Linear birefringence studies of incommensurate systems: I. NaNO2

Abstract

Abstract The temperature dependence of the linear birefringences Δn b and Δn c of NaNO2 is measured in the temperature range 295 ≤ T ≤ 450 K. Discontinuities are found at the hysteretic lock-in transition into the ferroelectric state at T − c = 436.8 K and T + c = 437.1 K, respectively. Bending points characterize the onset of the incommensurate phase below T i = 438.6 K. Critical t 1-α and |t|β behavior is found above and below T i , respectively, where t = T/T i - 1. α = -0.02 ± 0.01 and β = 0.82 ± 0.02 are in accordance with the 3d XY-model. Anomalies of Δn c and of the low-frequency complex dielectric permittivity occur on heating around T + c . They are ascribed to the formation of domains in the ferroelectric regime, which subsequently give rise to a chaotic incommensurate phase.