Optical investigations of structural phase transformations in PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>-<Emphasis Type="Italic">x</Emphasis>PbTiO<Subscript>3</Subscript> single crystals located at the morphotropic phase boundary

A study has been made of the effect of a dc electric field (0 < E < 4 kV/cm) on the optical transmittance of single-crystal compounds PbMg_1/3Nb_2/3O₃-xPbTiO₃ (PMN-xPT) located at the boundaries of the morphotropic region (x = 32.0 and 36.5%) and directly at the center of the morphotropic region (x = 35%). It is shown that, at temperatures close to the morphotropic phase transition point, the electric field induces two phase transitions in PMN-32PT and PMN-35PT crystals and only one phase transition in PMN-36.5PT. The tetragonal (T) phase induced in all three compounds remains stable after the electric field is removed only in crystals with x = 35.0 and 36.5%, whereas the T phase is metastable and transforms into the monoclinic M _c phase after the field is switched off in the PMN-32PT crystals lying at the boundary of the morphotropic region on the rhombohedral side. It is found that the electric-field-induced intermediate phase M _c in PMN-35PT is inhomogeneous and that M _c transforms into the tetragonal phase in a continuous transition. It is suggested that only the presence of a third orthorhombic phase can account for the continuous character of the transition between the M _c and T phases in PMN-35PT crystals. The results obtained are interpreted in terms of the Devonshire theory for strongly anharmonic crystals. The E-T phase diagrams are constructed for all the crystals.     

Kinetics of nucleation of thermodynamically ordered ferroelectric phases in PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>–<Emphasis Type="Italic">x</Emphasis>PbTiO<Subscript>3</Subscript> crystals with different compositions

The kinetics of electric field-induced nucleation of ordered ferroelectric phases from a mixed glassy relaxor state has been studied in a number of single-crystal (1–x)PbMg_1/3Nb_2/3O₃–xPbTiO₃ (PMN–xPT) solid solutions (x = 29, 33, 35%) lying in a morphotropic phase region. It is shown that the formation of these phases and fast establishment of a macroscopic polarization are preceded by some delay time, depending on the electric field strength and temperature. It is found that the monoclinic phase is thermodynamically stable at room temperature in all the compounds in the time (~3000 s) and electric field (~1 kV/cm) ranges under study, whereas the monoclinic phase of the compound with x = 35% transforms, at temperatures near the temperature of the morphotropic phase transition after insignificant time interval of ~100 s, to another stable ferroelectric tetragonal phase.     

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.     

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.     

Phase transition, structural and electrical properties of Pb(Zn1/3Nb2/3)O3-doped Pb(Ni1/3Nb2/3)O3-PbTiO3 ceramics prepared by solid-state reaction method

Phase pure perovskite (1−x−y)Pb(Ni_1/3Nb_2/3)O₃-xPb(Zn_1/3Nb_2/3)O₃-yPbTiO₃ (PNN-PZN-PT) ferroelectric ceramics were prepared by conventional solid-state reaction method via a B-site oxide mixing route. The PNN-PZN-PT ceramics sintered at the optimized condition of 1185 °C for 2 h exhibit high relative density and rather homogenous microstructure. With the increase of PbTiO₃ (PT) content, crystal structure and electrical properties of the synthesized PNN-PZN-PT ceramics exhibit successive phase transformation. A morphotropic phase boundary (MPB) is supposed to form in (0.9−x)PNN-0.1PZN-xPT at a region of x=32-36 mol% confirmed by X-ray diffraction (XRD) measurement and dielectric measurement. The MPB composition can be pictured as providing a “bridge” connecting rhombohedral ferroelectric (FE) phase and tetragonal one since crystal structure of the MPB composition is similar to both the rhombohedral and tetragonal lattices. Dielectric response of the sintered PNN-PZN-PT ceramics also exhibits successive phase-transition character. 0.64PNN-0.1PZN-0.26PT exhibits broad, diffused and frequency dependent dielectric peaks indicating a character of diffused FE-paraelectric (PE) phase transition of relaxor ferroelectrics and 0.40PNN-0.1PZN-0.50PT exhibits narrow, sharp and frequency independent dielectric peaks indicating a character of first-order FE-PE phase transition of normal ferroelectrics. The FE-PE phase transition of 0.56PNN-0.1PZN-0.34PT is nearly first-order with some diffused character, which also exhibits the largest value of piezoelectric constant d₃₃ of 462pC/N.     

