Optical and acoustic properties of 33PbIn1/2Nb1/2O3-35PbMg1/3Nb2/3O3-32PbTiO3 single crystals in an electric field

The influence of different conditions of applying a dc electric field (0 < E < 4 kV/cm) on the behavior of optical transmission and on the acoustic parameters (sound velocity and attenuation) in the [001]- and [011]-oriented single crystals 33Pb(In_1/2Nb_1/2)O₃-35PbMg_1/3Nb_2/3O₃-32PbTiO₃ existing near the morphotropic phase boundary has been investigated. It has been found that the optical transmission, sound velocity, and attenuation sharply change near the phase transition in a narrow range of electric fields for any method of their applying. In the field applied along [001], the change in the sound velocity due to the phase transition is 1.5 times greater than that in the field applied along [011]. This is caused by a larger contribution of the piezoelectric effect to the elastic modulus determining the sound velocity along [001] as compared to [011]. It has been shown that the number, symmetry, and stability of the phases formed in the field depend on the conditions of applying the field.     

Effect of electric field on the smeared phase transition in crystals PbIn1/2Nb1/2O3-28PbTiO3 and PbIn1/2Nb1/2O3-37PbTiO3

The effect of a direct-current electric field (0 < E < 3 kV/cm) on the smearing of the phase transition and the Curie-Weiss exponent (γ) for two PbIn_1/2Nb_1/2O₃-28PbTiO₃ and PbIn_1/2Nb_1/2O₃-37PbTiO₃ crystals lying at different distances from the morphotropic phase boundary has been investigated. The universal Curie-Weiss law has been used to approximate the temperature dependences of the dielectric permittivity. It has been shown that the more remote is the crystal from the morphotropic phase boundary, the larger is the exponent γ and, consequently, the more smeared is the phase transition (in the zero field, γ = 1.67 and 1.49 for PbIn_1/2Nb_1/2O₃-28PbTiO₃ and PbIn_1/2Nb_1/2O₃-37PbTiO₃, respectively). It has been found that a weak electric field (no greater than 2–3 kV/cm) in the case of the more smeared phase transition almost does not affect the Curie-Weiss exponent, whereas for the PbIn_1/2Nb_1/2O₃-37PbTiO₃ crystal, this exponent decreases with increasing electric field strength and approaches γ = 1, which is characteristic of the conventional ferroelectric.     

Evolution of dielectric and optical properties in PbIn1/2Nb1/2O3-PbMg1/3Nb2/3O3-PbTiO3 single crystals in an electric field

A study is reported of various modes of dc electric field application (0 < E < 3 kV/cm) on structural phase transformations and behavior of the phase boundary in [001]-oriented 30PbIn_1/2Nb_1/2O₃-37PbMg_1/3Nb_2/3O₃-33PbTiO₃ single crystals located close to the morphotropic phase boundary. Dielectric methods of investigation have been complemented for the first time with optical methods. It has been found that the number, symmetry, and stability of the phases formed in the field depend on the actual mode of field application. The E-T phase diagrams have been constructed for different field application modes. It has been shown that phase diagrams obtained for the same crystal are different for different field application modes.     

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

Ceramic samples of the solid solutions PbMg_1/3Nb_2/3O₃-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. Fiz. Tverd. Tela (St. Petersburg) 41, 1091–1095 (June 1999)     

Optical and dielectric anomalies in PbIn1/2Nb1/2O3-xPbTiO3 crystals in an electric field

A study is reported of the effect produced by application of a dc electric field (0 < E < 5 kV/cm) in different regimes on structural phase transformations and behavior of the phase boundary in [001]-oriented PbIn_1/2Nb_1/2O₃-37PbTiO₃ single crystals (starting composition) near the morphotropic phase boundary. The dielectric methods have been complemented for the first time by optical probing. It has been demonstrated that the content of PbTiO₃ in the samples under study is less than that in the starting composition. A suggestion is advanced that, in the samples studied, the stable room-temperature state with no electric field applied is that formed in the mixture of the rhombohedral R and monoclinic M _a phases. It has been found that the number, symmetry, and stability of the phases formed in a field depend on the regime of field application. The E-T phase diagrams have been constructed for different field application regimes. Phase diagrams obtained for the same crystal have been shown to differ for different regimes of field application.     

