The SmSe-NdSe System

A continuous series of mixed crystals is formed in the Smi xNdxSe system, as shown by X-ray diffraction studies on samples, prepared by a (explosion-induced) dynamical high pressure technique, Batsanov etal. [1]. Sm. Nd Se crystals may be prepared by reaction of the elements at 500 to 800°C and subsequent melting in tantalum or molybdenum containers in an inert gas atmosphere, followed by slowly cooling, Matson etal. [2]. Films in the composition range from x = 0 to x = 0.15 are obtained by thermal coevaporation of the elements at 5x10 Torr, deposited on Pyrex or CaFg substrates, which are heated to 473 or 673 K, Dumas, Schlenker [3]. 

The cell size in the SmSe-NdSe system changes gradually from SmSe to NdSe, Miller et al. [4, p. 18]. The lattice constants for Sm. NdxSe mixed crystals with cubic NaCl structure versus X are shown in Fig. 73 together with the color of the samples. The following numerical values are determined as a function of x in Sm. Nd Se  

The deviations from Vegard s law, as shown in the figure, are due to the change of the samarium valence, Welber, Jayaraman [5]. A similar curve of the lattice constants for samples obtained by a dynamical high pressure method is given by Batsanov et al. [1]. No variation of a (=6.20 A) is observed on films between x = 0 and 0.15 because of the inaccuracy of the measurements by Dumas, Schlenker [3]. The shift of the line in the X-ray spectrum of Smi xNdxSe mixed crystals remains close to zero (i.e., no isomorphous phase transition occurs), for a figure, see the paper, Sumbaev [6]. 

The following melting points t of Smi xNdxSe are observed by Miller etal. [4, p. 11]  

Some crystallographic models for the description of electrical properties are proposed by Reid etal. [7], Miller etal. [4, pp. 38/41]. According to more recent resistivity studies, the semiconductor-metal transition region is observed on samples with a much lower Nd concentration, even at 1 at.% Nd the SmSe appears to be degenerated, Welber, Jayaraman [5]. 

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