xNbxO3 Crystals Research Articles

Enhanced electro-optic modulation stability in KTa1−xNbxO3 crystal by direct current electric field

Enhanced electro-optic modulation stability in KTa1−xNbxO3 crystal by direct current electric field

Strong pyroelectric enhancement induced by the evolution of PNRs in paraelectric-phase KTN crystals

KTa1−xNbxO3 crystals exhibit excellent piezoelectric, ferroelectric, and electro-optical properties near the phase transition point, owing to the evolution of polar nanoregions (PNRs). This paper discusses the physical properties of the PNRs in three characteristic temperature ranges and analyzes the dielectric relaxation properties of the crystals. The effects of different heating rates and initial temperatures on the pyroelectric effect are discussed, and the influence of small electric fields on increasing the pyroelectric coefficient is investigated. The polarization characteristics of the crystal were obtained according to the change in the pyroelectric performance, and the influence of different conditions on the dynamic response of the PNRs was analyzed. It is proposed that the evolution of PNRs, induced by external coupling with an internal electric field, significantly affects macroscopic performance.

Surface modification of LiNbO3 and KTa1−xNbxO3 crystals irradiated by intense pulsed ion beam

In this work, we studied the surface modification of LiNbO3 and KTa1−xNbxO3 irradiated by intense pulsed ion beam, which was mainly composed of H+ (70%) and Cn+ (30%) at an acceleration voltage of about 450kV. The surface morphologies, microstructural evolution and elemental analysis of the sample surfaces after IPIB irradiation have been analyzed by scanning electron microscope, atomic force microscope, X-ray diffraction and energy dispersive spectrometer techniques, respectively. The results show that the surface morphologies have significant difference impacted by the irradiation effect. Regular gully damages range from 200 to 400nm in depth appeared in LiNbO3 under 2J/cm2 energy density for 1 pulse, block cracking appeared in KTa1−xNbxO3 at the same condition. Surface of the crystals have melted and were darkened with the increasing number up to 5 pulses. Crystal lattice arrangement is believed to be the dominant reason for the different experimental results irradiated by intense pulsed ion beam.

Anomalous laser deflection phenomenon based on the interaction of electro-optic and graded refractivity effects in Cu-doped KTa1−xNbxO3 crystal

An abnormal laser deflection phenomenon in a copper-doped KTa1−xNbxO3 (Cu:KTN) crystal is demonstrated in this Letter. A near-50 mrad beam deflection angle was observed when a voltage of 1.2 kV was applied to a Cu:KTN block with size of 2.8 mm × 1.2 mm × 7.5 mm at room temperature. The special features of this deflection phenomenon are that the laser beam deflection direction is perpendicular to the electric field direction, and the beam deflection angle remains unchanged when the electric field direction is reversed. The operating principle of the phenomenon is investigated and the origin of the deflection phenomenon is attributed to an interaction between the graded refractivity effect and the quadratic electro-optic effect of the crystal.

Changes in permittivity of KTa1−xNbxO3 crystals induced by electron injection in relation to nonlinear dielectric response

We observed large increases in the capacitance of a KTa1−xNbxO3 (KTN) optical beam deflector that were induced by electron injection. The increases were not caused by changes in the electrode interface but rather by changes in the permittivity of the bulk crystal. In the paraelectric phase, the KTN crystal exhibited a nonlinear dielectric response with double hysteresis loops in the D–E curves. We ascribed the permittivity change to this nonlinear phenomenon.

Impact of polar nanoregions on the quadratic electro-optic effect in K0.95Na0.05Ta1−xNbxO3 crystals near the Curie temperature

The quadratic electro-optic effect in K0.95Na0.05Ta1−xNbxO3 crystals near the Curie temperature was investigated. Both the electro-optic coefficients |R11| and |R12| decreased rapidly as the temperature increased beyond the Curie point. Interestingly, the ratio |R11/R12| increased. The polar nanoregions found in K0.95Na0.05Ta1−xNbxO3 crystals near the Curie temperature are believed to be responsible for this effect. A phenomenological model is proposed to analyze the impact of these polar nanoregions on the quadratic electro-optic effect.

