A. V. Sotnikov

Giant dielectric relaxation in SrTiO3-SrMg1/3Nb2/3O3 and SrTiO3-SrSc1/2Ta1/2O3 solid solutions

Ceramic samples of (1−x)SrTiO3-xSrMg1/3Nb2/3O3 and (1−x)SrTiO3-xSrSc1/2Ta1/2O3 were prepared, and their dielectric properties were studied at x=0.005–0.15 and 0.01–0.1, respectively, at frequencies 10 Hz–1 MHz and at temperatures 4.2–350 K. A giant dielectric relaxation was observed in the temperature range 150–300 K, and not so strong but well-developed relaxation was found in the temperature range 20–90 K. The activation energy U and the relaxation time τ0 were determined to be 0.21–0.3 eV and from 10−11 to 10−12 s for the high-temperature relaxation and 0.01–0.02 eV and 10−8–10−10 s for the low-temperature relaxation, respectively. The additional local charge compensation of the heterovalent impurities Mg2+ and Nb5+ (or Sc3+ and Ta5+) by free charge carriers or the host ion vacancies is suggested to be the underlying physical mechanism of the relaxation phenomena. On the basis of this mechanism, the Maxwell-Wagner model and the model of reorienting dipole centers Mg2+ (or Sc3+) associated with the oxygen vacancy are proposed to explain the high-temperature relaxation with some arguments in favor of the latter model. The polaron-like model with the Nb5+-Ti3+ center is suggested as the origin of the low-temperature relaxation. The reasons for the absence of ferroelectric phase transitions in the solid solutions under study are also discussed.

Dielectric relaxation in SrTiO3–SrMg1/3Nb2/3O3 and SrTiO3–SrSc1/2Ta1/2O3 solid solutions

Dielectric properties of ceramic samples of (1−x)SrTiO3–xSrMg1/3Nb2/3O3 and (1−x)SrTiO3–xSrSc1/2Ta1/2O3 solid solutions were studied at x⩽15% and x⩽10%, respectively. The real and imaginary parts of the dielectric constant were measured at frequencies between 10 Hz and 1 MHz and in a temperature range of 4.2–300 K. Remarkable relaxation was found between 80 and 300 K. The relaxation was suggested to be due to local charge compensation processes. The activation energy for these processes was determined to be (0.25±0.05) eV with τ0=(10−12…10−13) s.

Dielectric relaxation in SrTiO3: Mn

Dielectric relaxation (activation energy U≈0.03 eV, relaxation time τ0≈5×10−11 s) has been observed in SrTiO3: Mn solid solutions at low temperatures. It is assumed that the relaxation is related to reorientation of the polarons localized at defects of the {MnTi2+-O−} type and that the deviations from classical thermally activated behavior at the lowest temperatures reached are due to the quantum tunneling mode.

Pyroelectric and elastic properties of lead magnesium niobate-and barium titanate-based solid solutions near a phase transition

The pyroelectric, elastic, and electrostrictive properties of lead magnesium niobate-and barium titanate-based solid solutions were studied under a dc electric field near a phase transition. The results obtained for a relaxor transition (in a lead magnesium scandium niobate solid solution) are compared with those derived for a conventional ferroelectric transition (in a barium strontium titanate solid solution). The dielectric and electromechanical contributions to the induced pyroelectric effect are discussed.

Pyroelectric effect in lead-magnoniobate-based solid solutions

A coordinated study of the dielectric, electrostriction, and pyroelectric properties of the lead-magnoniobate-based ceramic solid solutions 0.9PbMg1/3Nb2/3O3-0.1PbTiO3 and 0.55PbMg1/3Nb2/3O3-0.45PbSc1/2Nb1/2O3 conducted at the relaxor transition temperatures is reported. Electromechanical coupling stimulated by the giant electrostriction effect is shown to play an essential part in the pyroelectric effect.

Evolution of phase transitions in SrTiO3-BiFeO3 solid solutions

The dielectric and acoustic properties of (1 − x)SrTiO3−xBiFeO3 solid solutions (0 ≤ x ≤ 1) have been studied in the temperature range from 4.2 to 850 K. Evolution of the antiferrodistortive transition and its suppression in the concentration range 0.1 < x < 0.2 have been revealed. X-ray diffraction data obtained at room temperature, as well as the observed acoustic anomalies combined with dielectric measurements, have been used to estimate the concentration range of the existence of the relaxor state, as well as of the formation and coexistence of the antiferromagnetic and ferroelectric phases at high BiFeO3 concentrations.

Dielectric properties of solid solutions PbMg1/3Nb2/3O3-SrTiO3

Ceramic samples of the solid solutions PbMg1/3Nb2/3O3-SrTiO3 are synthesized. The dielectric properties are studied and a phase diagram is constructed. The results obtained are discussed in terms of ideas concerning relaxor ferroelectrics for solid solutions on the PMN side and from the standpoint of potential ferroelectrics on the SrTiO3 side. The introduction of SrTiO3 into PMN gradually degrades relaxor properties, and the introduction of PMN into SrTiO3 does not result in initiation of the ferroelectric phase transition, possibly because of the appearance of random fields in the lattice. The possibility of practical applications of the synthesized system is also discussed.

Relaxor behavior of SrTiO3-LiNbO3 solid solutions

Ceramic samples of (1 − x)SrTiO3-xLiNbO3 (0 ≤ x ≤ 0.05) solid solutions are synthesized. The dielectric and acoustic properties of the solid solutions are studied in the temperature range from 15 to 300 K. It is revealed that the polar state characterized by the dispersion of the permittivity and the dielectric hysteresis occurs at low temperatures. The results obtained are discussed within the concept of relaxor ferroelectrics.

Phase transitions and dielectric relaxation in (1 − x)SrTiO3-xBiFeO3 (0 ≤ x ≤ 0.04)

The dielectric and acoustic properties of (1 − x)SrTiO3-xBiFeO3 (0 ≤ x ≤ 0.04) solid solutions have been studied in the temperature range 10–300 K. The polar state exhibiting permittivity dispersion and dielectric hysteresis loops has been revealed at temperatures of 40–100 K. At 20–40 K, we have observed one more dielectric relaxation, which is not associated with the polar state and vanishes at a concentration of the second solid-solution component x = 0.04. The antiferrodistorsive transition has been found to vary with increasing concentration x. At temperatures below the antiferrodistorsive transition point, the polar (relaxor) state has been shown to persist in all the measured solid solutions.

Piezĭlectric and elastic properties of Sr3NbGa3Si2O14 (SNGS) single crystals

The elastic, piezoelectric, and dielectric constants of new piezoelectric single crystals Sr3NbGa3Si2O14 (SNGS) are measured. The elastic moduli C11 and C66 and the piezoelectric coefficient e11 are determined over a wide temperature range. It is demonstrated that the piezoelectric activity of the crystal is retained up to the highest temperatures (900°C).