Evolution of the ferroelectric phase in ?001?-oriented (100 ? x )PbMg1/3Nb2/3O3- x PbTiO3 single crystals

The effect of a dc electric field on the nucleation and evolution of the phase with long-range order in a cubic nonpolar matrix in 〈001〉-oriented (100 − x)PbMg_1/3Nb_2/3O₃-xPbTiO₃ single-crystal relaxors as the content of PbTiO₃ is gradually increased (6 ≤ x ≤ 20, where x is the PbTiO₃ content given in molecular percent) is investigated. The optical properties of these solid solutions are studied in different modes of application of an electric field. It is shown that an applied electric field with a strength above a threshold value induces a first-order ferroelectric phase transition with a temperature hysteresis occurring between measurements performed under cooling and heating of the crystal in the electric field. As the PbTiO₃ content or electric field strength increases, the hysteresis becomes less pronounced and the first-order phase transition is suppressed. At x ∼ 20, the induced transition resembles a second-order rather than first-order transformation. It is assumed that, for compositions with x > 10 in electric fields higher than 4 kV/cm, the formation of the rhombohedral phase is accompanied by the appearance of another (possibly, monoclinic) phase associated with the rotation of the polarization vector from the [111] direction of the rhombohedral phase to the [001] direction of the tetragonal phase. Original Russian Text ? L.S. Kamzina, E.V. Snetkova, I.P. Raevskiĭ, A.S. Emel’yanov, Jiayue Xu, Weidong Xiang, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 4, pp. 725–730.     

Electric-field-induced tetragonal phase in [Pb(Mg1/3Nb2/3)O3]0.68–[PbTiO3]0.32 by Raman scattering

ABSTRACT

The paper describes investigation of the electric-field-induced phase transition in PMN-xPT single crystals with x = 0.32 by means of detailed polarized Raman scattering measurements. Field-induced tetragonal state was reached by applying an electric field up to 30 kV/cm along pseudo-cubic direction at a temperature slightly below that of the zero-field rhombohedral–tetragonal phase transition (T_RT). In this field-induced tetragonal state, the angular dependencies of the polarized Raman spectra were recorded and compared with the similar data available for the rhombohedral single-domain and multidomain states.     

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.     

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.     

Effect of the la concentration on the dielectric and optical properties of the transparent ferroelectric ceramics 75PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>-25PbTiO<Subscript>3</Subscript>

The dielectric, optical, and electro-optical properties of transparent ferroelectric ceramics 75PbMg_1/3Nb_2/3O₃-25PbTiO₃ (75PMN-25PT) with different La concentrations (2, 3, and 4 at %) have been studied. It has been shown that all the samples under study undergo a diffuse phase transition, and the degree of diffuseness increases with an increase in the La concentration. The temperature dependences of the optical transmission in different regimes of applying an electric field and the quadratic electro-optical effect have been investigated. It has been found that, at room temperature, the maximum electro-optical effect is observed in the ceramics with a La concentration of 3 at %. This is explained by the fact that the measurement temperature is close to the Vogel-Fulcher temperature at which the minimum electric field is required to induce ferroelectric states from the relaxor phase.     

