Point binary oxides

First-order estimates of entropy are often based on the observation that heat capacities and thereby entropies of complex compounds often are well represented by summing in stoichiometric proportions the heat capacities or entropies of simpler chemical entities. Latimer [12] used entropies of elements and molecular groups to estimate the entropy of more complex compounds see Spencer for revised tabulated values [13]. Fyfe et al. [14] pointed out a correlation between entropy and molar volume and introduced a simple volume correction factor in their scheme for estimation of the entropy of complex oxides based on the entropy of binary oxides. The latter approach was further developed by Holland [15], who looked into the effect of volume on the vibrational entropy derived from the Einstein and Debye models. 

Photolysis then proceeds by rapture of the 0-0 bond and loss of CO to generate 02Fe(C0)3. Later oxocarbonyl intermediates are difficult to characterize since they are invariably formed only in meagre quantities. However, the nature of the final molecular binary oxide products does appear to have been resolved. They are the peroxo iron(ll) species () -02)Fe and the planar (or near planar) iron(Vl) oxide FeOs. Taken together the results point to the reaction scheme shown in Scheme 5 for the matrix photooxidation of Fe(CO)s in Ar or CH4 matrices containing O2 at 20 K. 

This approach makes it possible to describe several structural features of anion-deficient fluorite-related binary oxides of Ce, Pr and Tb but it is fundamentally descriptive rather than predictive. This limit was pointed out by Khang and Eyring who recently built a model that is also capable of predicting the structural features of unknown phases in the series... 

The same publication reports on nonlinear dependence between pitting potential of ion-implanted binary surface alloys of aluminum and zero points of oxides of implanting metals. 

The mechanism of a solid state reaction or the transport mechanism of the reacting atoms is measured in a diflFusion-couple experiment. An example of the growth of a ternary spinel from separate binary oxides will be sketched below. The discussion of point defects and their behavior and concentration in Section 10.3 provides the physical chemistry background for this discussion of reacting atoms. 

Kubaschewski (1972) collected and compared the enthalpies of formation of complex oxides from binary oxides. He did not offer any systematic correlation of these enthalpies with structural properties. Hoppe (1966,1970a, b, 1975) developed the MAPLE concept (Madelung part of lattice energy) as a tool to guide the structural interpretation of bonding in complex oxides and halides. It requires as input parameters the unit cell of a compound and positions of all atoms, and it treats the crystal as an ionic array of point charges. If crystal structure determinations have been properly done, MAPLE calculations for a complex compound are within 2% (sometimes larger, sometimes smaller) of the MAPLE values of the binary (parent) compounds. Therefore, purely ionic-model calculations are not suflftciently sensitive to correlate quantitatively with the relatively small enthalpies of solid-state complexation. 

In this chapter, we will discuss the generation modes of thermodynamically stable point defects and the defect-chemical logic to calculate the equilibrium defect structure of a given system. As a stereotype of systems, we will consider only a binary oxide MO, but the idea and logic can be readily extended to other binary, ternary and higher systems with minor modifications [2-6]. 

Thorium oxide ThO has the highest melhng point (3300°C) of all the binary oxides and has found some uses in special refractory applications. 

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