The relationship between the microstructure and microwave dielectric properties of zirconium titanate ceramics

Zirconium titanate (ZrTiO4) ceramics have been prepared by the mixed oxide route using small additions of ZnO, Y2O3 or CuO Specimens were sintered mainly at 1400 degrees C and cooled at various rates: water-quench, air-quench, 300 degrees C h(-1), 120 degrees C h -1, 6 degrees C h(-1) and 1 degrees C h(-1). Products prepared with additives exhibited densities of at least 93% of the theoretical value. As the cooling rate after sintering was decreased, the length of the lattice parameter in the b direction was reduced and transmission electron diffraction revealed superlattice reflections associated with cation ordering. For specimens cooled at 1 degrees C h(-1), electron diffraction patterns exhibited features consistent with an incommensurate superstructure in the a direction. The dielectric Q value of rapidly cooled (air-quenched) ceramics was 2000 at 5 GHz. With an increase in the degree of cation ordering the Q value increased to a maxim um of 4400 for specimens cooled at 6 degrees C h(-1). For specimens cooled at the slowest rate (1 degrees C h(-1)) the Q value fell to 2000 due in part to the presence of microcracks and exsolved ZrO2. Diffusion of trivalent impurities (yttria) into the host ZrTiO4 grains also led to a lowering of the Q values. The microwave dielectric properties of zirconium titanate ceramics are sensitive to processing conditions and mircrostructural features. The highest Q values (lowest loss) should be achieved in homogeneous specimens, free of trivalent impurities and lattice defects, in which low Q-value second phases, microcracks and pores are eliminated.