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In situ temperature-dependent Raman-scattering experiments under an external dc electric field E have been performed on (1 − x)Na 0.5 Bi 0.5 TiO 3 - x BaTiO 3 single crystals with x ranging from 0.013 to 0.074 in order to gain further insights into the atomistic mechanism of polar coupling in lead-free perovskite-type (ABO 3) ferroelectric solid solutions near the morphotropic phase boundary (MPB). The polarized Raman spectra collected between 770 and 100 K under an E applied along the pseudocubic [100] direction were analyzed in terms of hard-mode spectroscopy. The results reveal enhanced coupling between the polar displacements of the A-site Bi 3 + and B-site Ti 4 + cations for x = 0.048 ∼ x M P B when a moderate E [ 100 ] field is applied, a local-scale phenomenon that might be responsible for the known drift of the MPB under external stimuli. In addition, for all studied compounds, the characteristic temperatures T A − A ′ and T A − A ′ ′ , preceding the macroscopic T m and T d and related to mesoscopic-scale antiferroelectric and ferroelectric coupling processes within the A-site-cation subsystem in a zero field, merge into one even under a weak electric field, suggesting that the structural state between the paraelectric and ferroelectric zones in the x -T diagram is weak ferrielectric. [ABSTRACT FROM AUTHOR]

PbSc0.5Ta0.36Nb0.14O3 relaxor ferroelectrics crystals were investigated in a wide temperature range of 200-700K using acoustic emission. The intermediate temperature T* as well as the Burns temperature Td were successfully detected at 480K and 581 K, respectively. Another acoustic emission burst was detected at Tnl ~211K, which is below the temperature of the dielectric-permittivity maximum Tnl ~257K but it is accompanied by a slight anomaly in the dielectric permittivity. Tnl is attributed to the low-temperature boundary of an incommensurately modulated antiferroelectric phase transition taking place over a temperature range. All characteristic temperatures exhibit frequency dispersion in the range of 0.1-10 kHz, which is considerably stronger for T* and Td than for Tm and Tnl . In addition, Tnl depends linearly on frequency, whereas both T* and Td resemble the non-linear frequency dependence of Tm typical of relaxors. The nature of the frequency dispersion of T* and Td is discussed from the viewpoint of complex behavior of low-energy polar modes intrinsic of relaxor ferroelectrics. [ABSTRACT FROM AUTHOR]

The behavior of the temperature of the dielectric-permittivity maximum Tm, the intermediate temperature T*, and the Burns temperature Td in stoichiometric PbSc0.5Nb0.5O3 (PSN) as well as in PSN heavily doped on the A-site by La (PSN-La), Ba (PSN-Ba), and Sr (PSN-Sr) was studied by means of acoustic emission (AE) under an external dc electric field (E). For all compounds, Tm exhibits a non-trivial behavior when applying E, namely, it initially decreases with the increase of E, attain a minimum at a threshold field Eth, ranging from 0.55 kV/cm for PSN to 0.25 kV/cm for PSN-Sr, and then Tm starts to increase with further increase of E. The minimum of Tm is accompanied by a pronounced maximum of the AE count rate N, which at Eth varies from 10.0 s-1 to 3.0 s-1 for all the compounds, respectively. The similarities and difference between PSN, PSN-Ba, PSN-La, and PSN-Sr with respect to Eth, the N, and the normalized AE parameter η are discussed from the viewpoint of three mechanisms: (i) chemically induced random local electric fields due to the extra charge on the A-site ion, (ii) disturbance of the system of stereochemically active lone-pair electrons of Pb2+ by the isotropic outermost electron shell of the substituting ion, and (iii) change in the tolerance factor and elastic fields related to the larger ionic radius of the substituting A-site ion. The characteristic temperatures T* and Td also exhibit a non-trivial behavior under E, which is better pronounced for pure PSN than for the A-site-substituted PSN compounds. [ABSTRACT FROM AUTHOR]

In situ temperature-dependent Raman-scattering experiments under an external dc electric field E have been performed on PbSc0.5Ta0.5O3 (PST) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (PST-Ba) in order to give further insights into the atomistic mechanism of polar coupling in perovskite-type (ABO3) relaxor ferroelectrics near the intermediate characteristic temperature T*. The polarized Raman spectra collected under an electric field E applied along the cubic [100], [110], or [111] crystallographic direction were analyzed in terms of hard-mode spectroscopy. The T*(E) dependence was derived from the behavior of the phonon mode near 230 cm-1 localized in off-centered B-site cations. In the case of stoichiometric PST, the increase of T* with E is much stronger when the field is applied along [111] than when E is along [100] or [110]. This indicates that the actual polar B-cation shifts are along the cubic body diagonals, implying a rhombohedral structure of the polar nanoregions. The T*(E)-dependence reveals that the local structural distortions associated with locally coupled polar displacements of B-site cations reach saturation near 0.5 kV/cm. When Pb2+ is partially replaced by Ba2+, the strong increase of T* with E occurs if the electric field is applied along the [110] direction. This indicates that the substitution disorder on the A-site lowers the symmetry of the polar nanoregions to orthorhombic or monoclinic. The T*(E) dependence determined from the B-cation localized mode shows saturation near 2.0 kV/cm, indicating that the zero-field structural state of PST-Ba exhibits less coupled polar shifts of B-site cations as compared to that of PST. According to the E-dependence of the Raman scattering near 55 cm-1, for both compounds the overall response of the Pb system to the external electric field in the vicinity of T*(E) resembles antiferroelectric behavior, which along with the fact that the coupling between the B-site cations is ferroelectric, suggests that the polar nanoregions in Pb-based relaxors are ferrielectric in nature. [ABSTRACT FROM AUTHOR]

