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 Co₂NiO ₄ 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. A combination of experiment and theory quantifies the dependence of the conductivity in Co₂ZnO₄ and Co₂NiO ₄ on the cation disorder. A self-doping mechanism is identified as the origin of conductivity and a thermodynamic model is used to describe the non-equilibrium cation disorder in terms of an effective temperature. The conductivity in spinels can be controlled by manipulating the cation disorder.