Effect of temperature on nonlinear electrical behavior and dielectric properties of (Ca, Ta)-doped TiO2 ceramics

TiO₂ ceramics doped with 0.75 mol% Ca and 2.5 mol% Ta were sintered at different temperatures ranging from 1300 to 1450°C. The effects of sintering temperature on the microstructure, nonlinear electrical behavior, and dielectric properties of the ceramics were studied. The sample sintered at 1300°C exhibits the highest nonlinear coefficient (5.5) and a comparatively lower relative dielectric constant.     

Microstructure and microwave dielectric properties of TiO2-doped pseudo-wollastonite ceramics

The effects of TiO₂ addition on the densification, microstructure and microwave dielectric properties of pseudo-wollastonite ceramics (α-CaSiO₃) have been investigated. The X-ray diffraction (XRD) patterns results indicate that samples exhibit a two-phase system, which has a wollastonite-structured α-CaSiO₃ primary phase associated with a CaTiSiO₅ minor phase. However, the TiO₂ addition undermines the microwave dielectric properties because of the poor quality factor of the secondary phase of CaTiSiO₅, which can inhibit the growth of α-CaSiO₃ grains by surrounding their boundaries. The α-CaSiO₃ ceramics containing 2 wt% of TiO₂ sintered at 1,300 °C showed excellent microwave dielectric properties: an ε _r value of 7.86, a quality factor Q × f value of 16,491 GHz, and a τ _f value of 0.76 ppm/ °C.     

Giant dielectric permittivity of Ca and Sb-co-doped TiO2 ceramics

The continuous development of microelectronic devices with integrated functions has led to an increasing interest in the development of dielectric ceramics with high dielectric constant, low dielectric loss, good frequency, and temperature stability. In this work, (Ca, Sb)-co-doped TiO₂ (CSTO) ceramics were prepared by solid-phase reaction sintering method and their phase structure, microstructure, giant dielectric properties, and mechanism were systematically investigated. The results show that the secondary phase of CSTO ceramic samples appeared when x?≥?4%. The average grain size of CSTO ceramics decreased as the amount of doping increases, and all CSTO ceramics had giant dielectric constants. When the doping amount was x?=?4%, the CSTO ceramics obtained optimum dielectric properties, where ε′ = 2.6?×?10⁵ and tan δ?=?0.10. X-ray photoelectron spectroscopy (XPS) results showed that the giant dielectric origin was mainly due to the Sb⁵⁺ doping that generated electrons inside the material, Ca²⁺ doping that enhanced the generation of vacancies inside the material, and the defective dipole clusters produced that improved the dielectric properties of the CSTO ceramics. This work is critical for the development and deployment of new TiO₂-based giant dielectric ceramics.

     

Microstructure and electrical properties of (Ta, Co, Pr) doped TiO2 based electroceramics

The addition of different dopants affects the densification, mean grain size and electrical properties of TiO₂-based varistor ceramics. This paper discusses the microstructural and electrical properties of (Ta, Co, Pr) doped TiO₂ systems, demonstrating that some of these systems display electrical properties that allow for their use as low voltage varistor. Dopants such as Ta₂O₅ play a special role in the formation of barriers at the grain boundary and in the nonlinear behavior in TiO₂-based systems. The higher values of nonlinear coefficient and breakdown electric field were obtained in the system just doped with Ta₂O₅ and CoO.     

Microwave dielectric characteristics of Mg(Ta1−xNbx)2O6 ceramics

The crystalline phase and the microwave dielectric properties of the Mg(Ta_1−xNb_x)₂O₆ ceramics have been investigated. Combining the positive temperature coefficient of the resonant frequency (τ_f) material (MgTa₂O₆, τ_f = +30 ppm/°C) with the negative one (MgNb₂O₆, τ_f = −70 ppm/°C) can produce the composite with τ_f ∼ 0 ppm/°C. The crystal structure of pure MgTa₂O₆ ceramic is the tetragonal structure. For x = 0.15, the crystal structure of the solid solution was the coexistence of the tetragonal structure and orthorhombic structure. Solid solutions with 0.25 ≦ x ≦ 1 exhibit the orthorhombic structure, which is like the structure of pure MgNb₂O₆ ceramic. The sintered morphologies of Mg(Ta_1−xNb_x)₂O₆ ceramics gradually change from the disk-typed grains (x = 0 and 0.15) to the disk-typed and bar-typed grains coexist (x = 0.35, 0.5, and 0.7), and then reveal the bar-typed grains (x = 0.85 and 1). The densities, dielectric constants (ɛ_r) and τ_f values of Mg(Ta_1−xNb_x)₂O₆ ceramics decrease with the increase of the MgNb₂O₆ content. The quality factor (Q × f) reaches the minimum value at x = 0.15, and then increases with the increase of the MgNb₂O₆ content. The Mg(Ta_1−xNb_x)₂O₆ ceramic with x = 0.25 sintered at 1450 °C exhibits a minimum τ_f value of −0.7 ppm/°C.     

