Phase diagram and crystal structures

l Sulphur compounds and complexes IX.1.1 Solid and gaseous thorium sulphides IX.1.1.1 Phase diagram and crystal structures 

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This chapter presents a review of the current data on phase diagrams and crystal structures of binary, ternary and quaternary metal antimonides with the R elements (R = Sc, Y and the lanthanides). 

Sologub, O.L., 1995, Interaction of holmium and germanium with platinum metals, silver and gold (phase diagrams and crystal structure of ternary... 

Boon, J.A., Carlin, R.T., Elias, A.M. and V lkes, J.S., Dialkylimidazolium-sodium chloroaluminate ternary salt system - phase-diagram and crystal-structure, J. Chem. Crystallogr. 25 (2), 57-62 (1995). 

Phase diagrams and crystal structures 74 3.4. Paramagnetic behaviour 103... 

Note There are three allotropes of carbon graphite, diamond, and buckminsterfullerene (Cgo) the latter, discovered in 1985, is composed of soccer-ball-shaped molecules. The thermodynamic stability of buckminsterfullerene has not yet been determined. The validity of its inclusion on the C phase diagram is, therefore, uncertain. (Metastable phases, such as supercooled water, do not appear on phase diagrams.) The crystal structure is face-centered cubic with Ceo molecules at the corners and faces of a cubic unit cell. The unit cell is shown below. 

The constitution of the C-Fe-Mo system is of great interest not only because molybdenum is one of the main alloying elements in tool and heat-resisting steels, but also because the complete C-Fe-Mo phase diagram is required in many other applications. Most of the available literature on the C-Fe-Mo system is devoted to investigation of the structure and properties of molybdenum steels. The data on phase relations and crystal structure of phases are presented mainly in the works listed in Table 1. 

Only two binary compounds, ScHg and ScHgs, are known in the Sc—Hg phase diagram. Their crystal structures have been determined by Laube and Nowotny (1963b) (table 8). 

The orthogonal arrangement of the disc-like molecules in the columns of and D id phases makes these phases uniaxial, while the tilted phases (Drd and Doh.d and Dt) are optically biaxial. There are two additional columnar phases labeled as and that have not yet been classified. The columnar phases were discovered before the observation of a nematic phase for disc-like molecules. Both chiral nematic phases and the re-entrant behavior have now been observed in discotics. The phase diagram and molecular structure of a typical discotic liquid crystal are shown in Fig. 1.11. Finally, it is noted that another classification scheme for the discotic mesophases has been used [1.26], which is based on the notation used for the conventional smectics. 

Common approaches for the tailoring of nonmetallic (ceramic) materials properties involve topochemical methods (those where the crystal structure remains largely unaffected) and the preparation of phases in which one or more sublattices are alloyed. In principle, such materials are within the realm of CALPHAD. On the other hand, as has already been stated, extrapolation does not really aid the discovery of new or novel phases, with unique crystal structures. Furthermore, assessed thermochemical data for the vast majority of ceramic systems, particularly transition metal compounds, are presently not available in commercial databases for use with phase diagram software. This does not necessarily preclude the use of the CALPHAD method on these systems However, it does require the user to carry out their own thermodynamic assessments of the (n — 1 )th-order subsystems and to import that data into a database for extrapolation to nth-order systems, which is not a trivial task. 

The crystal structures of 2-carboxypyrazine (1298) and 2,3-dicarboxypyrazine dihydrate (1299) have been determined and phase diagrams and data have been measured for the binary systems of 2-carboxypyrazine with benzoic acid (1300) nicotinic, isonicotinic, and picolinic acids (1301). The polarography of 2-carboxypyrazine has been examined (1302). Polarography of 2-amino-3-carboxypyrazine has been carried out in aqueous and nonaqueous solutions the reduction proceeds... 

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