Phase equilibria and thermal expansion of CaTiO3 doped with neptunium

Phase relationships between NpO2 and CaTiO3 or Ca(Ti,Al)O3 were investigated by X-ray diffraction (XRD) analysis at room temperature, using specimens prepared at 1773 K in Ar–8%H2 atmosphere. Single phase solid solutions were formed for 0–7.5 mol% Np doped CaTiO3 and 1–10 mol% Np doped Ca(Ti,Al)O3. By substituting Al for Ti in CaTiO3, Np solubility in Ca(Ti,Al)O3 increased. Thermal expansions of (Ca1−xNpx)TiO3 (x = 0.03, 0.05 and 0.075) were measured for temperatures between room temperature and 1273 K in Ar-8%H2 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 CaTiO3 had practically no effect on stabilization of the crystal lattice.