Abstract: The existence of a Tm3+Te ((4f)12) compound with the NaCl structure and the lattice constant a = 6.04 Å has been reported several times in the literature for polycrystalline samples. Single crystals of pure Tm2+Te ((4f)13) grown from the melt at 1950 °C also have the NaCl structure but the lattice constant is much larger (a = 6.36 Å). In this paper we investigate the possibility of changing the valence in TmTe by varying the stoichiometry. X-ray and chemical analyses show that the Tm3+ monotelluride is strongly deficient in thulium, has the Sc2S3 superstructure of the NaCl lattice and has the composition Tm0.68Te (TmTe1.47). Density and magnetic susceptibility data support this result and show the trivalent character of thulium. The compound is stable at both low and high temperatures so that single crystals can be grown at T ⩽ 2000 °C. This phase is the only reaction product of the elements at 500 °C ⩽ T ⩽ 800 °C. We believe that the Sc2S3 superstructure has not been recognized in the past because of the very low intensity of the extra reflections in the X-ray film. The transition from Tm2+Te to Tm3+0.68Te takes place via a miscibility gap and a slightly deformed NaCl structure (contraction along the diagonal owing to the increasing Tm3+ contribution) with a rhombohedral cell and lattice constants a ≈ 6.145 Å and a ≈ 89.08°. Single crystals of this phase were grown from the melt at T ≈ 1920°C. The end phases Tm2+Te (NaCl structure) and Tm3+0.68Te (Sc2S3 structure) do not show appreciable solid solubility ranges and probably have integral valence. Extended Tm2+xTm3+1−xTe solid solutions, which would allow mixed valence, do not exist.

EXPLOR_STEP=$WICRI_ROOT/Wicri/Terre/explor/ThuliumV1/Data/Main/Merge

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{{Explor lien
   |wiki=    Wicri/Terre
   |area=    ThuliumV1
   |flux=    Main
   |étape=   Merge
   |type=    RBID
   |clé=     ISTEX:6A1A65E7EBB6B979273DE3D592DAF81EBC14BD18
   |texte=   The search for a trivalent thulium monotelluride
}}