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Quantum paraelectric behavior of pyrochlore PMN

S. Kamba·D. Nuzhnyy·S. Denisov·S. Veljko·V. Bovtun·M. Savinov·J. Petzelt·M. Kalnberga·A. Sternberg
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Abstract

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.

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S. Kamba, D. Nuzhnyy, S. Denisov, S. Veljko, V. Bovtun, M. Savinov, J. Petzelt, M. Kalnberga, A. Sternberg. 2007-07-12. Quantum paraelectric behavior of pyrochlore PMN. https://doi.org/10.1103/physrevb.76.054125

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