STRUCTURAL AND TRANSPORT-PROPERTIES OF THE ZN1-XCUXAL2O4 AND GA1-XFEXNICOO4 SYSTEMS

This paper presents experimental data on the electrical conductivity, thermoelectric coefficient, infrared absorption and reflectance spectra and X-ray diffraction measurements of (a) Znl xCuxA12O4 and (b) Ga1 _xFexNiCoO4 systems. It is found that the activation energy of the conductivity decreases with increasing Cu2 + concentration in system (a) and with Fe3 + content in the crystal lattice of system (b). The thermoelectric coefficient data for systems (a) and (b) also decrease with increasing Cu2+ and Fe3+ concentrations. Thus the observed changes in conductivity and thermoelectric coefficient could be described in terms of transport and structural properties. X-ray analysis revealed that all the compounds of systems (a) and (b) crystallized in single-phase cubic structures. The reflectance spectra of all the compounds of system (a) indicated the presence of Cu2+ in tetrahedral and octahedral sites. All the compounds of system (b) and compounds with x≤0 2 of system (a) exhibited p-type semiconductivity which could be ascribed to the transfer of cations from octahedral (B) to tetrahedral (A) sites, thereby creating holes. However, the compounds having 0 4 ≤ x ≤ l of system (a) exhibited n-type semiconductivity due to Cu2+ and Cu+ pair formation. © 1990 Taylor & Francis Ltd.