Mechanical Properties of Thermoelectric Ba8Al15Si31 Clathrate Prepared by Combining Arc Melting and Spark Plasma Sintering Techniques

Abstract

The mechanical properties (the elastic moduli, hardness, and fracture toughness) were investigated for polycrystalline Ba8Al15Si31 clathrate as one of useful thermoelectric materials on a phonon glass and electron crystal concept. Samples were prepared by combining arc melting and spark plasma sintering techniques. The Young’s modulus E = 96.88 GPa, shear modulus G = 38.61 GPa, bulk modulus K = 65.77 GPa, and Poisson’s ratio ν = 0.2545 were calculated from longitudinal sound velocity vL = 6105 m/s and transverse sound velocity vT = 3503 m/s, measured by an ultrasonic test. The elastic constants c11 = 78.64 GPa, c12 = 40.03 GPa, and c44 = 38.61 GPa were calculated from E and G. The Vickers hardness HV and Young’s modulus E were simultaneously determined to be 634 and 109.7 GPa, respectively, by a nanoindentation test. The fracture toughness KIC was determined to be 1.1 MPa m1/2, which was comparable to typical values 1.1–1.2 MPa m1/2 for thermoelectric silicide Mg2Si, by a Vickers indentation fracture test.