Pekinchak O. Modification of the structure and properties of functional materials based on cobaltites RCoO3 (R = Pr-Tb)

This work is devoted to the study of the influence of cation substitution on the crystal structure parameters, deformation of perovskite structure, thermal expansion, spin-spin and metal-insulator phase transitions in the mixed cobaltites-ferrites RCo1 xFexO3 (R = Pr, Nd, Sm, Eu, Gd, Tb), potential functional materials for diverse applications. Phase and structural behaviour in the RCoO3 RFeO3 pseudobinary system has been investigated in a whole concentration range in the temperature range 298-1173 K. Formation of a continuous solid solution RCo1 xFexO3 with orthorhombic perovskite structure (GdFeO3 type of structure, space group Pbnm) has been revealed. Crystal structure parameters of new mixed praseodymium cobaltites-ferrites RCo1xFexO3 has been determined in the temperature range of 298-1173 K by means of in situ high-resolution X-ray synchrotron powder diffraction. Pronounced anomalies in the lattice expansion, as well as in other structural parameters, such as interatomic distances and atomic displacement parameters, has been detected. It was shown that these anomalies are associated with partial transitions of Co3+ ions to the higher spin states and metal-insulator transitions occurred in corresponding systems. The influence of cation substitution on the structural and thermal parameters of the RCoO3-RFeO3 system has been established. It was shown, that partial substitution of iron for the cobalt sites in RCo1 xFexO3 series led to increase of perovskite structure deformation and to the increasing temperatures of spin-spin and insulator-metal transitions.