Formation of highly oriented large nanoscale In2Te3 precipitates in bulk Bi2Te3

Nucleation and growth precipitation experiments were conducted on samples of In-alloyed Bi2Te3 with a starting composition of Bi1.65In0.35Te3 (7 at.% In) to investigate the phase diagram of the Bi2Te3–In2Te3 system. Temperature-dependent equilibrium solubilities were determined at 500 and 450 °C and also the maximum solubility of In in Bi2Te3 was verified by unidirectional solidification using the Bridgman method. The In2Te3 structures formed during precipitation are either plates or elongated ribbons with thicknesses of the order of hundreds of nanometers with a heavily temperature-dependent spacing distribution. All in-grain precipitation occurs along the {0 0 0 1} family of planes in Bi2Te3. The orientation relationship between Bi2Te3–In2Te3 was found to be {0 0 0 1}Bi2Te3 ∥ {1 1 1}In2Te3 and consequently 〈112¯0〉 Bi2Te3 ∥ 〈1 1 0〉 In2Te3, which aligns the close-packed planes and directions. The resulting matrix is expected to be lightly doped and may be suitable for microstructure engineering for near room temperature thermoelectric applications.