TmSe g

The entropy of TmSe(g) at 298.15 K was calculated to be S°(TmSe, g, 298.15 K) = 272.0 J-K -mol by Kovalevskaya, Sidorenko, Lysenko, and Fesenko [77KOV/S1D]. The entropy value is not selected because all parameters required for the calculation using statistical mechanics were estimated. 

The dissociation enthalpy of TmSe(g) was estimated to be A, //° (TmSe, g, 0 K) = (270 40) kJ-moP by Bergman, Coppens, Drowart, and Smoes [70BER/COP] by comparison with other lanthanide selenides. No value of the enthalpy of formation of TmSe(g) is selected. 

---

The form taken by the resistivity rise at low temperatures in the ICF metallic phase has not yet been satisfactorily analyzed. Fig.3 shows that a p a exp relation makes fair representation of the data (38) for SmS at 20 kB. For lOkB, SmS is not properly converted at the lowest temperatures (Ref. 38, inset to Fig. 2) and the sigmoid deviation shown could be ascribed to this cause. However none of the data presently available for ICF metals (e.g. SmBg, TmSe), seems to express an exponential run away in resistivity to low temperatures. It is possible that the observed flattening off marks the limit set by surface conduction, via permanently and fully... 

Kaldis, E., and B. Fritzler, 1982, Valence and phase instabilites in TmSe, crystals, in Progress in Solid State Chemistry, Vol. 14, eds G.M. Rosenblatt and W.L. Worrell (Pergamon Press, Oxford) pp. 95-139. 

Thermal conductivity of systems with an intermediate valence One could expect nonstandard behaviour of L(T /Lq in these systems too. Unfortunately, this case has not been discussed theoretically and it is not possible to draw any conclusions from the analysis of experimental data on thermal conductivity. In the classical compounds with an intermediate valence of the lanthanide atoms (SmBg, TmSe) kl > (especially in the low-temperature region). The contribution of to K,ot has not been taken into account during investigations of metals from this class of materials [e.g., CePdj (Schneider and Wohllcben 1981)]. 

Fig. 27. Gd ESR linewidths (peak to peak distance of the absorption derivative left frames, a-c) and g-values (right frames, d-f) for TmS (a,d), TmTe(b,e) and TmSe(cJ). From Huang and Sugawara (1977).

Here / and are the relative fractions of the normalized absorption jumps in the 4f" and 4f" reference spectra and m is the number of outer valence electrons. This procedure was applied e.g. by Launois et al. (1980), Martin et al. (1980), Ravot et al. (1981) to extract the valence from the L, spectra of mixed valent lanthanide chalcogenides. Figure 14 reproduces the spectra of mixed valent TmSe together with its (isostructural) references TmS (nominally 3" ) and TmTe (nominally 2" ). Divalent Tm in TmTe exhibits a smaller and narrower line than trivalent Tm in... 

Electronic properties of TmSe. In the early days of research on intermediate-valent TmSe a lot of diserepaneies occurred between the main research centers of that time, AT T and IBM, about the physical properties and degree of valence mixing of TmSe (see, e.g.. Parks 1976). The reason was that TmSe exists with various stoichiometries and the stoichiometry had not been controlled in the 1970 s. However, there was never a question that TmSe can be prepared in an intermediate-valent form and in fig. 61 we show a XPS spectrum of TmSe where the divalent and trivalent final state spectra can be discerned with their typical ladder-like structure. 

Fig. 193. Electrical resistivity q of nearly stoichiometric TmSe at pressures up to 32.5 kbar versus temperature. The pressure dependences of q at 300 K (inset ) and of the slope -dg/dln T (inset (g)) are given in Fig. 193a.

The sesquiselenide of orthorhombic SC2S3 structure type is homgeneous between TmSe 43 and Tm2Se3, Guittard et al. [6]. The lattice constant is a = 5.671 A (presumably for the cubic subcell). The measured density is 6.933 0.004 g/cm , the microhardness -340kg/mm2 ( 333x10 Pa). Kaldis, Fritzler [3]. 

The formation of Tm202Se on the (100) surface of TmSe after exposure to 0.5 L O2 is suggested to explain the change of the photoemission spectra (appearance of pure Tm " spectra). It extends over more than one surface layer on exposure to 1.5 L O2, G. Kaindl, C. Laubschat, B. Reihl, P. A. Poliak, N. M rtensson, F. Holtzberg, D. E. Eastman (Phys. Rev. [3] B 26 [1982] 1713/27,1715 Valence Instab. Proc. Intern. Conf., Zurich. Switz., 1982, pp. 281/5). 

---