SmSe compounds

Fig. 14.4 ASmGeSe4 compounds viewed parallel to the SmCeSe4 layers. Dashed lines indicate unit cell boundaries in each case. CeSe4 tetrahedra are drawn as tetrahedral solids, and the SmSe environments are drawn using a ball-stick model. In all...

Such compounds have a continuous transition from 0 to 50-60 kbar. Like SmS, Ivanchenko et al. (1971) and Lashkarev and Ivanchenko (1972) have studied SmSe and SmTe amorphous thin films. 

On the other hand, Singh et al. (1976, 1977) have studied SmSe thin films by electron microscopy and electrical resistance. They found a new compound with a hexagonal cell, which was obtained after annealing at 470 K. This lattice, as deduced from electron diffraction patterns, seems quite curious. Indeed, the authors interpret the presence of two rings as (00.1) and (00.3) by a double diffraction effect. But the rings relative to (00.2) or (00.4) are not observed, and this destroys their hypothesis. Moreover, the more intense ring of the pattern corresponds to the (222) diffraction of C-SmzOs. 

Singh and Srivastava (1977) have observed, as for SmSe, the formation of a curious YbSe compound with a hexagonal cell, with lattice parameters larger than the ones for SmSe. 

TABLE 5 Calculated transition pressures for the electronic and structural phase transitions in the Pr pnictides and chalcogenides of Pr, Sm, Eu, Tm, and Yb. Also quoted are the volume discontinuities (relatively to the zero pressure equilibrium volume) at the transition. The notation (f") refers to SIC-LSD calculations with n localized f-electrons. Experimentally, the transitions of SmS are discontinuous, while those of SmSe, SmTe, EuO, EuS, and the Tm and Yb chalcogenides (at room temperature) are continuous. The volume changes for SmSe and SmTe as well as TmTe are obtained by extrapolation over the transition range. For Yb compounds, we quote the relative volumes at which the delocalization starts... 

In this section we summarize the various theories and models that have been proposed to explain the y a transition of cerium. These models are discussed with emphasis on their consistency with the experimental results described in the preceding sections. The y a transition in cerium is often classed with the change-of-valence transitions observed in SmS, SmSe, CeP, and certain other rare earth compounds. Some of the numerous theories which attempt to explain these transitions apply equally well to cerium. However, since these transitions are treated in ch. 20 they will not be described here, except for those theories which have been specifically ascribed to cerium by their authors. 

Later susceptibility measurements by Beeken and Schweitzer (1981) on SmS, SmSe and SmSe-Sm As mixed compounds did not confirm the simple Curie-Weiss behaviour as found by Didchenko and Gortsema (1963). Figure 76 shows the susceptibilities of SmSe and SmAs and some mixed compounds. The authors try to analyze these curves by the superposition of a Sm +(J = 0) ion susceptibility taking into account J-mixing, and a Curie-Weiss contribution of magnetic impurities, which becomes visible at low temperatures. 3% of Sm + ions would explain the results. However, the same explanation is not valid for measurements on SmS. 

In SmSe, the Sm " ion has a magnetic moment varying with the temperature. Values for the constants of the Curie-Weiss law given in the table are therefore very crude. The susceptibility of SmSe between 143 and 193 K shows only minor variations from the straight line (1/x vs. T), apparently with the antiferromagnetic type, landelli [4]. The GdSe sample studied by [4] showed a high Increase of Xmoi within 353 and 263 K. This may be due to metal dispersed in the mass of the compound. 

MSe compounds with trivalent M = Sc, Y, La to Lu except Sm, Eu, and Yb have metallic luster, whereas SmSe, EuSe, and YbSe have a dull appearance. With the metallic phases, the color of inhomogeneous products was more intense than of homogeneous products, landelli [1]. 

The liquidus of the SmSe-GajSej state diagram (Aliyeva et al. 1987) consists of three branches which corresponds with the primary crystallization of the phases SmSe, SmGa2Se4 and Ga2Se3. The ternary compound is formed according to the peritectic reaction,... 

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