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Heterobimetallic [Ni(salen)Ln(hfa)3] species [H2salen and Hhfa being N,N′‐ethylenebis(salicylideneimine) and hexa‐fluoroacetylacetone respectively], where Ni(salen) acts as a neutral chelating ligand towards LnIII, form a series of isostructural compounds for Ln = YIII and any lanthanideIII cation from La to Yb. They are also isostructural with some of the [Cu(salen)Ln(hfa)3] compounds. They sublime without decomposition under vacuum which makes them potential single‐source precursors in MOCVD. Sublimation, thermal behaviour, pressure and composition of the vapour phase versus temperature have been studied for the yttrium derivative, by means of thermal analyses, and mass spectrometry using a Knudsen cell. The dissociation process [Ni(salen)Y(hfa)3] = Ni(salen) + Y(hfa)3 has been thermodynamically investigated. Information on the solid‐state intermolecular interactions in relation with volatility was obtained through the crystal structure determination of the gadolinium derivative. A comparative structural study of [Ni(salen)Gd(hfa)3] and [Cu(saloph)Y(hfa)3], [H2saloph is N,N′‐o‐phenylenebis(salicylideneimine)], allows to under‐stand why the latter is less volatile than the former despite similar molecular and solid‐state structures.

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Subject classification: 64.60.-i; 64.70.Hz; S8.13 P-T-X data are the thermodynamic basis for modeling the crystal growth of materials with controlled stoichiometry. In this paper results of the first direct experimental measurement of the total vapor pressure are reported for three-phase equilibria SLV (solid-liquid-vapor) and VLS (vaporliquid-solid) in Zn-Te, and the P-T projection of the P-T-X phase diagram is constructed. Geometrical analysis of the phase equilibrium showed that three congruent processes are observed in the Zn-Te system: congruent melting (S = L), sublimation (S = V), and vaporization (L = V). All three congruent curves are tangent to SLV. Consequently, all three congruent points are on the Teside of the maximum melting point of ZnTe. The vapor pressure scanning method was applied to determine the maximum non-stoichiometry as a function of the temperature. The solidus volume of ZnTe was shown to be on the Te-side of the stoichiometric plane.A crucial issue for high-quality single crystal growth of non-stoichiometric materials, such as II-VI semiconductors, is the temperature and pressure dependence of the crystal composition. This information is contained in the P-T-X (pressure-temperaturecomposition) phase diagram. For the Zn-Te system, the T-X projection of the P-T-X diagram was constructed by Steininger et al.[1] from DTA data. The P-T projection of this diagram was studied by Shiozawa et al. [2] by visual observation of the melting points of (ZnTe + Te) and (ZnTe + Zn) samples in sealed quartz tubes placed in a twotemperature furnace. Subsequently, Brebrick [3, 4] measured optical absorption of the vapors over Zn-and Te-saturated ZnTe, and Jordan and Zupp [5] calculated the vapor pressure along the liquidus curve in the Zn-Te system and evaluated the solidus of ZnTe.In this paper, the first direct vapor pressure measurements are reported for the Zn-Te system. The P-T projection was constructed and the maximum Zn non-stoichiometry in ZnTe was determined by the vapor pressure scanning method.The total vapor pressure in the Zn-Te system was measured with a quartz Bourdon gauge in the temperature range T 1100 C and pressure up to 760 mm Hg. Precision of the (P, T) measurements was AE0.5 C and AE0.1 mm Hg. The experimental procedure was similar to that described earlier [6,7]. Two-phase (ZnTe + Zn) and (ZnTe + Te) samples were prepared via direct high-temperature high-vacuum synthesis from extra pure elements weighed out to the nearest 5 Â 10 --5 g. The total impurity content in both 1 ) Corresponding