Investigation of the crystal structure and electrical properties of La3+-doped SrBi2Ta2O9 ceramics

The layered-perovskite ferroelectric ceramics of La³⁺-doped SrBi₂Ta₂O₂ (SBT), with the chemical formula of SrBi_{(2 - x)}La _x Ta₂O₉ (SBLT), have been prepared by the conventional mixed-oxide method. The effect of substitution of La³⁺ for Bi³⁺ in the crystal structure and electrical properties of SBT ceramics was explored with the aid of X-ray diffraction, (T) curve and ferroelectric hysteresis loop measurements. The electrical properties such as dielectric constant () and remanent polarization (P _r) showed a dependence on the crystal structure, and both reached maxima of 243 and 25 C cm^–2, respectively, with 6 at % La³⁺ substitution, accompanying the greatest structure change. Theoretical considerations were presented to suggest that the atomic displacements and the crystal deformation implied by the crystal structure change are responsible for the improvement of electrical properties. On the other hand, degradation of fatigue resistance was observed in SBLT ceramics, which is believed to be caused by the chemical environment change of the perovskite layers arising from La³⁺ substitution on Bi³⁺ sites.     

Cr2O3对(Co,Ta)掺杂的SnO2压敏电阻电学特性的影响

研究了Cr对(Co,Ta)掺杂的SnO2压敏材料电学性质的影响.当Cr2O3的含量从0增加到0.15mol%时,(Co,Ta)掺杂SnO2压敏电阻的击穿电压从206V/mm增加到493V/mm;1kHz时的相对介电常数从1968猛降至498;晶界势垒高度分析表明,SnO2晶粒尺寸的迅速减小是样品击穿电压增高、相对介电常数急剧降低和电阻率迅速增大的主要原因.对Cr含量增加引起SnO2晶粒减小的原因进行了解释.掺杂0.15mol% Cr2O3的SnO2压敏电阻非线性系数为24,击穿电压达498V/mm,在高压保护领域有很好的应用前景.     

The abnormal grain growth and dielectric properties of (Nb,Ba) doped TiO2 ceramics

The effect of consolidation pressure and crystallite size of powders crystal phases of TiO₂ on sintered microstructure of TiO₂ ceramics doped with 0.25 mol % Nb and 1.0 mol % Ba were investigated. Also, the development sequence of abnormal grain growth of (niobium, barium) doped TiO₂ ceramics was proposed. The second phases of as-sintered surface were determined. The dielectric properties of Ag-electroded samples were correlated with the resistivity of the bulk (Nb, Ba) doped TiO₂ ceramics. Abnormal grain growth lowered the resistivity of bulk material of (Nb, Ba) doped TiO₂ ceramics, and moved the relaxation frequency of fan δ to high frequency region over 10⁵ Hz. Controlling the sintered microstructures can obtain reasonably good dielectric properties.     

Sintering and dielectric properties of Sr(Bi2Ta2)0.95Ti0.2O9 ceramics

In this study, TiO₂ is used to substitute the Bi₂O₃ and Ta₂O₅ sites of the SrBi₂Ta₂O₉ ceramics to form Sr(Bi₂Ta₂)_0.95Ti_0.2O₉ composition. From the X-ray patterns, the 2θ values shift to higher values as the sintering temperatures increase. At lower sintering temperatures of 1200–1250 °C, the Sr(Bi₂Ta₂)_0.95Ti_0.2O₉ ceramics reveal a two-phase structure, bar-typed grains and disk-typed grains coexist; when 1300 °C is used as the sintering temperature, only the bar-typed grains are revealed. The sintering temperatures also have large influences on the maximum dielectric constants and the Curie temperatures of Sr(Bi₂Ta₂)_0.95Ti_0.2O₉ ceramics.     

Crystal structure and dielectric properties of Ca(0.85)Nd(0.1)TiO(3) - LnAlO(3) ceramics

The microwave dielectric properties of Ca(0.85)Nd(0.1)TiO(3) - LnAlO(3) (Ln = Sm, Gd, Dy, Er) ceramics are investigated in this paper. The structural characteristics of the specimens were evaluated by Rietveld refinement of Xray diffraction (XRD) patterns and high-resolution transmission electron microscopy (HRTEM). Solid solution limits were dependent on the ionic radius of Ln(3+) ions. With the decrease of the ionic radius of the Ln(3+) ions, the thermal stability of the resonant frequency decreases. This can be attributed to the increased level of oxygen octahedral distortion caused by the increase in the B-site bond valence in the ABO(3) perovskite structure. The dielectric constant (K) and the quality factor (Qf) of the specimens were dependent on the polarizability and grain size, respectively.     

