Linear Thermal Expansion Coefficient of the NaCl Phase of CsCl

The linear thermal-expansion coefficient of the lowtemperature phase of CsCl, alpha (T) = DELTA l/l(T) DELTA T, where T is the average temperature in the interval DELTA T, was determined to be 4.78 x 10/sup -5/ (C deg )/sup -1/ between 50 and 150 deg C. The average expansion coefficient between 570 and 590 deg C in the NaCl phase was 5.1 x 10/sup -5/ (C deg )/sup -1/ with an estimated error of 10% based on the reproducibility. Just below the phase change the lattice parameter expansion coefficient is 6.6 x 10/sup -5/ (C deg )/sup -1/ and the NaCl phase is seen to have a lower expansion coefficient than the more closely packed CsCl phase. (P.C.H.)