Physics – Condensed Matter – Materials Science
Scientific paper
2007-03-06
Phys. Rev. B 76, 054125 (2007)
Physics
Condensed Matter
Materials Science
subm. to PRB, revised version according to referees' reports
Scientific paper
10.1103/PhysRevB.76.054125
Pb_1.83Mg_0.29Nb_1.71O_6.39 (PMN) crystallizing in a cubic pyrochlore structure exhibits, as the first dielectrics with pyrochlore structure, typical feature of quantum paraelectrics - its permittivity continuously increases on cooling and levels off below ~ 30K, without any signature of a structural phase transition. Broad-band dielectric spectra do not show any dielectric dispersion in the real part of permittivity up to 8.8 GHz. THz and infrared spectra reveal a soft polar optic mode which is responsible for the temperature dependence of the permittivity. The leveling-off of the permittivity at low temperatures obeys the Barrett formula and the fitted vibrational zero-point energy 1/(2*k_B*T_1) corresponds to the measured soft mode frequency. The number of observed infrared phonons exceeds that predicted from the factor-group analysis which indicates that the structure is at least locally non-cubic.
Bovtun Viktor
Denisov Sergey
Kalnberga M.
Kamba Stanislav
Nuzhnyy D.
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