Microstructure and microwave dielectric properties of multi-oxide-doped (Zr,Sn)TiO4 ceramics

(Zr_0.8Sn_0.2)TiO₄ (ZST) ceramics were prepared by solid-phase method. The effects of MgO/La₂O₃/Nb₂O₅ doped on the phase composition, microstructure, sintering behavior, and microwave dielectric properties of ZST ceramics were investigated. XRD analysis showed that the major crystalline phase was ZST. Very small amounts of phases, Nb₂O₅ and Mg(Ti₂O₅), were observed when dopants were added, and Nb₂O₅ inhibited the formation of Mg(Ti₂O₅). The results showed that upon adding 7 wt% Nb₂O₅ and small amounts of MgO and La₂O₃ to the ceramics, the permittivity of the ceramics was greatly reduced compared to that of other oxide-doped (Zr_, Sn)TiO₄ ceramic materials, and the Q?×?f value was also increased. The coefficients of thermal expansion of ZST ceramics in this study were within the range reported in the literature. Optimal dielectric properties, ε_r?=?34.78, Q?×?f?=?55,190 GHz (f?=?5.8 GHz), τ_f?=?? 13.86 ppm/°C, and CTE?=?7.0 ppm/°C, were achieved for the sample with 7 wt% Nb₂O₅ sintered at 1330 °C for 2 h.

     

Nonlinear electrical properties and aging characteristics of (NiO, MgO, Cr2O3)-doped Zn-Pr-Co-R (R = Y, Er) oxide-based varistors

The electrical properties and stability of the varistors, which composed of (NiO, MgO, Cr₂O₃)-doped Zn-Pr-Co-R (Y, Er) oxide-based ceramics, were investigated for different additives. The breakdown voltage of the varistors increased in order of NiO→undoped→MgO→Cr₂O₃: 1200→1551→1691→1959 V/cm for ZPCY system and undoped→NiO→MgO→Cr₂O₃: 1024→1041→1500→1668 V/cm for ZPCE system, respectively. The nonlinear coefficient value increased in order of undoped→NiO→MgO→Cr₂O₃: 21→25→38→50 in ZPCY system and NiO→undoped→MgO→Cr₂O₃: 27→32→35→38 in ZPCE system, respectively. In ZPCY and ZPCE systems, the Cr₂O₃-additives most greatly improved the nonlinear properties. In Cr₂O₃-doped system, ZPCY system exhibited higher nonlinear properties than that of ZPCE system. The stability against d.c. accelerated aging stress was higher in Cr₂O₃-additives than in NiO- and MgO-additives for ZPCY system and was higher in NiO-additives than in MgO- and Cr₂O₃-additives for ZPCE system.     

Mg4(Ta1-xVx)2O9陶瓷的烧结特性和微波介电性能

用固相法制备了一系列Mg4(Ta1-xVx)2O9(MTV)陶瓷,研究了V5 取代Ta5 、MTV陶瓷的烧结特性和微波介电性能.用XRD和SEM研究其晶体结构和微观形貌.结果表明:在组分x≤0.3范围内形成了Mg4(Ta1-xVx)2O9连续固溶体.少量V5 取代Ta5 能够使MTV陶瓷的烧结温度从1450℃降至1150℃,但同时品质因数降低.x=0.1,1150℃烧结的Mg4(Ta1-0.1V0.1)2O9陶瓷具有较好的微波介电性能:ε约为11,Q·f值达41000GHz(8GHz).     

Interface effects and defect clusters inducing thermal stability and giant dielectric response in (Ta+Y)-co-doped TiO2 ceramics

Journal of Materials Science: Materials in Electronics - High-performance giant dielectric ceramic materials are essential for the advancement of electronic devices. In this work,...     

Characterization and dielectric properties of Ba5NdZnM9O30 (M=Nb, Ta) ceramics

Ba₅NdZnM₉O₃₀ (M=Nb, Ta) ceramics were prepared by the conventional high temperature solid state reaction route. The sintered samples were characterized by X-ray diffraction and scanning electron microscopy methods. They belong to paraelectric phases of filled tetragonal tungsten bronze structure at room temperature and have high dielectric constants of 282 and 85, combined with low dielectric losses of 0.0048 and 0.0081 at 1 MHz for Nb- and Ta-based ceramics, respectively.     

Structural,dielectric, and electrical properties of cerium-modified strontium manganite ceramics

Journal of Materials Science: Materials in Electronics - A solid-state reaction technique was used to make cerium (Ce) modified strontium manganite SrMn0.9Ce0.1O3 (SMCO). The Goldschmidt's...