Stoichiometry chalcogenides

Table 7.9 Stoichiometries and stmctures of the crystalline chalcogenides of Group 13 elements...

All three metals form a wide variety of binary chalcogenides which frequently differ both in stoichiometry and in structure from the oxides. Many have complex structures which are not easily described, and detailed discussion is therefore inappropriate. The various sulfide phases are listed in Table 22.4 phases approximating to the stoichiometry MS have the NiAs-type structure (p. 556) whereas MS2 have layer lattices related to M0S2 (p. 1018), Cdl2, or CdCl2 (p. 1212). Sometimes complex layer-sequences occur in which the 6-coordinate metal atom is alternatively octahedral and trigonal prismatic. Most of the phases exhibit... 

Zinc chalcogenide thin hlms have been grown by ECALE using zinc sulphate as metal source and sodium sulphide and sodium selenite as chalcogenide precursors.145-148 The formation of the hrst layers of ZnS on (lll)Au has been analyzed by STM and XPS.145 HRSEM images showed that the him surface was very hat, even at an atomic level. On the other hand, thicker ZnS hlms were formed of well-separated crystal nuclei. The stoichiometry of a thicker ZnS him showed a slight excess of sulphur, with a Zn S ratio of 1 1.2. The band gap of a thicker him (deposition time 12 h) was 3.60eV.147... 

Plutonium(IV), hydrolysis of, 19 698 Plutonium-231, 19 670 Plutonium-238, 19 668, 669, 675 special precautions for, 19 703 Plutonium-239, 19 669 Plutonium aqua ions, thermodynamic values for, 19 693t Plutonium carbide, 4 649t stoichiometry, 4 651 Plutonium carbide (2 3), 4 649t Plutonium carbides, 19 690-691 Plutonium cations, 19 692 Plutonium chalcogenides, 19 691 Plutonium complexes bonding in, 19 694—695 formation constants for, 19 697t... 

Along with the MC, the fatty acid is regenerated upon exposure to the dihydrogen-chalcogenide. Much quantitative and qualitative experimental data have been reported that supports the stoichiometry depicted in Eq. (4). As discussed in a later section, however, there is also considerable evidence that the reaction does not proceed to completion as depicted in Eq. (4). 

The only other crystallographic result reported for a berkelium chal-cogenide besides those summarized in Table II is a cubic lattice parameter of 0.844 nm for Bk2S3 (155). The microscale synthesis of the brownish-black sesquisulfide was carried out by treatment of berkelium oxide at 1400 K with a mixture of H2S and CS2 vapors. In later work (136,137), the higher chalcogenides were prepared on the 20- to 30-jug scale in quartz capillaries by direct combination of the elements. These were then thermally decomposed in situ to yield the lower chalcogenides. The stoichiometries of these compounds have not been determined directly. 

In Anderson s treatment, no account is taken of changes in the electronic disorder of the compound arising from changes in the stoichiometry. In the sense of the notation used previously this is equivalent to considering the presence of only neutral defects. For a binary compound exhibiting only Frenkel disorder in the metal lattice, the defects are therefore Vm° and Mf, with no defects in chalcogenide lattice. The presentation given here is equivalent to that of Anderson, since we can write ... 

Many ionic compounds of AX2 stoichiometry possess the CaF2 (fluorite), or Na20 (antifluorite) structures shown in Figure 3.15. Fluorite is similar to CsCl, but with every other eight coordinate cation removed. Each fluoride anion is tetrahedrally coordinated by calcium ions. This structure is adopted by several fluorides and oxides. In the antifluorite structure, the coordination numbers are the inverse. Most oxides and other chalcogenides of the alkali metals (e.g. Na2Se, K2Se) possess the antifluorite structure, but so do some more covalent compounds, such as the silicides of Mg, Ge, Sn, and Pb. 

Table 5 Stoichiometries and structures of the crystalhne chalcogenides of gallium...

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