0.67 PbMg1/3Nb2/3O3-0.33 PbTiO3单晶中软模模式指认

应用显微拉曼技术对弛豫型铁电体0.67PbMg1/3Nb2/3O3-0.33PbTiO3(0.67PMN-0.33PT)的偏振拉曼光谱随温度变化的研究表明,在-196到600°C温度范围内0.67PMN-0.33PT存在两次相变:三方到四方(R-T)相变和四方到立方(T-C)相变。R-T相变的特征是106cm-1软模(-196°C时)随温度的升高而湮没到80cm-1"静态"模式中。依照群论分析,0.67PMN-0.33PT的80cm-1和106cm-1(-196℃时)两个模式分别为E(1TO)和A1(1TO)模。文章对三方相的对称结构(C3v点群)在背向散射配置下不同偏振方向的拉曼散射效率进行了计算。计算结果表明晶体中的A1(1TO)和E(1TO)模式能够通过使用不同的散射配置进行识别。理论计算和实验结果相比较得到了很好的吻合。     

Field cooled and zero field cooled 207Pb NMR and the local structure of relaxor PbMg1/3Nb2/3O3

An isotropic 207Pb NMR spectrum corresponding to the glassy matrix with spherical shell type Pb shifts from the cubic sites, as well as an anisotropic spectral component corresponding to polar nanoclusters with a Pb shift parallel to the [111] direction, have been observed in a PbMg(1/3)Nb(2/3)O3 (PMN) single crystal. This represents a microscopic confirmation of the model of relaxors first proposed by Burns and Dacol. A sudden increase in the intensity of the anisotropic cluster line is seen for electric fields larger than the critical field around 210 K. This demonstrates the occurrence of an orientational percolation type transition to the field-induced ferroelectric phase with about 50% of the Pb nuclei still remaining in the spherical glass matrix. A similar though smaller increase of the intensity of this line is also seen in the zero field cooled data, demonstrating that relaxor PMN is an incipient ferroelectric.     

Transparent ferroelectric ceramics PbMg1/3Nb2/3O3-xPbZr0.53Ti0.47O3: Dielectric and electro-optical properties

Lanthanum-free high-transparency ferroelectric ceramics PbMg_1/3Nb_2/3O₃?xPbZr_0.53Ti_0.47O₃ (PMN-xPZT) have been prepared for the first time by a two-stage sintering method. The dielectric and electro-optical properties of the PMN-xPZT ceramics of different compositions, with the values of x both far from the morphotropic phase boundary (x = 10, 16, 23%) and close to it (x = 33%), have been studied. It has been shown that, in compositions lying closer to the morphotropic phase boundary (x = 23 and 33%), one observes, with no electric field applied, a first-order phase transition to a macrodomain ferroelectric phase, whereas the compositions far from the boundary (x = 10, 16%) persist in the relaxor cubic phase down to the low-temperature domain. It has been found that, in the ceramic with x = 33%, the quadratic electro-optical coefficients have at high temperatures (T > 340 K) the largest value among the relaxor systems, which expands the temperature interval of applicability of these solid solutions in industry.     

Inelastic neutron scattering study of the relaxor ferroelectric PbMg1/3Nb2/3O3 at high temperatures

Results of inelastic neutron scattering experiments between 300 K and 900 K on the relaxor ferroelectric PbMg _1/3 Nb _2/3 O₃ are presented. Within a mode-coupling analysis the data are consistent with the observation of a strongly damped quasi-optic excitation. It is demonstrated that below K a dynamical crossover takes place manifesting itself by a narrow central peak. This crossover is accompanied by the appearance of strong damping of the transverse acoustic phonons, with the damping constant proportional to q⁴. Different physical models of the crossover are discussed. Received 8 February 1999     

A polarized micro-Raman study of a 0.65PbMg1/3Nb2/303-0.35PbTi03 single crystal

Polarized micro-Raman spectra of a 0.65PbMg_1/3Nb_2/3O₃-0.35PbTiO₃ （0.65PMN-0.35PT） single crystal poled in the [001] direction are obtained in a wide frequency range （50-2000 cm 1） at different temperatures.The best fit to the Raman spectrum at 77 K is achieved using 17 Lorenzians to convolute into it,and this is proved to be a reasonable fit.According to the group theory and selection rules of overtone and combinational modes,apart from the seven Raman modes that are from first-order Raman scattering,the remaining ones are attributed to being from second-order Raman scattering.A comparison between the experimental results and theoretical predictions shows that they are in satisfactory agreement with each other.Our results indicate that at 77 K the sample belongs to the rhombohedral symmetry with the C 5 3v （R3m） space group （Z=1）.In our study,on heating,the 0.65PMN-0.35PT single crystal undergoes a rhombohedral → tetragonal → cubic phase transition sequence.The two phase transitions occur at 340 and 440 K,which correspond to the disappearance of the soft mode near 106 cm 1 recorded in VV polarization and the vanishing of the band around 780 cm 1 in VH polarization,respectively.     

