Determination of the Low-Frequency Electro-optic Coefficients of NaNO2

Abstract

The unclamped electro‐optic coefficients were measured in ferroelectric NaNO₂. The following values were obtained at 150°C, in units of 10⁻¹⁰ cm/V: r_a = r₂₂ − (n₃/n₂)³r₃₂ = 4.1; r_b = r₃₂ − (n₁/n₃)³r₁₂ = 4.2; r_c = r₂₂ − (n₁/n₂)³r₁₂ = 0.6; r₄₃ = − 1.9; r₆₁ = − 3.0. The constants r_a and r_c vary approximately as ε₂ does near the Curie temperature, as expected, but r_b does not, decreasing toward zero at T_c. No significant temperature dependence was found in r₆₁ or r₄₃. The quantity r_a changes sign as a function of temperature at 115°C. The observed behavior can be explained in terms of a temperature‐independent response including both second‐ and fourth‐order terms, biased by the spontaneous polarization.