Tunable Conductivity and Conduction Mechanism in a UV light activated electronic conductor

TL;DR

This study demonstrates how UV light activated electronic conductors with tunable conductivity can be achieved through Mg substitution in a transparent oxide, revealing insights into conduction mechanisms and material stability.

Contribution

It introduces a novel UV light activated conductor with controllable conductivity via Mg substitution and provides first principles insights into its conduction mechanism.

Findings

Conductivity decreases with Mg substitution from 0.26 to 0.106 S/cm.

Conductivity is reversible with temperature until decomposition.

Small polaron conduction suggested by temperature-independent Seebeck coefficient.

Abstract

A tunable conductivity has been achieved by controllable substitution of a novel UV light activated electronic conductor. The transparent conducting oxide system H-doped Ca12-xMgxAl14O33 (x = 0; 0.1; 0.3; 0.5; 0.8; 1.0) presents a conductivity that is strongly dependent on the substitution level and temperature. Four-point dc-conductivity decreases with x from 0.26 S/cm (x = 0) to 0.106 S/cm (x = 1) at room temperature. At each composition the conductivity increases (reversibly with temperature) until a decomposition temperature is reached; above this value, the conductivity drops dramatically due to hydrogen recombination and loss. The observed conductivity behavior is consistent with the predictions of our first principles density functional calculations for the Mg-substituted system with x=0, 1 and 2. The Seebeck coefficient is essentially composition- and temperature-independent, the later suggesting the existence of an activated mobility associated with small polaron conduction. The optical gap measured remains constant near 2.6 eV while transparency increases with the substitution level, concomitant with a decrease in carrier content.