielectric Q(Q _d) value of Ba(Zn_1/3Nb_2/3)O₃ (BZN) can be improved and a small temperature coefficient of resonant frequency (_f) can be achieved. When 22.6 mol % of Sn is added to BZN, the characteristics of the Ba(Sn_0.226Zn_0.258Nb_0.516)O₃ ceramics sintered at 1500°C are as follows: dielectric constant _r = 32, _f = + 12 p.p.m.°C¹ and high Q _d value of 9700 at 10 GHz. Based on the classical dispersion theory and the logarithmic mixing rule, the effects with additions of substitutional element of BaSnO₃ on the microwave dielectric properties of Ba(Zn_1/3Nb_2/3)O₃ can be mostly explained.