Electrical and optical properties of Mn 1.56 Co 0.96 Ni 0.48 O4

Abstract

Mn<SUB>1.56</SUB>Co<SUB>0.96</SUB>Ni<SUB>0.48</SUB> is RF magnetron sputtered in a series of oxygen partial pressures, and non-stoichiometric films are produced. Conduction is small polaron hopping for all stoichiometries as evidenced by near temperature independent thermopower, and decreasing conduction activation energy with decreasing temperature. The carrier type transitions from p to n type with a decrease in the ratio of Mn<SUP>3+</SUP> to Mn<SUP>4+</SUP> concentration. The resistivity, and conduction activation energy are decreasing functions of the oxygen partial pressure. The Debye frequency increases with oxygen partial pressure as measured from the resistivity, and this is consistent with the observed shift of both the Raman and IR active lattice vibrations. The material has the spinel crystal structure, and as such is an optical window with the 3 phonon cutoff occurring at 17 micrometer. The material is transparent between 6 micrometer to 17 micrometer.