Rapid synthesis of low thermal expansion materials of Ca1−xSrxZr4P6O24

A rapid synthesis method is introduced for the synthesis of low thermal expansion materials of Ca1−xSrxZr4P6O24 (x = 0, 0.5 and 1) and optimum synthesizing conditions are obtained. It is shown that these materials can be synthesized by one-step sintering by putting the preheated mixture of CaCO3, SrCO3 and NH4H2PO4 directly into a pipe furnace at the sintering temperature (1673–1873 K). With this method, the sintering procedure is much simplified and sintering time and energy exhausts are considerably reduced with respect to the conventional solid state reactions which usually require multiple-step and longer time sintering at different temperatures with intermediate grindings for the synthesis of these materials. By putting the samples directly at the sintering temperature, the formation of the secondary phase ZrP2O7 can be largely avoided. This insures the rapid synthesis of Ca1−xSrxZr4P6O24. MgO is introduced to increase the density of Ca0.5Sr0.5Zr4P6O24 ceramics. A sintered density of 3.10 g cm−3, relative density of 96.2% for Ca0.5Sr0.5Zr4P6O24 is obtained with 1.0 wt.% MgO. The coefficients of thermal expansion are about 0.27 × 10−6 K−1. Raman spectroscopic and differential scanning calorimetry (DSC) analyses reveal that there are no phase transitions of all the samples from 113 K to 1423 K.