Abstract

A single crystal of natural berthierite, FeSb2S4, was investigated at high pressure by means of X-ray diffraction using a diamond-anvil cell equipped with diamond backing plates. No phase transitions were indicated up to 8 GPa. The third-order Birch–Murnaghan equation of state, calculated using high-accuracy volume–pressure data up to 8.05 GPa, gave the following coefficients: V0 = 608.78(7) Å3, KT0 = 37.2(2) GPa and K′ = 7.0(1). The evolution of the structure as a function of pressure has been determined at seven different pressures up to 7.41 GPa. As in other structures with stereochemically active lone-electron pairs (LEP), the Sb3+ LEP, influencing long Sb–S bonds in berthierite, accommodate most of the compression. The Fe octahedron, which is the stiffest coordination polyhedron in berthierite, increases its distortion until approximately 5 GPa, but shows pronounced stiffening at higher pressures. This deformation at high pressures can be related to an increase in the Jahn–Teller effect on the Fe2+ coordination. The influence of Fe on compressional behavior makes a distinct difference between the compression of berthierite and that of stibnite, Sb2S3. The bridging Fe coordination between the structural rods in berthierite makes it stiffer. This, together with the direct structural relation to the analogous PbBi2S4, galenobismutite, makes the compressional characteristics of berthierite more akin to those of galenobismutite, despite quantitative differences in the stereochemical expression of the LEP of Sb3+ and Bi3+.

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