Hopping versus bulk conductivity in transparent oxides: 12CaO.7Al2O3

TL;DR

This study uses first-principles calculations to elucidate the high conductivity mechanism in mayenite-based oxides, showing a transition from hopping to bulk conduction due to Coulomb blockade elimination, and clarifying the electronic nature of the material.

Contribution

It provides a detailed electronic and optical comparison revealing the conduction mechanism and clarifying that the material is not an electride, unlike previous suggestions.

Findings

High conductivity achieved by eliminating Coulomb blockade.

Transition from variable range hopping to bulk conductivity.

Material exhibits significant electron delocalization, not an electride.

Abstract

First-principles calculations of the mayenite-based oxide, [Ca12Al14O32]{2+}(2e-), reveal the mechanism responsible for its high conductivity. A detailed comparison of the electronic and optical properties of this material with those of the recently discovered novel transparent conducting oxide, H-doped UV-activated Ca12Al14O33, allowed us to conclude that the enhanced conductivity in [Ca12Al14O32]{2+}(2e-) is achieved by elimination of the Coulomb blocade of the charge carriers. This results in a transition from variable range hopping behavior with a Coulomb gap in H-doped UV-irradiated Ca12Al14O33 to bulk conductivity in [Ca12Al14O32]{2+}(2e-). Further, the high degree of the delocalization of the conduction electrons obtained in [Ca12Al14O32]{2+}(2e-) indicate that it cannot be classified as an electride, originally suggested.