A comparative Raman study of 0.65(PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>) -0.35(PbTiO<Subscript>3</Subscript>) single crystal and thin film

We report a comparative Raman study of 0.65(PbMg_1/3Nb_2/3O₃)-0.35(PbTiO₃) (PMN-0.35PT) single crystal and thin film. Raman spectra investigation indicates a change in bulk from the high temperature cubic to the tetragonal phase and then to the low temperature Mc monoclinic phase. The transition temperatures are in good agreement with the ones previously observed by dielectric measurements on the same sample. In contrast, we observe no phase transition to the monoclinic phase in the PMN-0.35PT 4000 Å thick film and only a cubic to tetragonal diffuse transition has been determined at high temperature. The enhanced stability of the tetragonal phase and the absence of low temperature monoclinic phase have been attributed to the in plane strain.     

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.     

Dependence of high electric-field-induced strain on the composition and orientation of Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals

Electric-field-induced strain behavior of (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMNT) crystals with different orientations and compositions was investigated for use as electromechanical actuators. Crystallographically, high strains with low hysteresis were achieved for 〈001〉 oriented rhombohedral crystals (29%≤x≤31%) near a morphotropic phase boundary, rather than 〈110〉 and 〈111〉. Domain instability could explain inferior strain levels and large hysteresis for 〈110〉 and 〈111〉 oriented crystals. Ultrahigh strain levels up to 1.8% could be achieved for 〈001〉 oriented PMNT crystals, being related to an E-field induced phase transition. −2 kV/cm negative E-field can be applied to PMNT ferroelectric material with low hysteresis. High strain with low hysteresis makes PMNT crystals promising candidates for high performance solid-state actuators.     

Phase transitions and optical properties in 〈001〉 (1−<Emphasis Type="Italic">x</Emphasis>)PbZn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>−<Emphasis Type="Italic">x</Emphasis>PbTiO<Subscript>3</Subscript> single crystals

The effect of a constant electric field (0 < E < 5 kV/cm) on the optical properties of PbZn_1/3Nb_2/3O₃?xPbTiO₃ (PZN-xPT) crystals with x = 7 and 9% has been analyzed. It has been shown that, at temperatures close to the temperature of the transition from the rhombohedral [R(X)] phase to the tetragonal (T) phase, two induced phase transitions are observed in the electric field, which are associated with the appearance of new intermediate phases M_a and M_c [R(X)-M_a-M_c-T]. Correlation between these two transitions and the PbTiO₃ content x has been found. The E-T phase diagrams have been obtained. The M_c phase in PZN-9PT crystals is found to remain the ground state after the removal of the electric field, whereas the M_c phase in PZN-7PT crystals is metastable and is transformed into the M_a phase after the removal of the electric field.     

Phase coexistence in lead zirconate titanate solid solutions

This paper discusses the phenomena observed in the vicinity of the morphotropic phase boundary in Pb(Ti_1?x Zr_x)O₃ (PZT) solid solutions. The location of the boundary between the stable tetragonal ferroelectric phase and the stable rhombohedral ferroelectric phase is calculated, and an analytical expression for determining the concentration range of the possible coexistence of these phases is derived. According to the numerical estimates, the concentration range can be as much as 20 mol % lead zirconate. However, reliable experimental data in support of these estimates are as yet unavailable.     

Electric field effects on the dielectric and acoustic anomalies of Pb[(Mg1/3Nb2/3)0.83Ti0.17]O3 single crystals studied by dielectric and Brillouin spectroscopies

The effect of the electric field on the dielectric and acoustic properties of Pb[(Mg_1/3Nb_2/3)_0.83Ti_0.17]O₃ single crystals was investigated as functions of temperature and the electric field strength. The dielectric constant and the acoustic mode behaviors exhibited typical relaxor behaviors when there was no bias field. The longitudinal acoustic mode showed splitting under a moderate electric field of 1 kV/cm applied along the [001] direction, indicating coexistence of macroscopic/mesoscopic ferroelectric states and relaxor states. Further increase in the electric field up to 2 kV/cm induced a clear ferroelectric phase transition, which became smeared out due to the proximity of the electric field to the critical point. The electric field-temperature phase diagram of Pb[(Mg_1/3Nb_2/3)_0.83Ti_0.17]O₃ was suggested based on the observed field-induced changes in the dielectric and the acoustic properties.     

