Brillouin scattering of the order-disorder type phase transition in NaNO 3

Abstract

NaNO 3 undergoes the order-disorder type phase transition with the anti-parallel order of NO 3 molecules along the three-fold z axis at T c = 276.5°C. A Brillouin scattering experiment was performed to observe the c 33 pure longitudinal acoustic mode coupled with the fluctuation of the anti-parallel order in the temperature range between 23.22°C and 299.55°C. The relaxation time of the fluctuation was determined as a function of temperature below T c to be τ f/( T c − T), where τ fis(6.0 ± 0.7) × 10 −11s deg. τ f is one order lower than the previous result reported by the ultrasonic study.