PREPARATION AND STRUCTURAL STUDY OF SODIUM GERMANIUM PHOSPHATE-SODIUMTITANIUM PHOSPHATE SOLID-SOLUTIONS .2. EVOLUTION OF THERMAL-EXPANSIONWITH COMPOSITION

Low thermal expansion materials from solid solutions NaGe2-xTix(PO4)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 dete rmined from x-ray diffraction data at temperatures ranging from 26 to 800-degrees-C. Evolution of the thermal expansion with composition has been studied. The thermal expansion coefficient in the a direction de creases from 1.348 x 10(-5)degrees-C-1 to 0.8340 x 10(-5)degrees-C-1 a nd the thermal expansion coefficient in the c direction increases from 1.244 x 10(-5)degrees-C-1 to 1.743 x 10(-5)degrees-C-1 with increasin g x, with a deflection in the composition with x = 0.5. Evolution of m acroscopic thermal expansion with composition has been studied by dila tometry measurements. DSC measurements have been also carried out on t hese samples. Composition with x = 1, NaGeTi(PO4)3, shows a different thermal behavior from those of the other solid solutions with higher G e content, which present an isotropic thermal expansion as germanium c ompound does.