Stability of solid solutions

As with decreasing of the cation average ionic radius the electrical conductivity of solid solution samples on the basis of Zr02 increases and stability of solid solution deceases [4] and one of the most important demands that are made to the solid electrolytes is a combination of high electrical conductivity with the ageing stability (R /Ro), the ageing of investigated solid electrolytes was studied in the present work. 

Vasilliev V. P., Mamontov M N., Bykov M. A. (1990). Thermodynamic properties and stability of solid solutions CdTe-HgTe-Te system, Vestnik Moskovskogo Universiteta, serie2. Chemistry, Vol. 31, No.3, pp. 211-218. (in Russian)... 

The difference in stability between FeO and NiO is not as large as that between iron and copper oxides, and so the preferential oxidation of iron is not so marked in pentlandite. Furthermore, the nickel and iron monoxides form a continuous series of solid solutions, and so a small amount of nickel is always removed into die oxide phase (Table 9.2). 

Intimate mixing of the components can lead to the formation of compounds or of solid solutions of the components which are difficult to reduce at 300°C but which, when reduced, contain well dispersed and well stabilized nickel. Methanation catalysts in practice therefore are compromises which combine optimum reducibility with activity and stability. As an example of compound formation, alumina readily forms with nickel... 

A consideration of natural occurrence and chemical composition of alkali zeolites allows a certain refinement of the zeolite facies concept previously proposed. The key factor is the grouping of the alkali zeolites into a continuous solid solution series. Other possible coexisting phases of similar composition are sodium and potassium feldspar, natrolite and analcite. The extent of solid solution decreases with temperature, possibly also with pressure. This effect allows the sequential series zeolite-K feldspar, zeolite-analcite-K feldspar, analcite-K feldspar-albite and eventually two feldspars to the exclusion of analcite, the alkali zeolite with the highest stability limits. 

Kolokassidou, C., Pashalidis, I., Costa, C. N., Efstathiou, A. M., and Buckau, G. (2007). Thermal stability of solid and aqueous solutions of humic acid. Thermochim. Acta 454(2), 78-83. 

Fig. 19. Schematic T-Xi -X2 diagram of the Cu-Mo-S system. Temperature stability and solid solution widths of the X-phase ( CuMo2S3) in the Cu-Mo-S system are displayed. To simplify the perspective drawing a few isotherms are indicated with a projection onto the base, demonstrating the whole compositional X-phase solid solution...

Pniim-Fniim transformations of solid solutions of CsCl with KC1 and CsBr exhibit different behaviours. With increasing percentages of KC1, the NaCl structure gets stabilized in the CsCl+KCl system. In the CsCl+CsBr system, the transformation temperature increases with % CsBr and AH essentially remains constant. Both these behaviours can be satisfactorily explained in terms of the Born treatment of ionic solids. The Pmlm-Fniim transformation retains its first-order characteristics in the CsCl+KCl system, but higher-order components seem to be present in the CsCl+CsBr system. Incorporation of vacancies do not affect the transformation of CsCl markedly. 

The value of (8bl + 6b2) thus calculated is 76867 x 10-12 ergs mol-1. The A /ss of solid solutions of CsCl and CsBr were evaluated (eqn. (1)) for different values of b2 (in the range 0-900 x 10-12 erg mol-1) using the r0 values from table 2. The results are shown diagramatically in fig. 3, the values of b, and b2 are 9257 x 10-12 and 468 x 10-12 erg mol-1 respectively when (6b2/%b1 + 6b2)csci (6b2l%bi + 6b2)csB,- The AUs s remains nearly constant with the % CsBr when b2 is between 400 and 500 x 10-12 erg mol-1. Thus, curves 3 and 4 of fig. 3 closely represent the experimentally observed situation. Thus, the Born model of ionic solids describes the relative stabilities of structures of alkali halides in widely different situations as manifested here by the CsCl+KCl and CsCl + CsBr systems. 

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