Miniature torsion pendulum for studying the phase transition in ferroelastic crystals

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Abstract
Describes a miniature torsion pendulum and an electronic setup for generation and detection of its resonance torsional vibration at constant amplitude. The regenerative feedback loop based on a pi /2 phase shifter maintains the system at resonance although the resonant frequency may change several times during the course of an experiment. The apparatus allows one to measure continuously shear modulus and internal friction of crystalline samples cut out as rectangles with dimensions of the order of millimetres. Using the apparatus described, the temperature dependence of shear modulus G1 and internal friction Q-1 for a sample cut out from LiCsSO4 ferroelastic crystal were measured.