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Ternary chlorides of the trivalent late lanthanides

Phase diagrams, crystal structures and thermodynamic properties

Journal of Thermal Analysis and Calorimetry
Author: H Seifert


A comprehensive review on phase diagrams, crystal structures and thermodynamic properties of ternary chlorides formed in the systems ACl/LnCl3 (A=Na, K, Rb, Cs) is presented. It continues an earlier review with the same contents on the lanthanides from La to Gd [1]. In both papers the author's own studies, published since 1985, together with original papers from other scientists are treated. With the three larger cations compounds of the composition A3LnCl6, A2LnCl5, ALn2Cl7 and beginning with holmium Cs3Ln2Cl9 are formed. With sodium the compounds Na3Ln5Cl18 (Ln=La to Sm) and NaLnCl4 (Ln=Eu to Lu) also exist. The stability of a ternary chloride in a system ACl/LnCl3 is given by the 'free enthalpy of synreaction', the formation of a compound from its neighbour compounds in its system. This must be negative. A surprising result is that the highest – melting compounds in the systems, A3LnCl6, are formed from ACl and A2LnCl5 with a loss of lattice energy, U. They exist as high-temperature compounds due to a sufficiently high gain in entropy at temperatures where the entropy term TΔS compensates the endothermic ΔH.

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Although melting is a most familiar physical phenomenon, the nature of the structural changes that occur when crystals melt are not known in detail. The present article considers the structural implications of the changes in physical properties that occur at the melting points, T m, of the alkali halides. This group of solids was selected for comparative examination because the simple crystal lattices are similar and reliable data are available for this physical change. For most of these salts, the theoretical lattice energies for alternative, regular ionic packing in 4:4, 6:6 and 8:8 coordination arrangements are comparable. Density differences between each solid and liquid at T mare small. To explain the pattern of quantitative results, it is suggested that the melt is composed of numerous small domains, within each of which the ions form regular (crystal-type) structures (regliq). The liquid is portrayed as an assemblage of such domains representing more than a single coordination structure and between which dynamic equilibria maintain continual and rapid transfers of ions. T mis identified as the temperature at which more than a single (regular) structure can coexist. The interdomain (imperfect and constantly rearranging) material (irregliq) cannot withstand shear, giving the melt its fluid, flow properties. From the physical evidence, it is demonstrated that the structural changes on melting are small: these can accommodate only minor modifications of the dispositions of all, or most, ions or larger changes for only a small fraction. This proposed representation, the set/liq melt model, may have wider applicability.

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An earlier published concept, showing correlations between the “average lattice energy” of glasses (i.e. their mean molar atomization enthalpy ΔA H at 298 K), the network dimensionalityD and some properties of different chalcogenide and oxide glasses, was used to interpret the transformation temperaturesT g of glasses containing fluorine or nitrogen instead of oxygen. A plot of Tg vs. ΔA H allows the comparison of completely different glasses from only one graph. Such a consistent evaluation of composition/property relationships is useful for the further improvement of fluoride and nitride glasses, which are important for applications in optics and telecommunications and as quality-limiting components in silicon nitride-based ceramics.

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Alkali hexamolybdochromates

Preparation, characterization and thermal behaviour

Journal of Thermal Analysis and Calorimetry
Authors: A. La Ginestra, R. Cerri, F. Giannetta, and P. Fiorucci

Li, Na, K, Rb, Cs and NH4 hexamolybdochromates have been prepared, characterized by X-ray and IR spectra, and their thermal behaviour was studied. We observed that the anion decomposition occurs only when the last 3 H2O are eliminated. TheΔH values for this elimination decrease from the Li to the Cs salt in the same manner as the lattice energies found in other alkali salts with a common anion. The exothermic reactions in the decomposition of the complexes are interpreted by inspection of the compounds obtained.

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: desorption of physically adsorbed and interlayer water, dehydroxylation of the lattice, and decomposition of interlayer anions. . The

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, Sattari , M , Tirandazi , B 2011 Prediction of crystal lattice energy using enthalpy of sublimation: a group contribution-based model . Ind Eng Chem Res 50 4 2482 – 2486 10.1021/ie101672j . 48

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.02.034 . 14. Zharkova , GI , Baidina , IA , Stabnikov , PA , Igumenov , IK . Trans-, cis-isomers of (1,1,1-trifluoro-2,4-pentandionato)Pt(II): volatility, structure and crystal lattice energy . J Struct Chem . 2006 ; 47

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-010-1085-1 . 10. Jenkins , HDB , Glasser , L 2002 Ionic Hydrates, M p X q · n H 2 O: lattice energy and standard enthalpy of formation estimation . Inorg Chem 41 : 378 – 388 . 11

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Interventional Medicine and Applied Science
Authors: Sergei N. Danilchenko, Aleksei N. Kalinkevich, Roman A. Moskalenko, Vladimir N. Kuznetsov, Aleksandr V. Kochenko, Evgenia V. Husak, Vadim V. Starikov, Fuyan Liu, Junhu Meng, and Jinjun Lü

crystal lattice, which depends on the level of imperfection and disorder in the structure of biominerals [ 21 ]. More ordered crystals (e.g., in mature bone) have much smaller lattice energy than low-mineralized apatites with numerous structural defects

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. 66. Gharagheizi , F , Sattari , M , Tirandazi , B . 2011 . Prediction of crystal lattice energy using enthalpy of sublimation: a group contribution-based model . Ind Eng Chem Res . 50 4 2482 – 2486 10

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