Synthesis and thermal expansion behavior of liquid phase sintered CaZr_4(PO_4)_6―Li_2O

摘要

Lithium oxide was introduced into the CaZr_4(PO_4)_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 Li_2O 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 Li_2CO_3 with accelerated sintering schedule produced the theoretical density of CaZr_4(PO_4)_6 and further addition of Li_2CO_3 rapidly decreased the sintered density. Minimum bulk thermal expansion of negative 5 x 10~(―6) ℃~(―1) was obtained with the addition of 5 wt.% Li_2CO_3. The thermal hysteresis effect was minimized at the composition of 2.5 wt.% Li_2CO_3. It was demonstrated that by changing the composition and sintering schedule, the theoretical density of CaZr_4(PO_4)_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.