Study On Modification Of Barium Titanate Based Ceramics Doped With Thulium And Strontium

BST ceramics have been playing an indispensable role in today’s electronic industry.Driven by the miniaturization and integration of electronic devices,there is a growing demand for improving the dielectric constant and temperature stability.In the early stage,Ba_0.7Sr_0.3Ti_0.9925Tm_0.01O₃（BST）ceramics were prepared by doping rare earth ions Sr and Tm.The dielectric constant of BST ceramics increased to hundreds of thousands,but the dielectric loss is also increased greatly.To prepare the ceramics with high dielectric constant,low dielectric loss and good dielectric temperature stability in this paper,BST@BiScO₃and BST-MgO composite ceramics were prepared by sol-gel and chemical precipitation methods.Then,the effects of BiScO₃and MgO on the microstructure and properties of BST based ceramics were studied by means of coating and multi-phase ceramic modification.Optimize the preparation process of BST-based ceramics:BST-based powders were pressed at a pressure of 25kN by pressure rise rate of 1-2kN/s and kept pressure for 5 min,which can obtain the complete bulks;The optimum temperature of rubber discharging was700°C and kept for 1 h.The optimum sintering temperature of BST,BST@BiScO₃and BST-MgO ceramics were 1380°C,1250°C and 1300°C,respectively.BST@BiScO₃powders was prepared by sol-precipitation method.BST powders was successfully coated with amorphous BiScO₃nanoparticles by transmission electron microscopy.The grain size of BST@BiScO₃ceramics decreased with the increase of BiScO₃content.when the addition was 4 mol%,Tm rich particles were precipitated at the grain boundary of BST@BiScO₃ceramics.With the increase of BiScO₃content,the dielectric constant decreased gradually,but remained above 10000,and the dielectric loss decreased significantly.The Curie peak broadened and shifted to a higher temperature.BST-MgO ceramics had a homogeneous perovskite phase and the high-temperature sintering resulted in MgO entering the BST lattice which was verified by XRD and Raman spectra.Due to the long-range polarization was destroyed,the crystal structure changed from pseudo-cubic phase to tetragonal phase.The grain size of BST-MgO ceramics decreased,and the MgO particles distributed uniformly on the BST grain boundary,which inhibited the grain growth.With the increase of MgO content,the dielectric constant of ceramics decreased gradually.But the dielectric loss decreased significantly which were less than 0.004.In addition,due to the displacement of Mg²⁺and Ti⁴⁺to form oxygen vacancy,the Curie peak moved to lower temperature.