Preparation And Properties Of BST Nano-powder And BST/MgO Multiphase Ceramic Material

Barium strontium titanate (BST) materials have characteristics such as high dielectric constant, small dielectric loss and low Curie temperature. The paraelectric barium strontium titanate has the potential applications in the fields of cell capacitor of the dynamic random access memory devices (DRAMs), tunable microwave device applications. Recently, Investigation of BST has been continued growth.In this paper, with the starting materials of Ba(NO₃)₂-Sr(NO₃)₂-TiO(NO₃)₂ -C₆H₈O₇.H₂O, nano-particle Ba_o.7Sr_o.3TiO₃ powders were prepared by low-temperature combustion synthesis of sol at the first time. The effects of the molar ratio of citric acid and metal ions, pH value of the sol and burning temperatures on the particle size were investigated by the cross experiment method. The optimum fabrication process parameters were as follows, the molar ratio of citric acid to metal ions is 1.5 to 1, the pH value is 7 and the thermal treatment temperature is 650°C.Ba_o.6Sr_o.4TiO₃ ceramic samples were fabricated by conventional ceramic processing with a starting powders prepared by low-temperature combustion synthesis of sol. The sample sintered at 1300°C has a higher dielectric constant value of 5074 and a lower dielectric loss value of 0.0025 at 10kHz and 25 °C.The study on ferroelectric phase shift materials is very important in the fields of phase shifter. The excellent dielectric properties of BST for phase shifter can be obtained by adding some second phase to form multiphase materials. Adding magnesia into BST can reduce the dielectric constant and dielectric loss of BST. In this paper, Ba_o.6Sr_o.4TiO₃/MgO multiphase ceramic material was prepared using Ba_o.6Sr_o.4TiO₃ c powders fabricated by low-temperature combustion synthesis of sol and 50wt% MgO nano- powders as starting materials. The results show that the samples sintered at 1200°C and 1250°C have the dielectric constant values of 157 and 161, the dielectric loss values of 0.0018 and 0.00225 at 100kHz and 25°C. The tunability of the material reached more than 20% under applying lkV/mm dc bias field at 10kHz. The result is higher than any other results of the same materials. The higher tunability of the material can meet the requirement of ferroelectric phase shift materials completely.