Defects in solid state lattices an introduction

This expression has its origins in the Bom Lande equation, with a value of 9 for the Bom exponent (the value for NaCl) and half the value of the Madelung constant for NaCl the inclusion of the factor v shows why half of A is included. Although the Kapustinskii equation is useful, it is a gross approximation and values obtained in this way must be treated with caution. 

The net result is that AH° for the disproportionation reaction shown in equation 6.25 is negative. 

A problem in estimating the lattice energy of a hypothetical compound is deciding what ionic structure type to assume. Attempts have been made to use the fact that Madelung constants for MX and MX2 structure types (Table 6.4) are in an 

So far in this chapter, we have assumed implicitly that all the pure substances considered have ideal lattices in which every site is occupied by the correct type of atom or ion. This state appertains only at OK, and above this temperature, lattice defects are always present. The energy required to create a defect is more than compensated for by the resulting increase in entropy of the structure. There are various types of lattice defects, but we shall introduce only the Schottky and Frenkel defects. Solid state defects are discussed further in Chapter 28. Spinels and defect spinels are introduced in Box 13.6. 

The thermochemical cycle to be considered is given in equation 5.25, in which the values of AaiT°(Ca,s) (178kJmoC ) and the difference between lEi and IE2 for Ca (—555kJmor ) are significantly smaller in magnitude 

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Chapter 6 Defects in solid state lattices an introduction 177... 

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