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

摘要

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 m = 0.2545 were calculated from longitudinal sound velocity v(L) = 6105 m/s and transverse sound velocity v(T) = 3503 m/s, measured by an ultrasonic test. The elastic constants c(11) = 78.64 GPa, c(12) = 40.03 GPa, and c(44) = 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 K-IC was determined to be 1.1 MPa m(1/2), which was comparable to typical values 1.1-1.2 MPa m(1/2) for thermoelectric silicide Mg2Si, by a Vickers indentation fracture test.