L. S. Kamzina

Origin of the giant electro-optic Kerr effect in La-doped 75PMN-25PT transparent ceramics

Transparent ceramics of La-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) x/75/25 are prepared, and the ferroelectric domains, dielectric, and ferroelectric properties of x/75/25 are investigated. A double hysteresis loop and small fingerprint domains with uniform distribution observed for 3/75/25 indicate an intermediate ferroelectric state. The dielectric behavior under dc bias and the evolution of the hysteresis loop with increasing electric field for 3/75/25 indicate an electric field-induced phase transition, and it is proposed that the unstable intermediate ferroelectric state which would experience obvious field-induced phase transition is the origin of the giant electro-optic Kerr effect observed in La-doped PMN-PT 3/75/25.

Electro-optical properties of PMN-xPT compounds: Single crystals and transparent ferroelectric ceramic

The electro-optical properties of the PMN-xPT single-crystal relaxor solid solutions with different PT contents (x = 6, 10, 13%) and the PLMN-25PT transparent ceramic with a La content of 3%, which has been synthesized for the first time, have been studied at room temperature. It has been shown that the dependence of the quadratic electro-optical coefficients on the PT concentration in single crystals passes through a maximum at x ∼ 13%. It has been revealed that, although the PT concentration in the PLMN-25PT ceramic is above 13%, this material exhibits the largest quadratic electro-optical coefficients and the lowest half-wave voltage among all the known relaxor systems. Possible origins of the above phenomena have been discussed.

Kinetics of the phase transition in crystals PbIn1/2Nb1/2O3–PbMg1/3Nb2/3O3–xPbTiO3

The time dependences of the optical transmission, velocity of sound, and elastic constants at room temperature in a number of the [001]-oriented PbIn1/2Nb1/2O3–PbMg1/3Nb2/3O3–xPbTiO3 single crystals with the compositions lying both far from the morphotropic phase boundary and in its vicinity have been investigated. The analysis of the data obtained has been carried out. It has been shown that, in all the studied crystals, phase transitions induced by an electric field occur in two stages: the first stage is an incubation period associated with a small increase in the polarization of a part of the sample being in the glass phase, and the second phase (after the incubation period τ) is a rapid increase in the polarization and the formation of a long-range order. It has been found that the time τ depends on how close is the temperature of measurements to the Vogel–Fulcher temperature Tf. The closer is the temperature of measurements to the Vogel–Fulcher temperature Tf, the weaker is the electric field required to be applied to the sample in order to induce a ferroelectric phase. It has been demonstrated that the phase state of the studied crystals is unstable, which manifests itself in a strong dependence of the incubation period τ on the time between the annealing of the sample and the beginning of the measurements. The stability of the phase state depends on the PbTiO3 concentration: an increase in the concentration leads to a significant increase in the stability.

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(In1/2Nb1/2)O3-35PbMg1/3Nb2/3O3-32PbTiO3 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.

Dielectric and optical properties of Pb(Mg1/3Nb2/3)0.8Ti0.2O3 (PMNT-0.2) ferroelectric relaxor single crystals

The dielectric and optical (optical transmission, small-angle light scattering, birefringence) properties of PMNT-0.2 single crystals and their variation induced by a dc electric field have been studied. The birefringence was found to increase anomalously at the transition from the rhombohedral ferroelectric to the inhomogeneous relaxor phase (the spontaneous ferroelectric transition temperature Tsp). Below Tsp, the dielectric and optical properties were observed to exhibit anomalies originating from reorientation and growth of domains in size. Unlike ferroelectric relaxors of the type of PbB′1/3B′2/3O3 and PbB′1/2B′1/2O3, in PMNT-0.2 neither induction of the ferroelectric phase by an electric field nor thermally stimulated destruction of the ferroelectric state occurs through the percolation mechanism (i.e., they are not accompanied by anomalously narrow maxima in small-angle light scattering). This is attributed to the inhomogeneous structure of the relaxor phase, as a result of which the phase transition does not take place simultaneously in various regions of the crystal.

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

Lanthanum-free high-transparency ferroelectric ceramics PbMg1/3Nb2/3O3−xPbZr0.53Ti0.47O3 (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.

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 PMg1/3Nb2/3O3-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.

Evolution of the ferroelectric phase in 〈001〉-oriented (100 − x)PbMg1/3Nb2/3O3-xPbTiO3 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)PbMg1/3Nb2/3O3-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.

Electric-field-induced phase transitions in -oriented PZN-9PT and PMN-35PT single crystals

Effects of a constant electric field (0 < E < 5 kV/cm) on the optical transmission of 91PbZn1/3Nb2/3O3-9PbTiO3 (PZN-9PT) and 65PbMg1/3Nb2/3O3-35PbTiO3 (PMN-35PT) single crystals belonging to the morphotropic regions of these solid solution systems have been studied. At temperatures close that of the morphotropic phase transition, the applied electric field induces two new intermediate monoclinic phases (Ma and Mc) in PZN-9PT and a single intermediate monoclinic phase in PMN-35PT crystals. In PMN-35PT, the new phase is inhomogeneous; in PZN-9PT, the transition from Ma to Mc has a continuous character. The E-T phase diagrams for both crystals are constructed. The results are interpreted within the framework of the Devonshire theory of strongly anharmonic crystals.

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 30PbIn1/2Nb1/2O3-37PbMg1/3Nb2/3O3-33PbTiO3 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.