Space-charge-controlled electro-optic effect: Optical beam deflection by electro-optic effect and space-charge-controlled electrical conduction

This paper describes the experimental and theoretical studies of an anomalous optical beam deflection phenomenon based on electrooptic effect and space-charge-controlled electrical conduction. In the experiment, a large deflection angle of 250mrad (=14.3°) has been observed by applying ±250V to a 0.5-mm-thick KTa1−xNbxO3 crystal with a short interaction length of 5.0mm. The crystal has a rectangular shape with uniform electrodes and there is no prism shape involved which is a common geometrical shape of crystal, electrode, or ferroelectric domain in the conventional electro-optic deflectors. The operating principle is investigated and it is found that the space-charge-controlled electrical conduction in the crystal plays an essential role in this deflection phenomenon. The electrical conduction is carried by electrons injected from the Ohmic contact of the electrode with the crystal. The injected electrons induce the space-charge effect and the electric field becomes nonuniform between the electrodes. The theoretical analysis shows that the electric field has a square-root dependence on the distance from the cathode. As a result, a linearly graded refractive index is induced by the electrooptic Kerr effect of the crystal and the optical beam is cumulatively deflected as it propagates in the crystal. We named this effect the “space-charge-controlled electro-optic effect” and the factors related to the onset of this effect are also discussed.

Wide-angle, low-voltage electro-optic beam deflection based on space-charge-controlled mode of electrical conduction in KTa1−xNbxO3

An electro-optic beam deflector with unprecedented performance is demonstrated. A full deflection angle of 250mrad (=14.3°) has been achieved by applying only ±250V to a 0.5-mm-thick KTa1−xNbxO3 crystal with a short interaction length of 5.0mm. The operating principle is investigated and the origin of the deflection phenomenon is attributed to a nonuniform electric field induced by space-charge-controlled electrical conduction in the crystal.

Phase transition in dilute KTN crystal investigated by Raman scattering measurements

The light depolarization and the Raman scattering spectrum were measured in a KTa1−xNbxO3 crystal with a dilute Nb concentration (1.2%). Measurements were performed on cooling to 10 K without and then with an electric field. The unexpected Raman lines detected well above TC are attributed to one-phonon density of states. The dependence of these lines as functions of temperature and electric field reveals the formation of polar clusters which grow in the paraelectric phase on cooling and some peculiarities in the mechanism of the phase transition. Copyright © 2005 John Wiley & Sons, Ltd.

Light-Induced charge transport in tetragonal KTa1−xNbxO3:Fe crystals

Abstract The light-induced charge transport in tetragonal KTa1−xNbxO3 crystals with different Fe concentrations is investigated. The experimental results of holographic measurements for intensities up to 1 kW/m2 can be well described by a model which assumes one kind of photorefractive centers with both, electron-hole competition and space charge field limitations due to the available trap density. The results at high intensities lead to the assumption of additional shallow traps.

Ferroelectric domain structures and phase transitions in KTa1−xNbxO3 crystals

Domain configurations and structures of ferroelectric KTa1−x NbxO3 crystals in both orthorhombic and tetragonal phases are studied by a polarizing microscope. It is found that the domain patterns vary in plates of different thicknesses. The domain evolution and new phase nucleation during the first-order orthorhombic-tetragonal-cubic phase transitions with large thermal hysteresis are directly observed under polarized light. The emergence of a large number of microdomains upon cooling is revealed and discussed.

Studies of photorefractive diffraction dynamic in paraelectric KTa1−xNbxO3 crystals

The dynamics of photorefractive diffraction in paraelectric KTa1−xNbxO3 crystals during writing, reading, and erasing have been studied systematically. Experimental observations related not only to the diffraction from the first-order photorefractive grating but also to that from the second-order photorefractive grating, and where a writing beam with spots smaller than, as well as larger than, the entrance surface of the crystal was used. All the complicated behaviors observed have been explained qualitatively. An electron-hole transport model and a nonequilibrium screening model have been applied, and the existence of an internal dc electric field induced during writing simultaneously by an optical field and an externally applied field has been suggested and demonstrated. The significant influence of this induced field is indicated.

The charge state of Mn and defect dynamics in manganese doped KTaxNb1−xO3

The EPR spectra of Mn impurities in KTa1−xNbxO3 crystals (X≂0.03) is studied in the 110–560 K temperature range. Intensity measurements do not support a change in the Mn charge state in the 100–140 K temperature range. The room temperature g factor and hyperfine constant values, g=2.000±0.001 and A=(84.9±0.02)×10−4 cm−1 are very similar to those of Mn2+ in KTaO3 at low temperatures. Thermally induced low-temperature change in the Mn charge state is therefore unlikely. The motional narrowing phenomenon observed at high temperatures (300 K<T<600 K) is very probably due to fast hopping of Mn2+ ions (which sit off-center on K+ sites) between three magnetic inequivalent sites. This is strongly supported by a relaxation matrix analysis of the narrowing which shows that the hopping rate can be characterized by an Arrhenius equation with a low activation energy E=(0.065±0.01) eV which is very similar to the corresponding value in Li:KTaO3, and a preexponent factor 1/τ0=4.5×1012 s−1.