Compressive creep behavior of cast Bi₂Te₃

In thermoelectric devices, Bi₂Te₃ must be able to operate under high temperature gradients for very long times (years) without appreciable deformation, while being subjected to stresses created by internal thermal mismatch and external forces (e.g., vibrations). The deformation rate of cast, coarse-grained Bi₂Te₃ was measured under uniaxial compressive stresses from 2 to 16MPa at temperatures between 400 and 500°C. At all temperatures, a power-law behavior is observed, with a stress exponent n=3-6 and an activation energy of ~145kJ/mol. Significant differences in creep rates are observed in duplicate experiments, which may be due to anisotropic creep resistance in coarse-grained specimens. Bi₂Te₃ is brittle at 400 and 450°C but shows some compressive ductility at 500°C, indicating that hot forging may be possible.