The effect of the type of B-site substituent on the development of the ferroelectric state in the tetragonal part of the composition-temperature (x-T) diagram of (1-x)PbTiO3-xBi B 0.5 ′ B 0.5 ″ O3 solid solutions is analyzed by applying the second harmonic generation (SHG) method and Raman spectroscopy to three compounds with B 0.5 ′ B 0.5 ″ = Mg0.5Ti0.5, Ni0.5Ti0.5, and Ni0.5Zr0.5, having nearly the same tolerance factor and unit-cell tetragonality, at temperatures up to ∼1000 K. The results reveal the importance of B-site divalent dopants with an isotropic electron configuration for the enhancement of local symmetry breaking at the A site and a consequent increase in the Curie temperature at small x, regardless of the macroscopic tetragonality with respect to PbTiO3. [ABSTRACT FROM AUTHOR]

The structural transitions in Pb1-xLaxSc(1+x)/2Ta(1-x)/2O3, x = 0.08 (PLST) relaxor crystals were studied by means of acoustic emission (AE) under an external electric field (E) and compared with those observed in pure PbSc0.5Ta0.5O3 (PST) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (PBST) [E. Dul'kin et al., EPL 94, 57002 (2011)]. Similar to both the PST and PBST compounds, in zero field PLST exhibits AE corresponding to a para-to-antiferroelectric incommensurate phase transition at Tn = 276 K, lying in the vicinity of dielectric temperature maximum (Tm). This AE signal exhibits a nontrivial behavior when applying E resembling the electric-field-dependence of Tn previously observed for both the PST and PBST, namely, Tn initially decreases with the increase of E, attains a minimum at a threshold field Eth = 0.5 kV/cm, accompanied by a pronounced maximum of the AE count rate N = 12 s-1, and then starts increasing as E enhances. The similarities and difference between PST, PLST, and PBST with respect to Tn, Eth, and N are discussed from the viewpoint of three mechanisms: (i) chemically induced random local electric field due to the extra charge on the A-site ion, (ii) disturbance of the system of stereochemically active lone-pair electrons of Pb2+ by the isotropic outermost electron shell of substituting ion, and (iii) change in the tolerance factor and elastic field to the larger ionic radius of the substituting A-site ion due to the different radius of the substituting ion. The first two mechanisms influence the actual values of Tn and Eth, whereas the latter is shown to affect the normalized N, indicating the fractions undergoing a field-induced crossover from a modulated antiferroelectric to a ferroelectric state. Creation of secondary random electric field, caused by doping-induced A-site-O ionic chemical bonding, is discussed. [ABSTRACT FROM AUTHOR]

Using atomic force microscopy and piezoresponse force microscopy (PFM), as well as complementary dielectric measurements, the ferroelectric domain structure of single crystals of pure and ruthenium (Ru)-doped 0.9Pb(Zn1/3Nb2/3)O3 (PZN)-0.1PbTiO3 (PT), and Ru/(Zn+Nb+Ti)∼0.002 was analyzed. The coexistence of tetragonal and nontetragonal ferroelectric domains in PZN-PT near the morphotropic phase boundary (MPB) was directly observed via PFM imaging. The incorporation of Ru in the perovskite structure substantially decreases the ferroelectric domain size, thus reducing the polar fraction distributed in the pseudocubic matrix. The polarization and strain hysteresis loops show that Ru doping leads to significant ferroelectric hardening, which is attractive for high-power applications. The local structure and valent state of the incorporated Ru cations were additionally analyzed by electron paramagnetic resonance spectroscopy. Our results demonstrate that doping of tetragonal PZN-PT near MPB is a promising route to design advanced multifunctional single-crystal materials. [ABSTRACT FROM AUTHOR]

The crystallization process of colloidal (nanosized) molecular sieves stabilized in water with Raman and (super 13)C NMR spectroscopic methods was investigated by using the encapsulation of small quaternary ammonium ions in zeolite framework. The molecular packing effect and restricted mobility resulted in the shifts and substantial broadening of the (super 13)C NMR signals and, position changes and relative intensities of the Raman peaks.

The in-situ incorporation and characterization of 2-(2'-hydroxyphenyl)benzothiale (HBT) in the cages of nanosized FAU zeolites is reported. The spectroscopic data reveal that the HBT molecules are incorporated in the nanosized zeolite particles leading to changes in the environment of the tetramethylammonium hydroxide (TMA) ions as well as in the local atomic arrangements of the FAU structure.

The local structure and atomic dynamics of (1-x)Na0.5Bi0.5TiO3-xBaTiO3 with x ranging from 0 to 0.074 were analyzed at room temperature by in situ single-crystal Raman spectroscopy under an external dc electric field E applied along the pseudocubic [100]c or [110]c directions, to gain further insights into the atomistic mechanism of polar coupling near the morphotropic phase boundary (MPB). The results reveal a striking compositional dependence of the E [ 100 ] c -induced changes in the Raman scattering and suggest that the origin of the enhanced longitudinal piezoelectric coefficient in alkali-Bi based solid solutions with a pseudocubic structure near MPB is due to the composition-driven reduction of the local strains and the consequent enhancement of the structural flexibility under external stimuli. [ABSTRACT FROM AUTHOR]