Dilatometry under high pressure

Abstract

In order to measure anisotropic compressibilities and thermal expansion of cubic, tetragonal or orthorhombic single crystals under pressure we have miniaturized a high resolution capacitive dilatometer and integrated this device in a high pressure cell within a cryostat which allows a temperature variation from 10 K to 320 K. To minimize the number of electrical lead-throughs from ambient pressure to the high pressure volume we did not use the three terminal method but used the dilatometer type of Meingast et al. [1]. The electrical lead-through of the triaxial cable was realized by using a double Bridgman cone-type lead-through. One of the two capacitance plates is fixed. The other plate is connected to a piston which is mounted with a parallel spring suspension to enable a parallel and frictionless motion of the piston and the capacitor plate. Length changes of a sample are transferred to the piston which enables a high resolution measurement of length changes by monitoring the capacitance changes. Length changes of about ΔL/L = 10⁻⁸ can be resolved for a typical sample length of 1 mm.

Key Words:

• High pressure techniques
• thermal expansion
• compressibility
• phase transformations
• glass transitions