High Temperature Phase Diagram and Enthalpies of Solution of TmSe

Abstract

As we have shown in the past TmSe, a mixed valent compound, has a large homogeneity range (1,2,3,4). Variation of nonstoichiometry leads to a large change of the Tm-valence (approx.25%) and therefore induces fascinating physical properties (1,5). Their interpretation however is not yet complete due to the lack of a theoretical model for the 4f-5d hybridization. In principle, it is also possible that some of the properties attributed to a homogeneous sample of a mixed valent compound result from the existance of several phases. In order to investigate the “homogeneity” of the nonstoichiometric range of TmSe and the phase relationships as a function of temperature, three kinds of investigations have been carried out. Structural, including single crystal presession photographs and electron diffraction, T-x phasediagram up to 2300 C, and calorimetric measurements (heats of reaction of TmSe with 4n HCl) as a function of nonstoichiometry.