Structure and physical properties of YCo O3 at temperatures up to 1000 K

Knížek, K. , Jirák, Z. , Hejtmánek, J. , Veverka, M. , Maryško, M. , Hauback, B.C. , Fjellvåg, H.
Physical review B, Vol. 73, no. 21 (2006), 214443
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The crystal structure of perovskite YCo O3 has been studied by neutron powder diffraction up to high temperatures. The orthorhombic Pbnm symmetry is confirmed in the whole temperature range. A significant isotropic enlargement of Co O6 octahedra is evidenced above 600 K leading to unit cell expansion and increased octahedral tilting. Supported by complementary physical measurements, the origin of anomalous expansion is identified with a gradual transition of Co3+ ions from the diamagnetic low-spin (S=0) ground state to excited magnetic states with spin S=1 or 2. The magnetic transition is closely followed by a broad resistivity transition of the insulator-metal type, centered at 750 K. The changes in magnetic susceptibility, electric resistivity, thermopower and thermal conductivity associated with transitions in YCo O3 are discussed in comparison with similar data on related perovskite LaCo O3. © 2006 The American Physical Society.
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