Synthesis, microstructure and thermal expansion studies on Ca_0·5+x/2Sr_0·5+x/2Zr₄P_6−2x Si_2x O₂₄ system prepared by co-precipitation method

Abstract

We report on the synthesis, microstructure and thermal expansion studies on Ca_{0·5 + x/2}Sr_{0·5 + x/2}Zr₄P_6 − 2x Si_2x O₂₄ (x = 0·00 to 1·00) system which belongs to NZP family of low thermal expansion ceramics. The ceramics synthesized by co-precipitation method at lower calcination and the sintering temperatures were in pure NZP phase up to x = 0·37. For x ≥ 0·5, in addition to NZP phase, ZrSiO₄ and Ca₂P₂O₇ form as secondary phases after sintering. The bulk thermal expansion behaviour of the members of this system was studied from 30 to 850 °C. The thermal expansion coefficient increases from a negative value to a positive value with the silicon substitution in place of phosphorous and a near zero thermal expansion was observed at x = 0·75. The amount of hysteresis between heating and cooling curves increases progressively from x = 0·00 to 0·37 and then decreases for x > 0·37. The results were analysed on the basis of formation of the silicon based glassy phase and increase in thermal expansion anisotropy with silicon substitution.