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The effect of ZnO on phase composition, microstructure, thermal and dielectric properties of AlN ceramics was studied. The X-ray diffraction indicated that ZnAl2O4 and ZnO phases were detected in samples. With 0.5 wt% ZnO added, the thermal conductivity of AlN sample increased to 193.7 W/m·K. Whereas, the thermal conductivity dropped sharply due to excess ZnO. Moreover, the addition of ZnO increased the permittivity and altered the relaxation mechanism of AlN ceramics. The fitting data and activation energy from impedance spectroscopy revealed the variation of defect mechanisms in samples. The addition of 0.5 wt% ZnO reduced the concentration of aluminum vacancy in AlN grains to improve thermal conductivity. Nevertheless, excess ZnO dissolved into the AlN lattice and created additional defects, causing the decrease in thermal conductivity and electrical resistivity for AlN ceramics. Overall, suitable addition of ZnO can effectively increase the thermal conductivity and alter the dielectric properties of AlN ceramics. [ABSTRACT FROM AUTHOR]

The effects of hot-pressing sintering on the phase composition, microstructure, thermal and electrical properties of AlN ceramics with CeO 2 –CeF 3 additives were studied. During hot-pressing sintering, high pressure reduced the grain boundary phase CeAlO 3 and decreased the concentration of oxygen in AlN ceramics. The hot-pressing sintered AlN samples had a much higher thermal conductivity of 191.9 W/m·K than pressureless sintered ones because of the great reduction of grain boundary phases and oxygen impurities in AlN ceramic. As the carbon content in hot-pressing sintered sample was very high, carbon contamination led to the decrease in electrical resistivity and changes in polarization mechanisms for AlN ceramics. The relaxation peak in the dielectric temperature spectrum with an activation energy of 0.64 eV for hot-pressing sintered samples was caused by electrons from free carbon at low temperature. Overall, hot-pressing sintering can effectively increase the thermal conductivity and change the electrical properties of AlN ceramics. [ABSTRACT FROM AUTHOR]

The effect of oxidation in air on the phase composition, microstructure, flexural strength and thermal property of AlN ceramics was investigated. Oxidation was found to produce a continuous oxide layer on the surface of AlN samples. The flexural strength and thermal conductivity of AlN ceramics significantly improved after oxidation at 1000 °C and 1100 °C. Residual stress in the AlN ceramic matrix was enhanced by oxidation. The enhanced residual compressive stresses inhibited crack propagation and reduced interfacial thermal resistance, thereby improving the flexural strength and thermal conductivity of AlN ceramics. Electrochemical impedance spectroscopy was further used to analyze the defects in AlN ceramics. The increase in fitting grain resistance revealed a decrease in aluminum vacancy concentration in oxidized AlN sample, which resulted in high thermal conductivity. Therefore, oxidation at a certain temperature is pretty effective to obtain excellent performance for AlN ceramics. [ABSTRACT FROM AUTHOR]

Ba5LaMgNb9O30 ceramics with the addition of Li3NbO4 sintered under nitrogen atmosphere were synthesized and characterized. The phase structure, microstructure, dielectric properties and impedance spectroscopy of the prepared ceramics were investigated. All samples showed a diffuse phase transition and the diffuse exponent γ was calculated. With the addition of Li3NbO4, Li+ could enter the C-sites of BLMN ceramics, which modified the composition of the tungsten bronze structure and improved the performance. Results show that addition of Li3NbO4 decreased the sintering temperature of BLMN ceramics to 1050 °C and improved dielectric properties of nitrogen-sintered BLMN ceramics. Impedance spectroscopy analysis indicated that the performance for nitrogen-sintered ceramics was comparable to air-sintered samples at the temperature below 400 °C. The dielectric properties of BLMN ceramics were influenced by the amount of Li3NbO4, and the 15 wt% Li3NbO4-added BLMN ceramic sintered at 1050 °C in nitrogen for 3 h showed good dielectric properties at 1 MHz of εr = 122.19, tanδ = 0.00686 and τε = −631 ppm/°C. The Li3NbO4-added BLMN ceramics have application potential for the multilayer ceramic capacitors co-fired with base metal electrode. [ABSTRACT FROM AUTHOR]

Abstract The effects of two-step sintering on the microstructure, mechanical and thermal properties of aluminum nitride ceramics with Yb 2 O 3 and YbF 3 additives were investigated. AlN samples prepared using different sintering methods achieved almost full density with the addition of Yb 2 O 3 –YbF 3. Compared with the one-step sintering, the grain sizes of AlN ceramics prepared by the two-step sintering were limited, and the higher flexural strength and the larger thermal conductivity were obtained. Moreover, the electrochemical impedance spectroscopy of AlN ceramic was associated with thermal conductivity by analyzing the defects and impurities in AlN ceramics. The fitting grain resistance and the activation energy for the grain revealed the lower concentrations of aluminum vacancy in the two-step sintered AlN ceramics, which resulted in the higher thermal conductivity. Thus, mechanical and thermal properties for AlN ceramics were improved with Yb 2 O 3 and YbF 3 additives sintered using two-step regimes. [ABSTRACT FROM AUTHOR]

