New low thermal expansion ceramics: Sintering and thermal behavior of Ln(1/3)Zr(2)(PO4)(3)-based composites

Materials with the general formula MxZr2(PO4)(3) are known to possess low coefficients of thermal expansion (CTE). The present work investigates the thermal properties of new composite materials issued from the decomposition at high temperature of Ln(1/3)Zr(2)(PO4)(3) (Ln=La, Gd). The decomposition process was studied and showed that the resulting powder was a LnPO(4), Zr2P2O9 and ZrO2 mixture. Composite materials made of that mixture were sintered and characterized. The effect of sintering aids such as ZnO was considered. Final densities of the composites were about 90% of theoretical density and these materials presented low CTE in the 10(-6)degrees C-1 range.