Preparation and structural study of sodium germanium phosphate-sodium titanium phosphate solid solutions II.- Evolution of thermal expansion with composition

Abstract

Low thermal expansion materials from solid solutions NaGe 2−xTi x(PO 4) 3 (x = 0.25, 0.5, 0.8, 1) with NZP structure have been obtained by solid state reaction. Lattice thermal expansion coefficients have been determined from x-ray diffraction data at temperatures ranging from 26 to 800°C. Evolution of the thermal expansion with composition has been studied. The thermal expansion coefficient in the a direction decreases from 1.348 × 10 −5° C −1 to 0.8340 × 10 −5° C t-1 and the thermal expansion coefficient in the c direction increases from 1.244 × 10 −5° C −1 to 1.743 × 10 −5° C −1 with increasing x, with a deflection in the composition with x = 0.5. Evolution of macroscopic thermal expansion with composition has been studied by dilatometry measurements. DSC measurements have been also carried out on these samples. Composition with x = 1, NaGeTi(PO 4) 3, shows a different thermal behavior from those of the other solid solutions with higher Ge content, which present an isotropic thermal expansion as germanium compound does.