The crystal structure and thermal expansion of Mo5SiB2

Mo5SiB2 (T2), synthesized with 11B, was studied using high temperature neutron powder diffraction. This ternary compound crystallizes with a tetragonal unit cell, space group I4/mcm, with room temperature lattice parameters a=6.0272(3) and c=11.0671(7) Å. The structural refinement reveals that B substitutes for a minor amount of Si for a formula of Mo5Si0.89B2.11. The refined lattice parameters studied as a function of temperature give average thermal expansion coefficients along the a and c-axes, (7.9±0.1)×10−6 K−1 and (7.5±0.2)×10−6 K−1, respectively. The thermal expansion of Mo5SiB2 is, therefore, nearly isotropic. A more detailed evaluation shows that the thermal expansion coefficient, as well as the thermal expansion anisotropy, vary with temperature.