Mi Xiao

Influence of molybdenum substitution on the microwave dielectric properties of CaWO4 ceramic

Dielectric properties of Ca(W1−xMox)4 (xu2009=u20090, 0.02, 0.04, 0.06, 0.08) were investigated at microwave frequency. With the increase of MoO3, the dielectric constant (εr) increased slightly, the value of quality factor (Qu2009×xa0f0) increased considerably and reach the maximum of 79,919xa0GHz, and the temperature coefficient of resonant frequency (τf) shifted for the minus direction. The relationship between the dielectric properties and polarizability, packing fraction and the oxygen bond valence were discussed. The optimum results were obtained when xu2009=u20090.06, the dielectric properties are as follows: εrxa0=xa010.22, Qu2009×u2009f0u2009=u200979,919xa0GHz and τfxa0=xa0−40.39xa0ppm/°C.

Effect of Ni 2+ substitution on crystal structure and microwave dielectric properties for MgZrNb 2 O 8 ceramics

Monoclinic structured Mg1−xNixZrNb2O8 (0u2009≤u2009xu2009≤u20090.12) ceramics were synthesized for the first time through traditional solid-state reaction process and pure phase were obtained in all range. Rietveld refinement was used to analyze the crystal structure. With the increase of Ni2+ substitution amount, εr decreased, Qu2009×u2009f rose first then fell, τf shifted for the positive direction. Bond ionicity, lattice energy and bond energy were separately calculated to investigate the correlations with microwave dielectric properties. Typically, ceramics samples with the composition of Mg0.92Ni0.08ZrNb2O8 sintered at 1280xa0°C for 4xa0h exhibited the optimum microwave dielectric properties: εru2009=u200924.58, Qu2009×u2009fu2009=u200974534.1xa0GHz, τfu2009=u2009−u200949.11xa0ppm/°C, which could be a promising material for application.

Microwave dielectric properties of high Q and temperature stable Li3(Mg1−xNix)2NbO6 ceramics

In this paper, the Li3(Mg1−xNix)2NbO6 (0.02u2009≦u2009xu2009≦u20090.08) ceramics are prepared by a solid state reaction method. The effects of Ni2+ substitution on the microwave dielectric properties, microstructure and sintering properties are investigated systematically. The XRD patterns reveal that all the samples could form solid solution with a single Li3Mg2NbO6 phase in the sintering process. The variation in Qu2009×u2009f values is similar to that in bulk density, and tremendous improvement of Qu2009×u2009f values could be attributed to bigger grains and high densification. Since the more polarizable Mg2+ ion is replaced by the less polarizable Ni2+ ion, the permittivities decrease almost linearly with increasing Ni2+ content. Otherwise, with the x value increase from 0.02 to 0.08, the τf values could be effectively adjusted to near zero, but the decreasing porosity-corrected permittivities would damage the stability of crystal structure, which make the τf values shift toward the negative direction. In general, the Li3(Mg0.96Ni0.04)2NbO6 ceramics sintered at 1175xa0°C for 6xa0h exhibit superior microwave dielectric properties of εru2009~u200915.22, Qu2009×u2009fu2009~u2009126,784xa0GHz, τf ~ −u20092.63xa0ppm/°C, which demonstrate that the ceramics could be selected as a promising low loss and temperature stable material for future application.

Characteristics and microwave dielectric properties of low loss MgZr 0.85 Sn 0.15 Nb 2 O 8 ceramics

MgZr0.85Sn0.15Nb2O8 ceramics with wolframite structure were synthesized through traditional solid-state reaction process. X-ray diffraction and scanning electron microscopy were used to analyze the phase and surface morphology. Bond ionicity, lattice energy and bond energy were calculated separately to investigate the correlations with microwave dielectric properties. Typically, optimal microwave dielectric properties were obtained at 1260xa0°C: εru2009=u200924.91, Qu2009×u2009fu2009=u200994014xa0GHz, τf=−u200943.93xa0ppm/oC.

Crystal structure and microwave dielectric properties of low-permittivity Sr 2 MgSi 2 O 7 ceramic

Low-permittivity Sr2MgSi2O7 ceramics with tetragonal crystal structure were prepared through the conventional solid-state method. X-ray diffraction patterns and scanning electron microscopy were used to analyze the phase and micromorphology of the specimens sintered at temperature from 1260 to 1320xa0°C. The bond ionicity, lattice energy and bond energy of Sr2MgSi2O7 ceramics were calculated to investigate the relationships between microwave dielectric properties and microstructures. Optimum microwave dielectric properties were obtained when the sample was sintered at 1280xa0°C for 4h: εru2009=u20096.85, Qu2009×u2009f0u2009=u200922,530xa0GHz (fu2009=u20099.20xa0GHz), τfu2009=u2009−u200932xa0ppm/°C.

The relationship between the bond ionicity, lattice energy, bond energy and microwave dielectric properties of LaNbO 4 ceramics

LaNbO4 ceramics with single monoclinic fergusonite structure were prepared by the conventional solid-state reaction method at the sintering temperature range of 1275–1375xa0°C. The correlations of bond ionicity, lattice energy, bond energy and the microwave dielectric properties were investigated. The bond ionicity, lattice energy, and bond energy were calculated based on the complex bond theory to analyze the variation trend of dielectric constant (εr), the Qu2009×u2009f0 value and the temperature coefficient of resonant frequency (τf), respectively. LaNbO4 ceramics sintered at 1350xa0°C for 4xa0h possessed excellent microwave dielectric properties: εru2009=u200921, Qu2009×u2009f0u2009=u200955600xa0GHz and τfu2009=u20098xa0ppm/°C.

The effect of Pt x Pb intermetallic metastable phase on the crystal orientation in PZT thin films

In this paper, the crystal orientations of Pb(Zr0.52Ti0.48)O3 (PZT) thin films prepared by sol–gel method were investigated by using various initial annealing temperature in the modified annealing process. The films were put directly into the muffle furnace when the temperature reached at 300–500xa0°C, it’s clear that this modified annealing process made the PZT films presented better (111)-orientation. A PtxPb intermetallic metastable phase was observed by X-ray diffraction, which is considered to be connected with the promotion of the (111) preferred orientation. The PZT thin film with 400xa0°C initial annealing temperature has the maximum (111) diffraction intensity, remanent polarization and dielectric constant.

Microstructure and dielectric properties of BaTiO3–(Bi0.5Na0.5)TiO3–NiNb2O6 ceramics

Abstract0.9BaTiO3–0.1(Bi0.5Na0.5)TiO3–x mol% NiNb2O6 (xu2009=u20090, 0.5, 1.0, 1.5, 2.0, 2.5) ceramics were prepared through traditional solid-state reaction method. The effects of NiNb2O6 doping on the dielectric properties and the microstructure of ceramics were investigated systematically. The results showed that the grain size of the ceramics decreased with the increase of NiNb2O6 doping amount. Ba11(Ni,Ti)28O66+x and Nb2O5 were detected in the X-ray diffractions patterns. The Curie point Tc increased slightly with the increase of NiNb2O6 doping amount. It was interesting to find that the dielectric constant at low temperature of the ceramics first increased and then decreased with the increase of NiNb2O6 concentration. Dielectric temperature stability of 0.9BaTiO3–0.1(Bi0.5Na0.5)TiO3 ceramics greatly depended on NiNb2O6 content. The optimum dielectric properties meeting the X9R specification were obtained in the composition of 0.9BaTiO3–0.1(Bi0.5Na0.5)TiO3 with 1.5xa0mol% NiNb2O6 sintered at 1200xa0°C, εru2009=u20091652 and tanδu2009=u20091.8% at room temperature.