¹⁴N Nuclear Quadrupole Resonance in Ferroelectric Sodium Nitrite NaNO₂

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Nuclear quadrupole resonance has been studied in ferroelectric sodium nitrite (NaNO₂) from 77 K to its phase transition point 437 K. The three rotational frequencies ω_a=190 cm⁻¹, ω_b=120 cm⁻¹ and ω_c=227 cm⁻¹ and their temperature variation when fitted in the Bayer-Kushida theory predict the temperature dependence of nqr frequencies reasonably well. A second order phase transition is found to occur at 180 K which is in confirmity with the one found earlier from thermal expansion and dielectric studies. The shift in resonance frequencies is seen to occur mainly by rotation around the ‘c’ axis and hence it is inferred that the mechanism of polarization reversal is intimately connected with orientational motion about ‘c’ axis.