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 _1.65In _0.35Te 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 〈112̄0〉 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.