The YbSe-TmSe System

The structures of solid solutions prepared at 1300°C derive from the face-centered cubic YbSe lattice. A rhombohedral distortion is perceptible above the composition YhSe 13. The rhombohedral angle decreases from 33°32 to 32°37 between YbSei 13 and YbSe 33. The volume of the unit cell decreases linearly between YbSe and YbSei 33, Souleau etal. [1], Guittard et al. [2]. 

The dark violet Yb2Se3 crystallizes in the orthorhombic SC2S3 structure type with a = 11.27, b = 8.02, c = 23.98 A. The structure is related to the NaCl type and formed from this by ordered removal of Vs of the cations. The Yb atoms are surrounded by six Se in a slightly distorted octahedron [1]. Epitaxially grown monocrystalline films on the (111) face of CaFg crystallize in the NaCl type with a = 5.654 0.002 A, Suryanarayanan et al. [6], Paparoditis, Suryanarayanan [5]. 

Calorimetrically determined thermochemical data for the formation from the elements under standard conditions are AH298=-230.8 7.4, AG298=-226.1 kcal/mol, AS298=-13.0 and S298 = 47.5 cal- mol . The data for atomization are AH298 = 462.2, AG298 = 395.1 kcal/mol 

The Yb2Se3 films are amber by transmission and transparent below 3 eV. Studies of the magnetic circular dichroism indicated the paramagnetic properties of Yb2Se3, later confirmed by direct measurements (see p. 43). The films contain essentially Yb and no Yb ions [5, 6]. 

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