Shear transformation to produce a new phase of polymeric sulfur nitride (SN)x

Abstract

The solid-state synthesis of a new phase of (SN)x is reported. X-ray diffraction results show that mechanical shear induces a transformation of the known, monoclinic phase (space group P21/c) to a phase of orthorhombic symmetry(probable space group P212121). The unit cell parameters of the shear-induced phase of (SN)x are a=6.251, b=4.429, and c=4.807 Å. Since the approximate chain repeat dimension (b) and the chain symmetry (21) are the same before and after the transformation, the chain geometries for the two phases of (SN)x are predicted to be quite similar, if not identical. However, important differences are expected for interchain interactions that have been previously shown to be essential in understanding various properties of the monoclinic phase of (SN)x. Both phases of (SN)x are shown to be stable with respect to thermally-induced interconversion for temperatures up to 175°C. Molecular packing calculations are used to predict structural aspects of the shear-induced phase and the relationship between parent and daughter phases. The latter results are consistent with the monoclinic-to-orthorhombic transformation being martensitic in character.