Electronic Structure of Colour Centres Theoretical Developments

Transport Atomique Et Thermodynamique Des Défautslattice Defects in Ionic Crystals

“…Such a formula follows from a generalised rate theory based on classical statistical mechanics; it would thus be expected to hold at high temperatures (T 9 (I,,) where the distributions of atomic positions and velocities conform to classical statistical mechanics. A number of examples exist where H' has been observed ( 4 ) Conipai-c c. g. the jump fi-equencies of free cation vacancies in alkali halides with thosc of cation \lacarlcics moving around divalent cation impi~rities in thc first co-ordiniition sliell [35]. These f o~~r terms thus add up to a gain of hetween i and 4 cV.…”

“…Although, in general, problenis do not divide as sharply as these two examples, it is convenient to order our remarks against these two parts of the problem. For the electronic part we can take Stoneham's review at the Reading Conference as our starting point [4], while for the lattice relaxation calculations the review by Lidiard and Norgett [ 5 ] dating from the same time will be found pertinent.…”

“…But this is also often far from being a good or allowable approximation, as in the case of defects bearing a net electric charge or having large elastic misfit (e. g. interstitials). For these defects there are various methods in use [4], [5], most notably (i) the Kanzaki Fourier transformation method (2), (ii) the Green's function method of Tewary and (iii) generalised Mott-Littleton methods. All three are in principle general methods but all detailed applications of the first two have so far involved particular assumptions about the symmetry of the defect, although the formulation by Stoneham and Bartram [59] allows the description of symmetry lowering via the Jahn-Teller effect.…”