Terbium lattice parameters

Tb-Cu-Sb. A ternary compound of terbium with copper and antimony of the 3 3 4 stoichiometric ratio was identified and studied by means of X-ray analysis by Skolozdra et al. (1993). Tb3Cu3Sb4 was found to have the Y3Au3Sb4 type structure with a lattice parameter of a = 0.9522 (X-ray powder diffraction). For experimental details, see the Y-Cu-Sb system. 

In 1923 CeC>2 was found to have the fluorite structure (Goldschmidt and Thomas-sen, 1923), and in 1926 PrC>2 was found to have the same structure (Goldschmidt, 1926). In 1950 the intermediate compositions in the PrO system were reported to have the fluorite structure of variable lattice parameters (the superstructure reflections were not observed). In 1951 TbC>2 was also shown to have the fluorite structure (Gruen et al., 1951). By this time the basic fluorite structure had been established for all the known higher oxides of cerium, praseodymium and terbium. 

The berkelium monopnictides have been prepared on the multimicrogram scale by direct combination of the elements (138). In all cases, the lattice constants of the NaCl-type cubic structures were smaller than those of the corresponding curium monopnictides but comparable to those of the corresponding terbium compounds. This supports the semimetallic classification for these compounds. One additional report of BkN has appeared (139). The lattice parameter derived from the sample exhibiting a single phase was 0.5010 0.0004 nm, whereas that extracted from the mixed-phase sample of BkN resulting from incomplete conversion of a hydride was 0.4948 0.0003 nm. Clearly, additional samples of BkN should be prepared to establish more firmly its lattice constant. 

The lattice parameter of the compounds R3 MC in the lanthanide series for a given element M changes linearly with the radius of the trivalent rare earth ions, following the lanthanide contraction regularity, except for europium and ytterbium which appear to have a variable-valence state. In the ytterbium-M (Al, Ga, In, Tl)-carbon system, the unit cell volume of the compound YbgMC, is larger than the value expected from the relationship mentioned above. In the europium-M(Al, Ga, In, Tl)-carbon system no compound was found. For the compounds of yttrium, as expected, the lattice parameter falls between those of the respective terbium and dysprosium compounds. 

A ternary compound of terbium with gold and germanium in the stoichiometric ratio 1 1 1 has been identified and studied by means of X-ray and metallographic analyses by Rossi et al. (1992). TbAuGe was found to adopt the LiGaGe type with lattice parameters a = 0.4416, c = 0.7335. For the experimental procedure see GdAuGe under Gd-Au-Ge. 

The lattice spacing information that has been reported for the lanthanum-terbium system is shown in figs. 9 and 10 for the a and c lattice parameters, respectively. The reported data are concentrated in the lanthanum- and terbium-rich ends of the system with no data between 20 and 90 at% terbium. 

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