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Theory of the Order Parameter of NaNO 2 in Molecular Field Approximation
Author(s) -
Bonilla I. R.,
Holz A.,
Rutt H. N.
Publication year - 1974
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220630129
Subject(s) - dipole , ion , condensed matter physics , phase transition , physics , electric field , coulomb , lattice constant , electric dipole moment , dielectric , mean field theory , quantum mechanics , diffraction , electron
A static theory of the order‐disorder, ferro‐paraelectric phase transition in NaNO 2 is developed. The Coulomb energy of the system is calculated in the point charge approximation. The model takes the relative displacement δ°( T ) of the Na + ions from their symmetrical position as a function of temperature into account; and the strong correlation of the Na + ion position with the dipole orientation of the neighboring NO 2 − ion. The short range force potential acting on the Na + ion is fitted by means of δ°(0) which can be taken from experiment. The long‐range order parameter Ω is calculated in the molecular field approximation. A first order phase transition is obtained for which the critical values T c and Ω c are calculated as a function of the permanent electric dipole moment of NO 2 − and δ°(0). Only qualitative agreement with experimental results is obtained. The Made‐lung constant of the lattice is obtained as α = 1.93.