Control of the Electrical Properties in Spinel Oxides by Manipulating the Cation Disorder

In this work, the impact of cation disorder on the electrical properties of biaxially textured Co2ZnO4 and Co2NiO4 thin films grown by pulsed laser deposition are investigated using a combination of experiment and theory. Resonant elastic X-ray diffraction along with conductivity measurements both before and after post-deposition annealing show that Co2ZnO4 and Co2NiO4 exhibit opposite changes of the conductivity with cation disorder, which can be traced back to their different ground-state atomic structures, being normal and inverse spinel, respectively. Electronic structure calculations identify a self-doping mechanism as the origin of conductivity. A novel thermodynamic model describes the non-equilibrium cation disorder in terms of an effective temperature. This work offers a way of controlling the conductivity in spinels in a quantitative manner by controlling the cation disorder and a new design principle whereby non-equilibrium growth can be used to create beneficial disorder.