An apparatus for the measurement of thermal expansion of solids at low temperatures

A dilatometer, using the three terminal capacitance technique, suitable for measurement of linear thermal expansion of solids in the temperature range 1.3-300 K is described. The dialtometer is designed such that the mounting system for the specimen does not undergo any significant changes in dimensions when the specimen is heated. The apparatus, therefore, yields in principle absolute values of α, the coefficient of linear thermal expansion. The performance of the apparatus has been checked by measurements on copper in the temperature range of 77-300 K. Some preliminary results on the behaviour of α for Y₁Ba₂Cu₃O_6.9 compound in the vicinity of superconducting transition temperature, T _c are also described. The system can detect relative changes in length Δl/l ₀ of about 10^-8. Attempts are being made to improve the sensitivity.