The Electric Field Gradients at the Sites of 23Na in Ferroelectric AgNa(NO2)2

Abstract

Electric field gradients (EFG) at Na sites in ferroelectric AgNa(NO 2 ) 2 have been calculated on the basis of a point charge model. The electric charge distribution in N and O atoms in NO 2 molecules was calculated by assuming perfect ionicity of AgNa(NO 2 ) 2 crystal. Crystallographic positions for A and B sites of the EFG in the ferroelectric phase have been assigned by a lattice sum. By representing the charge of NO 2 - ion by a point charge – e at the middle point of O-O line, the largest component of the EFG tensor of fictitious perfectly ordered state (\(\varPhi_{xx}^{D}(T)\)) and that of the fictitious disordered state (\(\varPhi_{xx}^{\text{D}}(T)\)) have been calculated as functions of temperature. The observed EFG is represented fairly well by the relation \(\varPhi_{xx}^{\text{ob}}(T){=}\varPhi_{xx}^{\text{D}}(T)+(\varPhi_{xx}^{\text{O}}(T)-\varPhi_{xx}^{\text{D}}(T))S(T). \)