Abstract. The change in structure of glassy GeS₂ with pressure increasing to at ambient temperature was explored by using in situ neutron and x-ray diffraction. Under ambient conditions, the glass structure is made from a mixture of corner- and edge-sharing Ge(S_1/2)₄ tetrahedra where 47(5)% of the Ge atoms are involved in edge-sharing configurations. The network formed by these tetrahedra orders on an intermediate range as manifested by the appearance of a pronounced first sharp diffraction peak in the measured total structure factors at a scattering vector k = 1.02(2) Å⁻¹ which has a large contribution from Ge–Ge correlations. The intermediate range order breaks down when the pressure on the glass increases above 2 GPa but there does not appear to be a significant alteration of the Ge–S coordination number or corresponding bond length with increasing density. The results for the glass are consistent with a densification mechanism in which there is a replacement of edge-sharing by corner-sharing Ge centred tetrahedral motifs and/or a reduction in the Ge––Ge bond angle between corner-sharing tetrahedral motifs with increasing pressure. The change in structure with increasing temperature at a pressure of was also investigated by means of in situ x-ray diffraction as the glass crystallized and then liquefied. At 5.2(1) GPa and 828(50) K the system forms a tetragonal crystal, with space group and cell parameters a = b = 4.97704(12) and c = 9.5355(4) Å, wherein corner-sharing Ge(S_1/2)₄ tetrahedra pack to form a dense three-dimensional network. A method is described for correcting x-ray diffraction data taken in situ under high pressure, high temperature conditions for a cylindrical sample, container and gasket geometry with a parallel incident beam and with a scattered beam that is defined using an oscillating radial collimator. A method is also outlined for obtaining coordination numbers from direct integration of the peaks in measured x-ray total pair distribution functions.

Print publication: Issue 47 (25 November 2009)
Received 17 April 2009, in final form 4 August 2009
Published 5 November 2009