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Temperature stable microwave dielectric materials xBaTiO-(1 − x)BaSmTiO were produced through a conventional solid-state reaction procedure in the work. The structural and microwave dielectric properties of the ceramics were determined with the purpose of finding a microwave ceramics with high dielectric constant (ε), high quality factor (Q × f) and zero temperature coefficient of resonant frequency (τ). Experimental results showed that BaTiO additions affected grain growth and densification, the grain size distribution, and tuned the dielectric properties of the produced ceramics. The amount of BaTiO strongly influenced the densification and the microstructure (i.e. grain shape and size) of the produced ceramics. Analysis of the experimental results suggests that the microstructural features can be correlated to the dielectric properties of these ceramics. Accordingly, the dielectric constant (ε) and the temperature coefficient of resonant frequency (τ) of the produced BaSmTiO ceramics can be tuned with the amount of BaTiO additions and the sintering process parameters. The best dielectric properties were achieved for BaSmTiO ceramics with 15% BaTiO (ε = 66, Q×f = 15,730 GHz and τ ≈ 0 ppm/°C). Experimental results suggest that BaTiO doping improves the dielectric properties of the sintered BaSmTiO perovskite ceramics, which are further enhanced by doping with BaTiO in small amounts. However, further increase of BaTiO content jeopardizes them. [ABSTRACT FROM AUTHOR]

Dense AlN ceramics with a thermal conductivity of 180W/m·K were obtained at the sintering temperature of 1750 °C using CaF2 and YF3 as additives. At temperatures below 1650 °C, the shrinkage of AlN ceramics is promoted by liquid (Ca,Y)F2 and Ca12Al14O32F2. Liquid CaYAlO4 mainly improves the densification of the sample when the sintering temperature increases to 1750 °C. The formation of liquid (Ca,Y)F2 at a relatively low temperature results in homogeneous YF3 distribution around the AlN particles, which benefits the removal of oxygen impurity in the AlN lattice, and thus a higher thermal conductivity. [Copyright &y& Elsevier]

Effects of Li2O on the densification and the thermal conductivity of AlN ceramics sintered at a low temperature were studied by using Li2CO3, CaF2 and Y2O3 as additives. DTA and XRD were employed to identify the formation of the liquid and the changes of the phase compositions during the sintering. SEM and TEM were used to observe the microstructures of AlN specimens sintered at 1650 °C. The results show that Li2O is an effective sintering aid, leading to high densification and high thermal conductivity at low sintering temperatures. AlN specimens with full densification and thermal conductivity were achieved with Li2O addition. The high densification comes from the promotion of the liquid containing Li and CaYAlO4. The high thermal conductivity is attributed to the purification of the AlN lattice, the enhancement of the density and the elimination of some grain-boundary phases. [Copyright &y& Elsevier]