Spontaneous phase transition from relaxor to macrodomain ferroelectric state in single-crystal PbSc0.5Nb0.5O3-BaSc0.5Nb0.5O3 solid solutions

The cooling of Pb_1?x Ba_xSc_0.5Nb_0.5O₃ solid solutions with x≤0.04 leads to a spontaneous transition from a relaxor to a macrodomain ferroelectric state, accompanied by anomalous variation of the dielectric and optical properties of the material. As the barium content in the system increases, the relaxor state becomes more stable and eventually “freezes” at x≈0.05. The crystals with x=0.06 exhibited the appearance of a macrodomain ferroelectric phase induced both by an external electric field with a strength of 1.5 kV/cm and by an internal electric field formed in the course of dielectric aging.     

Dependences of the dielectric and pyroelectric properties of (1 ? x)PbFe1/2Nb1/2O3?xPbTiO3 ferroelectric ceramics solid solutions on the PbTiO3 content in a compositional range of 0 ≤ x ≤ 0.08

(1 − x)PbFe_1/2Nb_1/2O_3−x PbTiO₃ (PFN-xPT) ferroelectric ceramics with low dielectric loss and pronounced anomalies of dielectric and pyroelectric properties near the ferroelectric-ferroelectric phase transition was obtained by doping with lithium. The temperature dependence of the position of the morphotropic boundary between the rhombohedral (monoclinic) and tetragonal phases in the x-T phase diagram of the PFN-xPT system was determined for the first time.     

Lattice dynamics and low‐temperature Raman spectroscopy studies of PMN–PT relaxors

In this work we present a Raman scattering study of a specific region of the morphotropic phase boundary (MPB) of the [Pb(Mg_1/3Nb_2/3)O₃]_1−x (PbTiO₃)_x relaxor system. We performed low‐temperature measurement for the x = 0.4 composition in the 20–300 K temperature range, and a detailed analysis of Raman spectra of x = 0.4 and x = 0.37 compositions at 180 K. The analysis of Raman spectra indicates a structural phase transition at around 170 K for x = 0.4. The comparison of Raman data from x = 0.4 and x = 0.37 compositions suggests different phases for these samples at 180 K. These results are in accordance with the tetragonal to monoclinic structural phase transition observed in the PMN–PT MPB and contribute to improve the knowledge of the MPB of this solid solution. Additionally, we have performed the lattice dynamics phonon calculation of the (1 − x) PMN–xPT relaxor in order to best understand its complex Raman spectral properties. The normal mode analyses (at q ∼ 0) were performed by considering tetragonal symmetry for the (1 − x) PMN–xPT system and using the rigid ion model and mean field approximation. Our calculated wavenumber values are in good agreement with experimental and calculated results reported for PbTiO₃ thus providing a reliable assignment of the various Raman modes. The low wavenumber modes are interpreted as arising from a lifting of the degeneracy of the vibrational modes related to Mg, Nb and Ti sites. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparative analysis of the twin and heterophase structures in (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 crystals

The specific features of the coexistence of phases in heavily twinned crystals of the (1?x)Pb(Mg_1/3Nb_2/3)O₃?xPbTiO₃ system in the vicinity of the morphotropic phase boundary (0.30≤x≤0.40) are investigated. The phase transformations in crystals at x = const during cooling are considered at electric field strengths E=0 and 0.1 MV/m. The conditions of the formation of interphase boundaries (zero net strain planes) are determined for different first-order phase transitions. The results of calculating the tetragonal-monoclinic M _C and monoclinic-monoclinic (M _C –M _A ) phase transitions are represented in the form of “twin state-interphase boundary” diagrams. The effect of a 90° domain (twin) structure of the tetragonal phase on the heterophase state associated with the presence of monoclinic phases is analyzed.