Lattices defects summary

In summary, it is important to determine crystal quality, unit cell dimensions of the crystal (a larger crystal absorbs X rays more strongly, 0.3-0.5 mm is considered the optimal size), the crystal s space group, and how many protein molecules are in the unit cell and in one asymmetric unit. Actually, the great majority of crystals useable for X-ray crystallography are not ideal but contain lattice defects. This is true for protein crystals, which are also weak scatterers since the great majority of the component atoms are light atoms, C, N, and O. 

R. S. Eachus, R. Janes, and M. T. Olm, Papers Summaries, in Fifth Europhysical Topical Conference on Lattice Defects in Ionic Crystals, Madrid, 1986, p. 259. 

In summary, these experiments demonstrate that Ba2 partitioning does not depend on the concentration of Ba2 over the broad range tested and that it is unaffected by moderate amounts of Sr2. Substantial quantities of NaCl decrease kcBa and rapid precipitation increases kcBa. These results suggest little or none of the Ba2 is incorporated in Ca 2 lattice sites in calcite, but instead adsorbs on surfaces and defects and is trapped by growth of the crystal. 

As is common when dealing with ceramics, we use the Kroger-Vink notation throughout this chapter to describe lattice and electronic defects. A summary of this notation is given in the appendix. 

In summary then, we see that theoretical estimates which take account of the elastic relaxation of the surrounding lattice put the formation energy of a pair of separated l- and D-defects at rather less than i eV. Experimental information from dielectric relaxation studies, which we shall discuss in chapter 9, gives a value of 0 68 eV which, in view of the uncertainties involved in the theory, represents reasonably satisfactory agreement. 

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