Document Type : Original Article
Authors
1
Institute of Solid State Physics, University of Latvia, 8 Kengaraga street, LV1063, Riga, Latvia
2
Institute of Nanoscience and Nanotechnology, Kafrelsheikh University, 33516 Kafr el-shiekh, Egypt
3
Facultate de Ciencias, Sau Paulo State University, Bauru, Brasil
4
Institute of Theoretical Chemistry, University of Stuttgart, Molpro Quantum Chemistry Software, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
5
ACCADEMIA DELLE SCIENZE DI TORINO,Via Accademia delle Scienze 6, 10123 Torino, (To), Italy
Abstract
Background: The electronic and geometrical properties of LaCoO3, which has a closed shell ground state (Sz=0), are compared with the ones of KCoF3, presenting a high spin (Sz=3/2) ground state. In an ideal fully ionic model, the Co occupancy in the two compounds is d6 (oxide) and d7 (fluoride).
Methods: The analysis of the density of states and of the charge distribution, the latter through a Mulliken analysis, shows that in the oxide the partially covalent character of the Co-O bonds deeply alters the ideal picture, and that not only the t2g, but also the eg subshell is occupied, with an overall d occupancy close to 7 electrons (one electron in the eg subshell), very close to the fluoride occupancy.
Results and conclusion: The deformation with respect to the cubic aristotype (SG 221), down to the tetragonal (SG 123, 127 and 140), orthorhombic (SG 62) and rhombohedral (SG 167) symmetry, with a corresponding increase of the inner degrees of freedom (from 1 to 10) and size of the unit cell (from 5 to 20 atoms), is explored, which confirms that the octahedra remain essentially regular, with an energy gain along the full group-subgroup chain of only 4.6 mEh (0.125 eV) per formula unit. In spite of the similar total occupancy of the d shell, the electronic configuration of Co in KCoF3 is quite different, with a high spin (, with 5α and 2β electrons) ground state.
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