Formation enthalpy of schottky defects in alkali halide crystals and of anti-Frenkel defects in CaF2-type crystals

Abstract

on the occasion of his 75th birthday The formation enthalpy hs of Schottky defects in alkali halide crystals is related to the heat L and temperature T, of fusion: hs == 8 L/NA (NA Avogadro constant) with L = (0.0352 K-l T, -11) kJ/mol. This means that the vacancy mechanism governs the melting process of alkali halides. The formation entropy $5 of Schottky defects is given by BQ = (2 to 3) s , ( 8 , entropy of fusion). The formation enthalpy ~A F of anti-Frenkel defects in MeX2 crystals of fluoritetype (Me metal; X halogen, oxygen) depends on the heat L of fusion, too: ~A F = 1.37 eV +-Die Bildungsenthalpie hs der Schottky-Defekte in Alkalihalogenidkristallen steht in direktem Zusammenhang mit der Schmelzwiirme L und der Schmelztemperatur T,: hs = 8 L / N A (NA Avogadro-Konstante) mit L = (0,0352 K-l T, -11) kJ/mol. Das bedentet, da13 das Schmel-Zen der Alkalihalogenide durch den Leerstellenmechanismus bestimmt wird. Die Bildungsentropie ss der Schottky-Defekte ist ss = (2 bis 3) s , ( 8 , Schmelzentropie). Die Bildungsenthalpie ~A B der Anti-Frenkel-Defekte in MeX,-Kristallen vom Fluorit-Typ (Me Metal1 ; X Halogen, Sauerstoff) ist ebenfalls proportional zu L: ~A F = 1,37 eV + 3,44 L / N A .-+ 3.44 L/NA.

Microhardness of mixed silver halides

“…The theory described above has been used to calculate the microhardness of AgCl-AgBr mixed crystals. The microhardness of the host silver halides have been obtained from the formation enthalpy of point defects as expressed by Bollmann (1980) W, = 0.0829 L .…”

“…Here, L is the heat of fusion, whose values are taken from Bollmann (1980). The heat of fusion can be correlated to the microhardness of single crystals through the relation:…”

“…This adequacy of Kataoka and Yamada's theory seems to be primarily because it takes proper account of plastic deformation and the internal stress field of elastic interactions in the mixed crystals. (Bollmann 1980)…”

Formation Volume of Schottky Defects (Vacancies) in Inorganic and Organic Compounds and the Defect Formation Mechanism of Melting

“…The idea that the formation of vacancies within a crystal is a kind of pre-melting led to the following relation between the formation enthalpy hs of Schottky defects and the heat L of fusion (BOLLMANN 1980):…”