Fabrication Of Ferroelectric Ceramics By One-step Synthesis

The ferroelectric phase shifter based on the ferroelectric materials (Ba,Sr)TiO3(BST) has been concerned by the phased-array radar antenna technology because of its numerous advantages compared with other kinds of phase shifters.This project was funded by National Natural Science Foundation of China. We focus on the dielectric and temperature properties of ferroelectric material based on BST+MgO (BSTM), and we have developed proper formula to produce ferroelectric ceramics with moderate dielectric constantεr, low dielectric losses tgδ, low temperature coefficient and high dielectric constant tunability.The main research points include:The BST has been synthesized by one step with BaTiO3 and SrTiO3. It has been mixed with 60wt%MgO and some rare earth dopants. The properties have been tested. Comparing with the BSTM produced by conventional method, the new material performs lower sintering temperature, higher density, lower dielectric constantεr, lower high-frequency losses tgδ.We have studied the influence of stuff's particle size distribution to BSTM's physical property, dielectric property and temperature coefficient. We modify the particle size distribution of powder by controlling the hour of ball milling. Experiment Indicated that it is equivalent to modify the the hour of ball milling before presenter and the hour before sintering. While increasing the hour of ball milling, the density andεr increase, the tgδdecreases.We have changed Ba/Sr of BST to study the effects of Ba/Sr on structure and temperature coefficient of BSTM doped with the same rare earth oxides. The results indicated that material have the most desirable properties when Ba/Sr=5.5/4.5: at 10 kHz,εr = 84.45 tgδ= 3.4×10-3, Tunability =11.01%(5kV/mm); and at 3.5GHz,εr = 87.01, tgδ= 4×10-3. At the same time, the material has relative good temperature stability: TCε= -0.482%/℃(-20℃~40℃), temperature coefficient of tenability is -0.836%/℃(-20℃~40℃).