Resistivity and Hall effect are measured on GaTexSe1–x crystals (0 ≦ x ≦ 1) grown by the Bridgman‐Stockbarger method. These p‐type materials exhibit a discontinuity in electrical properties between x = 0·25 and 0·63. In this interval a strong variation of the resistivity and of the activation energy Ea of the acceptors is observed.

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The crystal structure of a-P 4 S 3 has been investigated as a function of temperature from 4 Κ to 309 Κ by X-ray and neutron diffraction. Powder diffraction shows that there are no transitions below 314 K. The bond distances of the P 4 S 3 molecule have been determined very precisely. Refinements show that the temperature variation of the intramolecular distances is negligible whereas the intermolecular distances change significantly (about 1 % in the temperature range 120 to 193 K) indicating that the P4S3 molecules can be considered as rigid molecules. The librational and translational amplitudes of the rigid P 4 S 3 molecules have been obtained as a function of temperature by constrained refinement, and significance tests on the neutron results support the rigid-body assumption. It has been found that the librational amplitudes of P 4 S 3 molecules about the threefold axis predominates as the crystal-to-plastic (oí-*β) transition is approached, suggesting that the plastic phase may be initially a uniaxial-rotator phase stabilised by a weak molecular dipole moment.

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