²³Na Nuclear-Magnetic-Resonance Study of the Ferroelectric Transition in Silver Sodium Dinitrite, AgNa(NO₂)₂

Abstract

The central NMR spectrum of ²³Na in the ferroelectric silver sodium dinitrite (AgNa(NO₂)₂) is investigated. The second-order quadrupolar-shifts in the single crystals are measured. The rotation patterns about the three crystalline axes in the paraelectric and the ferroelectric phases are analysed by Volkoff method. For the calculation of the EFG, the chemical shift of ²³Na ions as well as the distribution in the EFG must be taken into account. The ²³Na EFG tensors in a unit cell of AgNa(NO₂)₂ are identical in the paraelectric phase. They split into the two kinds of EFG whose principal components are equal in magnitude and differ only in the orientation of the principal axes. The powdered samples show that nonstoichiometry does not affect the electric field gradient seriously. The temperature dependence of the EFG tensor is discussed in comparison with that of NaNO₂.