Anomalous Conductivity in the Rutile Structure Driven by Local Disorder.

Abstract

Many rutile-type materials are characterized by a softness in shear with pressure which is coupled to a Raman-active librational motion. Combining direct studies of anion positions in SnO2 with measurements of its electronic properties, we nd a cor- relation between O sublattice disorder between 5 - 10GPa and an anomalous decrease up to 4 orders of magnitude in electrical resistance. Hypotheses into the atomistic nature of the phenomenon are evaluated via ab initio calculations guided by EXAFS analysis, and the most likely mechanism is found to be the displacement of single an- ions resulting from the pressure-induced softening of the librational mode. Based on this mechanism, we propose that the same behavior should feature across all materials exhibiting a rutile to CaCl2 phase transition, and that conductivity in other rutile-type materials could be facilitated at ambient pressure by appropriate design of devices to enhance defects of this nature.