Mercury thioarsenate glasses: a hybrid chain/pyramidal network

Abstract

Very little is known about mercury chalcogenide glasses. Using Raman spectroscopy and DFT modelling, we show that the (HgS)_x(As₂S₃)_1−x glasses, 0.0 ≤ x ≤ 0.5, form a hybrid Hg–S chain/As–S pyramidal network, highly unusual for metal chalcogenide glasses. This network is evidenced by Hg–S stretching modes at 300 and 370 cm⁻¹ and an As–S spectral envelope centred at 340 cm⁻¹. The decreasing glass transition temperature is consistent with a gradual substitution of more rigid corner-sharing CS-AsS_3/2 pyramids by flexible (HgS_2/2)_n chain fragments. Nevertheless we cannot exclude completely the presence of a small fraction of HgS_4/4 tetrahedral units. A non-monotonic change in electronic transport properties and metacinnabar β-HgS traces detected using neutron diffraction in large x = 0.5 samples support the dual structural role of mercury.