Microhardness and Schottky defects in alkali halides

Abstract

A simple relation between microhardness HV and the energy of formation WS of Schottky defects in alkali halides is developed. Microhardness HV is calculated from the known values of WS for all the alkali halides.

Systematic hardness measurements on single crystals and polycrystalline blanks of cesium halides

“…The constant in the equation arises out of the work done by the indenter in displacing crystalline matter and the volume per vacancy pair, both of which are dependent on the structure of the crystal. Shukla and Bansigir (1976) obtained a linear plot between H V and the parameter E f /r 3 in accordance with (4). They did not include the cesium halides in their analysis.…”

“…All data points lie on a straight line except the data point for the Harshaw Catalogue value for CsI. Shukla and Bansigir (1976) proposed a model according to which the indentation made during a hardness measurement on an ionic crystal results in the creation of a certain number of Schottky defects. For a crystal with NaCl structure, they obtained the relation…”

Temperature dependence of microhardness in mixed crystals

“…The microhardness (Hv) of binary ionic solids is related to the Schotky defect formation energy (w~) as (Shukla and Bansigir 1976)…”

“…One well-known property is microhardness, which for mixed crystals always exceeds its value for the component crystals (Armington et al 1973;Hari Babu et al 1975). A number of theories (Gilman 1973;Shukla and Bansigir 1976;Boser 1972;Ridhagani and Asimow 1968) have been proposed to explain this extra hardness of mixed crystals. Earlier theories of Gilman (1973) and Shukla and Bansigir (1976) could not explain the microhardness of mixed crystals as indicated by Bhimshankaran (1974), andSrivastava (1980).…”

“…A number of theories (Gilman 1973;Shukla and Bansigir 1976;Boser 1972;Ridhagani and Asimow 1968) have been proposed to explain this extra hardness of mixed crystals. Earlier theories of Gilman (1973) and Shukla and Bansigir (1976) could not explain the microhardness of mixed crystals as indicated by Bhimshankaran (1974), andSrivastava (1980). Kataoka and Yamada (1977) have given a theory according to which the random distribution of doped ions can produce an internal stress field interaction that increases the microhardness of the mixed crystals.…”