Synthesis of Ca_(1-x)Ba_xZr_4(PO_4)_6 Phosphate Ceramic and Its Thermal Shock Resistance Performance of Near-Zero Thermal Expansion Composition

Ca1-xBaxZr4(PO4)6 (0≤ x ≤1, abbrev CBZP) which belongs to NZP family is a new crystalline solid-solution, it may be possible to utilize the opposite anisotropic behavior of thermal expansion in CaZr4(PO4)6 and BaZr4(PO4)6 to make the magnitude of thermal expansion coefficient be tailored. The main objective of this study was to prepare the material with near-zero thermal expansion and lower anisotropy by adjusting composition, and the single phase CBZP was synthesized by copreciptate methods. The compacts were sintered at temperatures of 1100℃ or 1300℃ with the addition of 3%ZnO or 4%MgO for2h. Their average thermal expansion coefficients from 20~1000℃ and their thermal expansion curves during heating (from 20-1000℃)and cooling(from 1000~-400℃) were measured by TMA compressing method. The results show that some compositions with near-zero thermal expansion are Ca0.85Ba0.15Zr4(PO4)6 when addition of 3%ZnO and CaZr4(PO4)6 when addition of 4%MgO, the linear expansion coefficients is 0.6x 10-/℃ and -0.8x 10-6/℃ respectively. But their thermal expansion curves show hysteresis loops due to microcracking, and the property of thermal shock resistance is not perfect. It can be concluded that it is difficult to minimize their anisotropy by adjusting composition, though the near-zero compositions can be abstained by this means. The useful route of improving their property of thermal shock resistance is properly to suppress the grain growth beyond the transition grain size with an additive (example for SiO2) during the sintering period to decrease microcracking.