Synthesis, sintering and thermal expansion of Ca1-xSrxZr4P6O24 : an ultra-low thermal expansion ceramic system

Ca1-xSrxZr4P6O24 system which belongs to a new large family of low thermal expansion materials known as NZP or CTP, was synthesised by solid state and sol-gel methods. The conventional sol-gel method was modified by introducing a seeding step which significantly improved the sintering characteristics and the microstructure of the sintered material. Sintering data were compared with those obtained by powder mixing. Thermal expansion of the sintered samples was measured by classical dilatometry and by high-temperature X-ray diffractometry. CaZr4P6O24 and SrZr4P6O24 phases had opposite anisotropies in their respective axial thermal expansions, leading to the development of a crystalline solution composition of nearly zero expansion. Microstructures of the sintered specimens were examined by SEM. 18 refs.