E.N. Sidorenko - Ph.D. (Phys.-Math.), Associate Professor, Southern Federal University. E-mail: si-do-re@mail.ru, ensidorenko@sfedu.rsu.ru V.G. Gavrilyatchenko - D.Sc. (Phys.-Math.), Professor, Southern Federal University. E-mail: gavrilyatchvg@sfedu. ru A.V. Turik - D.Sc. (Phys.-Math.), Professor, Southern Federal University. E-mail: turik@phys.rsu.ru A.F. Semenchev - Ph.D. (Phys.-Math.), Associate Professor, Southern Federal University. E-mail: aleksasha@ phys.rsu.ru I.I. Natkhin - Assistant, Southern Federal University

The absorption spectra of UHF energy in ferroelectric crystals BaTiO3 and PbTiO3 were studied in the frequency range of 7.8-11.5 GHz. The measurement setup included panoramic VSWR/attenuation meter and sweep generator with miniature broadband microstrip line specially fabricated as a measuring cell. When studying the absorption spectra of the crystals with different domain structure, it was observed that, as a rule, the absorption of energy was uniform in the whole frequency range within the level of ?(3-10) dB. For the case when on the edges of central conductor of the microstrip line the crystals of PbTiO3 were placed which had complex domain structure with predominating groups of small а- and с-domain wedge-like twins oriented with respect to the several twinning systems within each group, the spectra featured sharp narrowband absorption maxima of resonant type of about ?(20-40) dB. The absorption increased more when the crystal was preliminary polarized by constant electric field for which the 90° domain structure is not destroyed yet. With the growth of temperature, the frequency of the absorption peak moved with respect to its room-temperature position at first to higher frequencies by ~250 MHz, and then, starting from T = 60-70°C it moved to the region of lower frequencies by more than 1 GHz. With crystal heating, the level of energy absorption in the peak at first increased down to - 40 dB, and then it decreased up to -20 dB at T = 70-80°C, and in the vicinity of Curie point, at which the domain structure is the most labile, the loss again increased up to - 35 dB. After completion of phase transition in paraelectric phase resonant peaks practically disappeared in an absorption spectrum. The presence of resonant-type loss maxima in BaTiO3 crystals is probably due to piezoelectric oscillations of both с- and а-domain wedges. Nonmonotonic dependence of resonant frequency on temperature can be attributed to peculiarities of temperature variations of dielectric permittivity and elastic compliance tensor components of BaTiO3 crystal in tetragonal ferroelectric phase. The obtained experimental results witness the presence of a resonant contribution to dielectric UHF dispersion of BaTiO3 crystals. For PbTiO3 crystals which exhibit the domain structure similar to that of BaTiO3, the strong absorption of UHF energy is not observed due to the high stiffness of domain structure.

 

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