Expansion coefficients of structural materials at low temperatures

1968 ◽  
Vol 10 (4) ◽  
pp. 267-269 ◽  
Author(s):  
A. K. Belov
Keyword(s):  
Low Temperatures ◽  
Structural Materials ◽  
Expansion Coefficients

The thermal expansion of alkali halides at low temperatures

1965 ◽  
Vol 286 (1405) ◽  
pp. 204-217 ◽  
Keyword(s):  
Low Temperatures ◽  
Room Temperature ◽  
Alkali Halides ◽  
Theoretical Models ◽  
Liquid Oxygen ◽  
Rock Salt Structure ◽  
General Behaviour ◽  
A Value ◽  
Salt Structure ◽  
Expansion Coefficients

Linear thermal expansions of eight alkali halides have been determined at liquid oxygen temperatures and at temperatures from 30 °K down to 2 °K. For temperatures T ≤ θ/20, where θ is the Debye temperature, the expansion coefficients are well represented by α = AT 3 + BT 5 . Values are reported for the Grüneisen parameter γ = 3α V/Cx , where C/V is the heat capacity per unit volume and x is the compressibility. For CsBr (b.c.c. structure) γ appears to be nearly independent of temperature, with a value of 2·0 but for the other crystals, which have the rock-salt structure, the parameter γ varies with temperature, chiefly betw een θ/10 and θ/5. At room temperature, γ lies between 1·45 and 1·7 but at low temperature this generally decreases to a value γ 0 which is ca. —0·1 for RbI, +0·3 for KCl, KBr and KI and 1·0 for NaCl and Nal; LiF does not show this decrease, γ 0 being 1·7. The values observed for γ 0 are compared with those calculated from elastic constants and their pressure derivatives and the general behaviour of γ( T ) is observed to conform qualitatively to the predictions of simple theoretical models of Born, Blackman and Barron.

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