Ultrasonic Relaxation near the Curie Temperature of Ferroelectric Triglycine Sulfate

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Abstract
According to a theory developed by Landau and Khalatnikov, the approach of long‐range order to equilibrium can be characterized by a relaxation time with a temperature dependence of the form: τ=β/(Tc − T), where β is constant and Tc is a second‐order phase transitiontemperature. The ferroelectric material, triglycine sulfate, is known to undergo a second‐order phase transition at its Curie temperature. The long‐range order is identifiable with the spontaneous polarization directed along the crystallographic B axis. Ultrasonic waves traveling perpendicularly to the B axis coupled to the spontaneous polarization and exhibited marked relaxational effects for TTc . These domains, which point along the B axis, have cross sections comparable in size to the sound wavelengths.

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