Study On Dielectric Properties Of BST Composite Ceramics And Preparation Of BST Films

Based on the wide use of the barium strontium titanate in the electric tuning microwave components, we prepared BST/MgO and BST/MgO/BZN composite ceramics with ceramic post sintering and studied the material and dielectric properties. Then we prepared the BST films with radio frequency magnetron sputtering and did the elementary research on the films.According to the XRD analysis of BST/MgO, only BST and MgO diffraction peaks were found in the diffraction pattern, the lattice constant of the BST increased as MgO increased, some of Mg replaced the Ti4+ ion. The microstructure of BST/MgO sintered at low temperature was loosen and the compactness was not so good. As the sintering temperature increased, the compactness improved and crystalline became better. The dielectric properties of BST/MgO were good at low frequency, the dielectric constant was between 100 and 500, the lowest loss was lower than 0.005, but it is not apporiate that the content of MgO was too high. At microwave frequency, the dielectric constant was lower than 100, and the loss was between 0.02 and 0.05, so the properties need to be improved.The phase structure of BST/MgO/BZN varied with different sintering temperature. At high sintering temperature, the BZN decompounded and MgO restrained the formation of the BZN and miscellaneous phase. The microstructure of BST/MgO/BZN was good, crystalline grains were big, compactness and crystalline were better than those of BST/MgO. It is better that the sintering tempeture was 1350℃. At low frequency, the dielectric constant was moderate(between 100 and 600), the lowest loss was only 0.002. As the frequency increased, dielectric constant changed little, but loss increased a little linearly. At microwave frequency, the dielectric properties were excellent,εr was about 30 and tgδwas oder of magtitude of 10-4. The dephasing digree of the phase shifter made of BST/MgO/BZN was 360°. So BST/MgO/BZN had the high value in microwave application.BST film was crystalline state after annealing. The longer the sputtering time was the thicker the films were and the higer the BST diffraction peaks were. But according to the SEM analysis, BST crystalline grains grow not so well, grains and grain boundary were illegible and ununiform.