2018 Volume 126 Issue 10 Pages 743-749
The phase transition of Sm3NbO7 with orthorhombic fluorite-related structure was investigated. Three kinds of solid solutions, Sm3(Nb1−xTax)O7, (Sm1−xNdx)3NbO7, and (Sm1−xEux)3NbO7 were prepared. Sm3NbO7 and Sm3TaO7 form complete solid solutions, and their structures are well described with the space group C2221. The phase transition temperature for Sm3(Nb1−xTax)O7 increases from 1080 K with increasing Ta concentration. Sm3TaO7 undergoes the phase transition when the temperature is increased through ca. 1340 K and above the transition temperature, its structure is well described with space group Pnma. The phase transition temperature for (Sm1−xNdx)3NbO7 decreases with Nd concentration. On the other hand, that for (Sm1−xEux)3NbO7 increases with the ratio of Eu concentration. However, both of these solid solutions show the same trend, i.e., with decreasing the average rare earth size, the phase transition temperature of (Sm1−xLnx)3NbO7 (Ln = Nd, Eu) increases. This trend is the same as that for Ln3MO7 (M = Mo, Ru, Re, Os, or Ir). That is, the phase transition occurs with lattice contraction.