Novel oxides with spin state instabilities for electronic and energy applications

Cobalt oxides present a plethora of very interesting properties like metal-insulator transitions, spin-state changes, giant magnetoresistance, double-exchange, phase separation, high thermoelectric power, oxygen diffusivity, mixed-conduction, charge and orbital ordering or superconductivity among others. These properties are interesting not only from a fundamental point of view but also due to their potential applicability in different fields. One very remarkable characteristic of many cobalt compounds is the ability of Co ions to adopt different spin states. This makes that Co oxides have, in comparison with other transition metal oxides, an extra degree of freedom: the spin state of Co. So, the investigation of novel cobaltites with different structures and prepared in different forms is between the most attractive opportunities within strongly correlated systems: the spin state of Co at selected sites in the structure plays a key role in the structural, magnetic, magnetotransport properties, electronic and ion mobility or the thermoelectric power. This research is inscribed inside the wider objective of understand and control the spin state and electronics degrees of freedom of Co cations, especially with 3+ valence. Trivalent cobalt oxides exhibit unique electronic phases characterized by the interplay between nearly degenerate spin states.