Phase equilibria and thermal expansion of CaTiO 3 doped with neptunium

Abstract

Phase relationships between NpO 2 and CaTiO 3 or Ca(Ti,Al)O 3 were investigated by X-ray diffraction (XRD) analysis at room temperature, using specimens prepared at 1773 K in Ar–8%H 2 atmosphere. Single phase solid solutions were formed for 0–7.5 mol% Np doped CaTiO 3 and 1–10 mol% Np doped Ca(Ti,Al)O 3. By substituting Al for Ti in CaTiO 3, Np solubility in Ca(Ti,Al)O 3 increased. Thermal expansions of (Ca 1− x Np x )TiO 3 ( x = 0.03, 0.05 and 0.075) were measured for temperatures between room temperature and 1273 K in Ar-8%H 2 atmosphere using high-temperature XRD technique. Volumetric thermal expansion coefficients of these three specimens were nearly the same value, suggesting that the incorporation of tetravalent Np into CaTiO 3 had practically no effect on stabilization of the crystal lattice.