Role of atomistic structure in the stochastic nature of conductivity in substoichiometric tantalum pentoxide

First-principles calculations of electrical conductivity (sigma(o)) are revisited to determine the atomistic origin of its stochasticity in a distribution generated from sampling 14 ab-initio molecular dynamics configurations from 10 independently quenched models (n = 140) of substoichiometric amorphous Ta2O5, where each structure contains a neutral O monovacancy (V-O(0)). Structural analysis revealed a distinct minimum Ta-Ta separation (dimer/trimer) corresponding to each V-O(0) location. Bader charge decomposition using a commonality analysis approach based on the sigma(o) distribution extremes revealed nanostructural signatures indicating that both the magnitude and distribution of cationic charge on the Ta subnetwork have a profound influence on sigma(o). Furthermore, visualization of local defect structures and their electron densities reinforces these conclusions and suggests sigma(o) in the amorphous oxide is best suppressed by a highly charged, compact Ta cation shell that effectively screens and minimizes localized V-O(0) interaction with the a-Ta2O5 network; conversely, delocalization of V-O(0) corresponds to metallic character and high sigma(o). The random network of a-Ta2O5 provides countless variations of an ionic configuration scaffold in which small perturbations affect the electronic charge distribution and result in a fixed-stoichiometry distribution of sigma(o); consequently, precisely controlled and highly repeatable oxide fabrication processes are likely paramount for advancement of resistive memory technologies. (C) 2016 AIP Publishing LLC.