Formation of highly oriented large nanoscale In_2Te_3 precipitates in bulk Bi_2Te_3

Nucleation and growth precipitation experiments were conducted on samples of In-alloyed Bi_2Te_3 with a starting composition of Bi_(1.65)In_(0.35)Te_(3) (7 at.% In) to investigate the phase diagram of the Bi_2Te_3–In_2Te_3 system. Temperature-dependent equilibrium solubilities were determined at 500 and 450 °C and also the maximum solubility of In in Bi_2Te_3 was verified by unidirectional solidification using the Bridgman method. The In_2Te_3 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 Bi_2Te_3. The orientation relationship between Bi_2Te_3–In_2Te_3 was found to be {0 0 0 1}Bi_2Te_3 || {1 1 1}In_2Te_3 and consequently 〈 1 1 2¯ 0 〉 Bi_2Te_3 || 〈1 1 0〉 In_2Te_3, 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.