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

Mn1.56Co0.96Ni0.48O4 spinel was sputter deposited using a series of oxygen partial pressures. Electrical resistivity versus temperature and thermopowe r versus temperature measurements at each oxygen partial pressure were made . The variations of the thermopower and resistivity with oxygen partial pre ssure are consistent with a change in the ratio of Mn(3+)to Mn4+ cations, w hich occurs due to changes of oxygen content of the material. The weak temp erature dependence of the thermopower indicates small polaron hopping is th e charge transport mechanism. Combining the models of Mott and Schnakenberg to analyze the transport data, we find that the Debye temperature (or freq uency) is an increasing function of the oxygen partial pressure used during sputtering. The calculated shift in the Debye frequency from the resistivi ty is consistent with the observed shift in the fundamental infrared active lattice vibrations from Fourier transform infrared spectroscopy and Raman spectroscopy. (C) 1999 American Institute of Physics. [S0021-8979(99)04913- 0].