The crystal structure and thermal expansion of Mo5SiB2

Mo5SiB2 (T2). synthesized with B-11, was studied using high temperature neu tron powder diffraction. This ternary compound crystallizes with a tetragon al unit cell. space group 14/mcm. with room temperature lattice parameters a = 6.0271(3) c = 11.0671(7) Angstrom. The structural refinement reveals th at 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 av erage thermal expansion coefficients along the a and c-axes, (7.9 +/-0.1)x1 0-(6) K-1 and (7.5+/-0.2)x10(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 an isotropy, vary with temperature. Published by Elsevier Science Ltd. All rig hts reserved.