PNNL

Abstract

Mixed transition metal oxide spinels exhibit high electrical conductivity and enhanced infrared transmissivity resulting from the presence of small polarons in the lattice that are formed as a result of judicious choice of component metal cations and attendant resident cation charge states. Both substitution of lithium for cobalt while maintaining the spinel stoichiometry and controlled post deposition annealing were found to influence measured conductivity in both solution- and sputter-deposited thin films. For low lithium concentration, an improvement in conductivity was observed. However, higher lithium concentrations degraded conductivity. XPS and SIMS analyses of films with high lithium concentrations revealed an increased amount of lithium near the film surface resulting in adsorption of carbonate and subsequent formation of carbonyl and related species as seen in FTIR measurements. Results indicate that lithium additions to transition metal spinel oxides can lead to increased conductivity owing to polaron formation. However, high lithium additions favor lithium as interstitials where diffusion to the surface leads to formation of a passivating layer that degrades electrical conductivity.