(Ba 0.6 Sr 0.4 ) 0.85 Bi 0.1 TiO 3 (abbreviated as BSBT) ceramics doped with x wt% Zn 2 P 2 O 7 ( x  = 0, 1, 5, 10, 15) were synthesized. The influence of Zn 2 P 2 O 7 on microstructures and electrical properties of BSBT ceramics were studied. Microstructural observation indicated that Zn 2 P 2 O 7 doping could inhibit the growth of grain and improve the microstructure homogeneity of BSBT ceramics. Dielectric measurements exhibited a relaxor-like characteristic for all samples. Breakdown strength measurements indicated that undoped BSBT ceramics owned a breakdown strength of 122 kV/cm. However, with increasing Zn 2 P 2 O 7 content, the breakdown strength enhanced monotonously, and the maximum breakdown strength reached 326 kV/cm at x  = 15. Meanwhile, the energy storage efficiency was improved greatly by Zn 2 P 2 O 7 addition. The results suggest that BSBT ceramics doped with Zn 2 P 2 O 7 could be taken for a candidate for energy storage applications. In addition, the correlation between energy storage efficiency and interface polarization was qualitatively discussed by complex impedance spectra. [ABSTRACT FROM AUTHOR]

The phase composition, microstructure, dielectric properties and breakdown strength of (Mg 0.9 Zn 0.1 ) 2 (Ti 1− x Mn x )O 4 ceramics synthesized using a conventional solid-state reaction were investigated. The substitution of Ti 4+ by Mn 2+ can form a single spinel phase and result in a homogenous microstructure, which improves breakdown strength and reduces dielectric loss. Impedance spectroscopy results show that grain and grain boundary exhibit similar impedance properties and that the Schottky barrier in the grain boundary cannot be observed. When the x value is equal to 0.01, (Mg 0.9 Zn 0.1 ) 2 (Ti 1− x Mn x )O 4 ceramics with a high breakdown strength of 102 kV/mm (at 0.2 mm) and a low dielectric loss of 5.3×10 −5 (at 6 GHz) can be obtained, which are beneficial in the development of high voltage solid-state pulse-forming lines. [ABSTRACT FROM AUTHOR]

Dense (1 − x) La[Al 0.9 (Mg 0.5 Ti 0.5) 0.1 ]O 3 – x CaTiO 3 ceramics were synthesized via solid-state reaction. The crystal structure and microwave dielectric properties of the ceramics were systematically investigated. Rietveld refinement revealed that when x ≤ 0.2, the ceramics had a rhombohedral structure with an R-3c space group. When x ≥ 0.5, the ceramics had an orthorhombic structure with a Pbnm space group. Selected area electron diffraction and Raman spectroscopy analyses proved that the microwave dielectric ceramics had a B-site order, which accounted for the great improvement in microwave dielectric properties. The content of oxygen vacancies was identified through X-ray photoelectron spectroscopy, and the change rule of Q × f was closely related to oxygen vacancy content. The perturbation of A-site cations had an important influence on dielectric constant. Specifically, with the increase in Ti4+ content, the perturbation effect of the A-site cations was enhanced and dielectric constant increased. When x = 0.65, the temperature coefficient of resonant frequency of the (1 − x) La[Al 0.9 (Mg 0.5 Ti 0.5) 0.1 ]O 3 – x CaTiO 3 microwave dielectric ceramics was near zero. The optimal microwave dielectric properties of 0.35LaAl 0.9 (Mg 0.5 Ti 0.5) 0.1 O 3 –0.65CaTiO 3 were ε r = 44.6, Q × f = 32,057 GHz, and τ f = +2 ppm/°C. [ABSTRACT FROM AUTHOR]

Ba 2 ZnSi 2 O 7 ceramic was prepared by conventional solid-state method and sintering under four different atmospheres (air, O 2 , N 2 , and N 2 –1 vol% H 2). The Ba 2 ZnSi 2 O 7 ceramic exhibited a single phase under air, O 2 , and, N 2 , whereas two phases (including BaSiO 3 impurity) were observed under the N 2 –1 vol% H 2 atmosphere due to Zn2+ evaporation. Dielectric loss was proportional to oxygen partial pressure due to the conduction mechanism of dominant holes. The Ba 2 ZnSi 2 O 7 ceramic exhibited good microwave dielectric properties (ε r = 8.3, Q × f = 27200 GHz, τ f = −41.5 ppm/°C) under the N 2 –1 vol% H 2 atmosphere, making it a novel candidate with good anti-reductive characteristics for base metal electrode–multilayer ceramic capacitor applications. [ABSTRACT FROM AUTHOR]