Synthesis and thermal expansion behavior of liquid phase sintered CaZr4(PO4)6–Li2O

Lithium oxide was introduced into the CaZr4(PO4)6 lattice to densify the material to its theoretical density through liquid phase sintering. Although the liquid phase significantly enhanced the densification rate, due to the high solubility of the Li2O liquid phase in the solid, a transient liquid phase was generated, which resulted in microstructures that were extremely sensitive to both composition and processing conditions. It was determined that 1 wt.% addition of Li2CO3 with accelerated sintering schedule produced the theoretical density of CaZr4(PO4)6 and further addition of Li2CO3 rapidly decreased the sintered density. Minimum bulk thermal expansion of negative 5×10−6 °C−1 was obtained with the addition of 5 wt.% Li2CO3. The thermal hysteresis effect was minimized at the composition of 2.5 wt.% Li2CO3. It was demonstrated that by changing the composition and sintering schedule, the theoretical density of CaZr4(PO4)6 could be reached through liquid phase sintering and the thermal expansion characteristics can be engineered as desired by controlling its composition and sintering schedule.