Lattice thermal expansion of the solid solutions (La1 − xSmx)2Ce2O7

A series of solid solutions with the general formula (La1 − xSmx)2Ce2O7 (0.0 ≤ x ≤ 1.0) were prepared by the coprecipitation–calcination method. The products obtained were characterized by powder X-ray diffraction for phase purity. It was observed that La3+ and Sm3+ can form complete solid solution in (La,Sm)2Ce2O7 with defect-fluorite-type phase. The unit cell parameters of these solutions were calculated by a least squares method and the lattice parameters decreased linearly as x increased. The lattice thermal expansion behavior of (La1 − xSmx)2Ce2O7 (0.0 ≤ x ≤ 1.0) was investigated by high-temperature X-ray diffraction in the temperature range 298–1623 K. The lattice parameters aT of all the solutions at different temperature can be expressed as aT = a + bT + cT2. As x < 1, the thermal expansion has a sudden decrease at ca. 473 K. The coefficients of lattice thermal expansion of Sm2Ce2O7 were 10.2–13.6 × 10−6 K−1 from 298 to 1623 K, and without the thermal contraction at low temperature. The materials show positive or negative thermal expansion due to the asymmetric anharmonic vibration.