Unique features of the crystal structure of the (PbMg1/3Nb2/3O3)0.6-(PbTiO3)0.4 solid solution

An x-ray diffraction study of the paraphase of the (PbMg_1/3Nb_2/3O₃)_0.6-(PbTiO₃)_0.4 solid solution has been found to exhibit a clearly pronounced ferroelectric transition. It is shown that Pb²⁺ ions occupy a special position (000), as opposed to pure PMN and other relaxor ferroelectrics, where they are displaced from it in random directions. The absence of these displacements indicates suppression of frozen-in random electric fields in this compound. Fiz. Tverd. Tela (St. Petersburg) 41, 1282–1285 (July 1999)     

Polarized Raman mapping study of the microheterogeneity in 0.67PbMg1/3 Nb2/3O3‐0.33PbTiO3 single crystal

Polarized micro‐Raman spectroscopy was carried out on the (001) face of a 0.67PbMg_1/3Nb_2/3O₃‐33%PbTiO₃ (PMN‐33%PT) single crystal. The Raman images revealed the spatial variations of the intensity of the Raman bands, suggesting that the structure in the PMN‐33%PT single crystal varied from one micro‐area to another. When changing the polarization direction of the incident light with respect to the selected crystalline axes, the intensities of the Raman modes varied periodically. According to the Raman selection rules (RSRs), the angular dependences of the Raman modes indicated that the PMN‐33%PT single crystal is in the monoclinic phase. Furthermore, the color patterns in the Raman images were associated with the coexistence of the M_A‐ and M_C‐type monoclinic phases in the PMN‐33%PT single crystal. Our results provide useful information for understanding the microheterogeneity of the relaxor PMN‐xPT single crystals with compositions near the morphotropic phase boundary region. Copyright © 2010 John Wiley & Sons, Ltd.     

Bulk spin-wave electrodynamics of an antiferromagnetic plate in a constant external electric field

Using the example of a plate of an easy-axis centrosymmetric antiferromagnet, the conditions are determined under which an external constant electric field qualitatively changes not only the character of refraction of a bulk TM wave incident from vacuum onto the antiferromagnet surface but also the structure of the spectrum of propagating bulk magnons. The relation of the discovered effects to the shape of the refraction surface of TM polaritons is studied.     

E-T phase diagrams of a solid solution of the multicomponent PbZn1/3Nb2/3O3-PbMg1/3Nb2/3O3-PbNi1/3Nb2/3O3-PbTiO3 system near the morphotropic phase boundary

The specific features of the dielectric and pyroelectric responses of a solid solution in the barium-doped multicomponent yPbZn_1/3Nb_2/3O₃-mPbMg_1/3Nb_2/3O₃-nPbNi_1/3Nb_2/3O₃-xPbTiO₃ system of the composition y = 0.0982, m = 0.4541, n = 0.1477, and x = 0.3 near the morphotropic phase boundary have been investigated. It has been assumed that the maxima revealed in the dependences of the reversible permittivity on the electric field strength with both the forward and backward changes in the field (E ₌) are associated with the induced phase transition. Based on the experimental results, the E-T phase diagrams are constructed in the temperature range from ?100 to 150°C for different temperature-field regimes: (i) variation in the electric field E ₌ at a fixed temperature of the sample and (ii) variation in the temperature of the sample at a constant value of E ₌. It has been found that there is a singular point in the E-T phase diagram and that, in the vicinity of this point, the dielectric and pyroelectric responses of the studied ceramics exhibit specific features.     

Piezoresponse imaging and local characterization of ferroelectric domains in Pb(Zn1/3Nb2/3)O3–7%PbTiO3 single crystals

Ferroelectric domain structures of (001)‐oriented Pb(Zn_1/3Nb_2/3)O₃–7%PbTiO₃ (PZN‐7%PT) single crystals were visualized and characterized by piezoresponse force microscopy (PFM). Locally regular domain configurations are found to be possibly related to the stable macroscopic properties in the PZN‐7%PT single crystals. Nanoscale piezoresponse hysteresis loops measured by PFM tip revealed no evidence of local domain switching behavior in the PZN‐7%PT single crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of the electric field on structural transformations and phase boundary for PMg1/3Nb2/3O3-xPbTiO3 single crystals

The influence of different regimes of application of a dc electric field (0 < E < 4 kV/cm) on structural phase transformations and behavior of the phase boundary in [001]-oriented single crystals PMg_1/3Nb_2/3O₃-xPbTiO₃ (PMN-xPT) with compositions near the morphotropic phase boundary (x = 28 and 32%) and far from it (x = 13%) has been investigated. The studies have been performed using optical methods, namely, optical transmittance and small-angle light scattering. It has been revealed that the number, symmetry, and stability of field-induced phases depend on the regime of electric field application. During cooling of the PMN-28PT crystals from the cubic phase in the field (FC regime), the tetragonal phase is induced already in weak fields of ∼0.5 kV/cm, whereas even a field of 3 kV/cm is insufficient for inducing this phase by applying the field in the ferroelectric phase. In the PMN-32PT crystal (which has a composition closer to the morphotropic phase boundary as compared to that of the PMN-28PT crystal) in the FC regime and when the field is applied in the ferroelectric phase, the tetragonal phase is induced already in weak electric fields, even though this phase in the latter case appears to be unstable. The E-T phase diagrams have been constructed for different regimes of field application. The possible factors responsible for the observed differences have been discussed.