Neutron powder diffraction study of the crystal structures of ZrAu

The crystal structures and structure transformations of ZrAu have been investigated by means of neutron powder diffraction on as-cast ingots placed in evacuated quartz tubes to avoid oxidation. In the temperature range 300-1273 K, two structure transformations have been observed and confirmed by resistivity measurement results. The first one occurs at about 670 K and is a second-order transition as it does not yield any differential thermal analysis (DTA) event. The second one occurs at 840 K as previously reported. In each temperature interval, a complete structure model compatible with collected data was derived and used for Rietveld analysis. Between room temperature and 670 K, the structure is found triclinic (P (1) over bar, a = 11.537(8) Angstrom, b = 4.841 (1) Angstrom, c = 11.507(7) Angstrom, alpha = 87.42(1)degrees, beta = 104.82(1)degrees and gamma = 92.41(2)degrees at 300 K). Above 670 K and below 840 K, the structure is satisfactorily described in the monoclinic space group P2/m (a = 11.695 (16) Angstrom, b = 4.828(3) Angstrom, c = 11.719(18) Angstrom, beta = 107.090(17)degrees at 773 K) and finally between 840 and 1273 K, it is tetragonal, closely related to the A2-type structure (P4/mmm, a = 4.835 (2) Angstrom and c = 3.416(3) Angstrom). (C) 2003 Elsevier B.V. All rights reserved.