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Lanthanum disulphide, LaS2: is orthorhombic, space group Pnma, with unit-cell constants a = 8.131 (5), b = 16.34 (1), c = 4.142 (2) A and Z = 8. The crystal structure has been determined from Syntex automatic diffractometer data, using Patterson and Fourier syntheses, and refined by the least-squares method to a final R of 0.045. Sheets of (LaS), parallel to the [ 100] axis, are formed from LasS pyramids; between these layers, planes of S atoms are inserted, formed from S-S pairs in which the interatomic distance (2.104 A) indicates a covalent bond. The structure is related to a distorted arrangement of anti-Fe2As type.

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Provided enthalpy and volume changes at the transitions are accurate enough, it is possible to draw a p, T diagram that accounts for the stability hierarchy of polymorphs.