Paper TF1-ThA7
Controlling the Doping Concentration and Thermoelectric Applications of NaxV2O5 Thin Films

Thursday, October 18, 2007, 4:00 pm, Room 602/603

A high thermoelectric coefficient has been reported for Na_xV₂O₅ thin films. Na_xV₂O₅ structure consists of V₂O₅ layers, where Na atoms are retained between the layers, leading to various phases depending on the Na concentration. From the view point of processing this class of material for thermoelectric device applications, the precise control of the Na concentration and stabilization of the desired phase are the key issues. Recently, we presented a possibility of a solution route to make Na_xV₂O₅ thin films. Here, we report that through this new processing route, we can control the crystal phase of Na_xV₂O₅ thin films, specifically between β- and γ- phases, through annealing conditions and the choice of the substrates. β- phase is preferred for thermoelectric applications due to high Seebeck coefficient and a relatively good electrical conductivity. We found that on quartz substrate, high temperature annealing (600 C) leads to predominantly β- phase. By using soda-lime glass, which contains high Na₂O, as a substrate, the Na concentration in Na_xV₂O₅ films increases with increasing annealing time: coexistence of β- and γ- phases (10 minutes annealing) develops into γ- phases dominated film upon annealing for >30 minutes. Our results suggest that the Na concentration can be kinetically controlled in this material system. The possibility of Na_xV₂O₅- based thermoelectric device is proposed.