Lanthanide elements chalcogenides

Quaternary chalcogenides of the type A Ln M X, containing three metal elements from different blocks of the Periodic Table (A is an alkali or alkaline earth metal, Ln is an /-block lanthanide or scandium, M is a p-block main group or a r/-block transition metal, and X is S or Se) are also known [65]. 

FIGURE 1 Lattice constants of the elemental lanthanides (top), their chalcogenides (middle) (after Jayaraman, 1979), and pnictides (bottom). For the elemental lanthanides, it is the atomic sphere radius, 5, that is shown instead of the lattice parameter, where S is defined as V = 4/3tiS with V the unit cell volume. 

The jumps in the lattice constants in Figure 1, seen for the elemental Eu and Yb, as well as at the chalcogenides of Sm, Eu, Tm, and Yb, are due to the change in valence from trivalent to divalent. If a transition to the trivalent state were to occur, the lattice constant would also follow the monotonous behaviour of the other lanthanides, as seen in Figure 2, where the ionic radii of trivalent lanthanide ions are displayed. For the pnictides, only CeN shows an anomaly, indicating a tetravalent state, whereas all the other compounds show a smooth, decreasing behaviour as a function of the lanthanide atomic number. 

The isomorphism of the lanthanide and actinide B1 compounds allows the bond-length variation to be visualized by simply plotting the lattice parameters. This was done in fig. 2 for the monocarbides (a), the monopnictides (b), and the mono-chalcogenides (c). As in the case of the pure actinide metals (Manes and Benedict 1985), bond shortening is observed for the actinides Pa to Pu, with respect to the other actinides and to the corresponding lanthanide compounds. This effect is most clearly marked for the compounds with the lighter non-actinide elements (e.g. N, P, S, Se) and becomes weaker with increasing Z of the non-actinide partner. Like in... 

The following chemical symbols are used in this chapter R designates the rare earth elements, including the lanthanides, yttrium and scandium M stands for the elements of group I (lithium, sodium, calcium, rubidium, cesium, copper, silver), X is used to designate chalcogenides (sulphur, selenium, tellurium). 

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