Thermal Conductivity in <I>X</I><SUB>2</SUB><I>YZ</I> Heusler Type Intermetallic Compounds

Abstract

Results are given of comprehensive measurements on thermal conductivity of Heusler type intermetallic compounds Fe2AlTi, Co2AlTi, Ni2AlTi, Ni2GaTi, Ni2AlZr and Ni2AlHf. The compounds have fully ordered L21 structure. There exists a wide single phase region of L21 in Ni–Al–Ti ternary alloy system. The contour map showing the magnitude of thermal conductivity is constructed in Ni2AlTi single phase region. The thermal conductivity in Ni2AlTi takes a maximum of 21.4 Wm−1K−1 at stoichiometry which is much lower than that of NiAl having a B2 structure. By the deviation from stoichiometry, the thermal conductivity decreases in Heusler compounds. The magnitude of thermal conductivity in Fe2AlTi, Co2AlTi and Ni2AlTi are compared in connection with those of B2 aluminides (FeAl, CoAl, NiAl) and titanides (FeTi, CoTi, NiTi). Thermal conductivities in three kinds of Heusler compounds X2AlTi (X: Fe, Co, Ni) are almost the same value of approximately 20 Wm−1K−1. Ordering from B2 to L21 incrcases thermal conductivity in accord with the estimation by Nordheim relation. The magnitude of thermal conductivity in X2YZ Heusler compounds, including Ni2GaTi, Ni2AlZr and Ni2AlHf, is related to those of XY and XZ compounds having a B2 structure.