Neutron powder diffraction study of the crystal structures of ZrAu

Abstract

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 ̄ , a=11.537(8) Å, b=4.841(1) Å, c=11.507(7) Å, α=87.42(1)°, β=104.82(1)° and γ=92.41(2)° 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) Å, b=4.828(3) Å, c=11.719(18) Å, β=107.090(17)° 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) Å and c=3.416(3) Å).