The design and construction of an automatic capacitance dilatometer and its use at low temperatures

An apparatus to measure linear thermal expansion of various specimens using three terminal capacitance technique has been designed and constructed. The measurement is controlled by a DAI microcomputer through an industrial rack interface which monitors all aspects of the experimental control and measurement over a 3–4 days period required for each experiment. All interfaces were "in house" designed and built and all control software was custom designed. Early experiments using an adapted Michelson interferometer method confirmed that the three terminal capacitance dilatometer can be used with confidence under specific experimental conditions and suitable guidelines were produced for their use. The apparatus has been used to measure the thermal expansion of several materials including Cr-doped GaAs and amorphous arsenic.