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Abstract
Thiourea SC(NH2)2 is a typical crystal which has many incommensurate phases. Phase transitions of thiourea have been studied by many workers. Thier temperature dependences of Brillouin scattering spectra have been studied in detail. Following results were obtained (1) frequency shifts Δv of TA-mode(C66) showed a small bend at Ti and a small jump at Tc' (2) Δv of LA-mode (C11) had a small jump at Ti and bends at T8 (modulation wave number δ= 1/8) and Tc Integrated intensities of each spectra exhibited various anomalies.