Resistivity, thermopower and the correlation to infrared active vibrations of Mn1.56Co0.96Ni0.48O4 spinel films sputtered in an oxygen partial pressure series

Abstract

Mn 1.56 Co 0.96 Ni 0.48 O 4 spinel was sputter deposited using a series of oxygen partial pressures. Electrical resistivity versus temperature and thermopower versus temperature measurements at each oxygen partial pressure were made. The variations of the thermopower and resistivity with oxygen partial pressure are consistent with a change in the ratio of Mn3+to Mn4+ cations, which occurs due to changes of oxygen content of the material. The weak temperature dependence of the thermopower indicates small polaron hopping is the charge transport mechanism. Combining the models of Mott and Schnakenberg to analyze the transport data, we find that the Debye temperature (or frequency) is an increasing function of the oxygen partial pressure used during sputtering. The calculated shift in the Debye frequency from the resistivity is consistent with the observed shift in the fundamental infrared active lattice vibrations from Fourier transform infrared spectroscopy and Raman spectroscopy.