A tunable conductivity has been achieved by controllable substitution of an ultraviolet 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.
M. I. Bertoni et al., "Tunable Conductivity and Conduction Mechanism in an Ultraviolet Light Activated Electronic Conductor," Journal of Applied Physics, American Institute of Physics (AIP), Jan 2005.
The definitive version is available at http://dx.doi.org/10.1063/1.1899246
National Science Foundation (U.S.)
United States. Department of Energy
Keywords and Phrases
Seebeck Effect; Calcium Compounds; Conducting Materials; Decomposition; Density Functional Theory; Hydrogen; Magnesium Compounds; Optical Constants; Small Polaron Conduction; Transparency
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