Balance between thermopower, electric and magnetic interactions in CuCrO2, Bi8Rh7O22 and MnSc2Se4

Transition metal based compounds with Ti, Cr, Mn, Fe, Co, and Ni are essential for many electronic functionalities. These compounds show rich physics with complex structural features that lead to interesting magnetic and electrical properties. Specific transition metal oxides reveal coupling between magnetic and electric order. This coupling requires a balance between crystal structure considerations and electronic interactions. In thermoelectric oxide materials, a balance must be found between the thermoelectric power factor, which is directly related to the Seebeck coefficient and the electrical conductivity, and the thermal conductivity. Finding this balance is facilitated in narrow band gap semiconductors, where the band gap can be modified by either intrinsic defects, extrinsic dopants or vacancies. This thesis covers both types of balance. The magnetic and thermoelectric properties are investigated in two p-type semiconductors, CuCrO2 and Bi8Rh7O22, and magneto-dielectric coupling is investigated in the A-site spinel, MnSc2Se4. CuCrO2 powder samples were synthesized using solid state reaction, sol-gel and hydrothermal methods, which provide different particle sizes. The morphology, grain interfaces and grain orientation have a more dominant effect on thermoelectric performance. The sol-gel synthesis is more promising by reducing the electrical resistivity, thus, increasing the thermoelectric properties. Furthermore, we study the pyroelectric current and the thermally stimulated depolarization of CuCrO2, which provides detailed information about the defect states of the compound