Structure, electrical conducting and thermal expansion properties of Ln0.6Sr0.4Co0.2Fe0.8O3 (Ln = La, Pr, Nd, Sm) perovskite-type complex oxides

Fine and uniform Ln0.6Sr0.4Co0.2Fe0.8O3 (Ln = La, Pr, Nd, Sm) powders with a perovskite phase were produced using a glycine–nitrate process. The structure, electrical conducting and thermal expansion properties of the resulting ceramics were investigated. The results indicate that replacing La3+ by smaller lanthanide cations led to a change in crystal structure from rhombohedral to orthorhombic symmetry and a decrease of the pseudo-cubic lattice constant. It was found that the electrical conducting properties decrease with reducing lanthanide cation size. Compared with La0.6Sr0.4Co0.2Fe0.8O3, the degradation of the electrical conducting properties in Pr0.6Sr0.4Co0.2Fe0.8O3 and Nd0.6Sr0.4Co0.2Fe0.8O3 is not pronounced, whereas the electrical conducting properties of Sm0.6Sr0.4Co0.2Fe0.8O3 decline to an unsatisfactory level. There is an evident increase in thermal expansion at high temperatures for all the compositions. This is attributed to a chemically induced lattice expansion due to oxygen lose and formation of oxygen vacancies. Pr0.6Sr0.4Co0.2Fe0.8O3 and Nd0.6Sr0.4Co0.2Fe0.8O3 present relatively low thermal expansion coefficient values of 14.2 × 10−6 and 13.2 × 10−6 K−1 averaged between 100–750 and 100–700 °C, respectively.