Transition of p- to n-Type Conductivity in Mechanically Activated Bismuth Telluride

Bismuth telluride (Bi2Te3) exhibits a transition from p- to n-type conduction as a result of high-energy ball milling The transition is monitored over mechanical activation through measurement of the thermoelectric properties in the temperature range of 1.9 K to 390 K. Data show a flip in polarity of the Seebeck coefficient from 225 mu V K-1 for the bulk sample to - 120 mu V K-1 (at 315 K) that correlates to fracturing the layered-like structure of stoichiometric Bi2Te3 into platelets and fine particles. The electronic transition is generated by fracturing the crystal 90 degrees to the basal plane. This is the structural equivalent to inducing n-type, anti-site defects on grain boundaries. The observed phenomenon could be exploited to fabricate p- and n-type legs for thermoelectric devices from the same material. In this report, we demonstrate that the value of the Seebeck coefficient for bismuth telluride can be tuned using mechanical treatment. We also determine how mechanical activation of Bi2Te3 impacts physical properties of the system, including: particle size, crystal structure, band gap, electrical and thermal conductivity, carrier concentration and mobility, average hopping distance, and the concentration of localized charged centers.