The orthorhombic structures (Pbnm-Di~; No. 62) of GeS, GeSe, SnS and SnSe have been refined (X-ray diffractometer data:

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The thermal expansion of GeSe has been studied above room temperature up to the melting point of 670 ± 5°C by X‐ray diffraction techniques using a 190 mm Unicam high temperature camera. The thermal expansion of the crystallographic axes is linear with a distinct change of the expansion coeffients for all axes above 400°C. The relative changes of the axes indicate a rearrangement of the structure towards cubic symmetry with increasing temperature. The transformation of GeSe from the orthorhombic to a normal NaCl‐type structure is observed at 651 ± 5°C. The lattice parameter of the cubic form of GeSe is a0 = 5.730 ± 0.003 Å at 656°C. The GeSe lattice remains cubic up to the melting point.

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The thermal expansion of GeS has been studied above room temperature up to the melting point of 658 ± 5°C by X‐ray diffraction techniques using a 190 mm diameter Unicam high temperature camera. The thermal expansion of the crystallographic axes is linear with distinct changes in the rate of expansion at about 250°C, 370°C and 510°C. No first‐order structural transformation was observed for this system up to the melting point. The results of additional studies on GeTe are in general agreement with those of others and confirm trends in the thermal expansion behavior of the germanium monochalcogenide series.