V. I. Zinenkoa, N. G. Zamkovaa, E. G. Maksimovb, and S. N. Sofronovaa
a Kirensky Institute of Physics, Siberian Division, Russian Academy of Sciences, Krasnoyarsk, 660036 Russia
b Lebedev Physical Institute, Russian Academy of Sciences, Moscow, 119991 Russia
e-mail: maksimov@lpi.ru
Received March 28, 2007
Abstract—The dynamic Born charges and the frequency spectra of lattice oscillations in the crystals of ordered
and disordered PbSc1/2Ta1/2O3 (PST) and PbSc1/2Nb1/2O3 (PSN) solid solutions have been calculated within the
framework of the generalized Gordon–Kim model with allowance for the dipole and quadrupole polarizabili-
ties. The phonon spectra of both compounds contain ferroelectric soft modes. The influence of various interac-
tions on the magnitude of dynamic charges and ferroelectric instability in PSN and PST solid solutions has been
studied and it is shown that both these charges and the ferroelectric instability are determined by the competi-
tion between long-range dipole–dipole interactions and short-range dipole–charge interactions, the determining
role played by the interaction of Nb (Ta) cations and oxygen anions in the Nb–O (Ta–O) bond direction.
PACS numbers: 61.50.Ah, 63.20.Dj, 71.15.Mb
DOI: 10.1134/S1063776107090191
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