LiTaO3 Crystal Research Articles

Design of heterogeneous catalysts with artificially controllable functions using effects of acoustic wave excitation

The effects of surface acoustic waves (SAWs) and resonance oscillation (RO) of bulk acoustic waves on catalytic activity and selectivity were studied in an attempt to design a heterogeneous catalyst which has artificially controllable functions for chemical reactions. The propagation of Rayleigh SAW and shear horizontal leaky SAW through thin Pd catalyst films deposited on poled ferroelectric LiNbO3 and LiTaO3 crystals caused considerable activity increases in ethanol oxidation: the enhancement was much larger for the oxidized than the reduced Pd. Similar effects were observed for a Ni catalyst. The RO effects on catalyst activation for ethanol oxidation were associated with the polarized (positive and negative) surfaces and the vibration modes of the ferroelectric substrates. The thickness extension mode resonance oscillation (TERO) of z-cut LiNbO3 caused different changes in the activation energy and reaction order between the positive and negative plane of the LiNbO3 substrate. Different catalyst activation was induced between TERO and the radial extension mode resonance oscillation (RERO) of a Pb0.95Sr0.05Zr0.53Ti0.47O3 ferroelectric substrate. For ethanol decomposition on a Ag catalyst, the TERO of z-cut LiNbO3 increased ethylene production without significant enhancement of acetaldehyde production, thus demonstrating that TERO has the ability to change the selectivity in the catalytic reaction. Large dynamic lattice displacement, surface potential changes, and work function shifts were observed with TERO. A mechanism of acoustic wave excitation effect on the catalyst activation is discussed.

Birefringence Measurement by Low Coherence Interferometry

We proposed and demonstrated a practical method for simultaneous measurement of the refractive index and the thickness of a transparent plate, based on the low coherence interferometry. This paper suggests that our method is applicable for birefringence measurement using unpolarized light source. Small birefringence of thin medium such as LiTaO3 crystal is measured with high accuracy, by introducing dispersion compensation into the low coherence interferometry.

Leaky modes of channel waveguides with uniaxial anisotropy

An exact numerical method for analyzing the propagation properties of leaky modes of inhomogeneous channel optical waveguides with a complex uniaxial diagonal permittivity tensor is developed. The method is based on solving the system of integro-differential equations formulated with respect to transversal components of the magnetic field and the longitudinal component of the electric field. Some results of investigation of leaky modes of diffused channel waveguides in LiNbO3 and LiTaO3 crystals are given.

Elastic constants of the lithium tantalate crystal in the hypersonic range

Elastic constants of the lithium tantalate LiTaO3 crystal were determined in the hypersonic range by the use of the Brillouin laser light scattering method. Obtained values show variation with respect to ultrasonic measurements. Results are interesting because the same effects are qualitatively different in isomorphic lithium niobate LiNbO3 crystal.

Crystal growth and low coercive field 180° domain switching characteristics of stoichiometric LiTaO3

We grew LiTaO3 single crystals with a composition close to stoichiometry by using a double crucible Czochralski method. The switching field required for 180° ferroelectric domain reversal and the internal fields originating from nonstoichiometric point defects were compared for the stoichiometric and conventional commercially available crystals. The switching fields for the domain reversal in the stoichiometric crystal with a Curie temperature of 685 °C was 1.7 kV/mm. This is about one thirteenth of the switching field required for the conventional LiTaO3 crystals with a Curie temperature near 600 °C. The internal field in the stoichiometric crystal drastically decreased to 0.1 kV/mm.

Studies of the local geometry for Fe3+ in LiTaO3 crystal from EPR data

The EPR zero-field splitting D for Fe3+ in LiTaO3 crystal has been calculated from the microscopic spin-orbit coupling mechanism and the empirical superposition model. It is found that to reach the good fit between the calculated and observed values of D, the Fe3+ ion does not occupy the exact Li+ site, but is required to move about 0.24±0.11 Å in the direction of the -c axis in LiTaO3 crystal. The result is very similar to that for Fe3+ in the isomorphous LiNbO3 crystal obtained from the X-ray standing waves experiment. The reasonableness of the Fe3+ displacement is discussed.

Ferroelectrics as a versatile solid state platform for integrated optics

A high speed electro-optic scanner is demonstrated on a ferroelectric LiTaO3 crystal. The scanner shows a deflection of 39.5 mrad/kV, 13 resolvable spots per kV, and shows no degradation of performance upto 10MHz of driving field. Integration of the scanner with quasi-phase-matched frequency doublers and lenses is discussed.

Investigations of the EPR Zero-Field Splitting and Local Geometry for Mn2+ Ion in LiTaO3 Crystal

The EPR zero-field splitting D for the Mn2+ ion in LiTaO3 crystal has been studied from the microscopic spin-orbit coupling mechanism and the empirical superposition model. From the studies, one can find that to reach a good fit between theory and experiment, the Mn2+ ion does not occupy the exact site of the replaced Li+ ion, but is required to move about 0.022(1) nm in the direction of the c-axis in the LiTaO3 crystal. The result and the reasonableness of the displacement direction are discussed. It appears that both theoretical methods can be used to explain the zero-field splitting of 3d(5) ions in crystals, or, in reverse, to study the local geometry of these ions in crystals from the EPR data.

Investigations of the EPR Zero-Field Splitting and Local Geometry for Mn2+ Ion in LiTaO3 Crystal

Investigations of the EPR Zero-Field Splitting and Local Geometry for Mn2+ Ion in LiTaO3 Crystal

Wall velocities, switching times, and the stabilization mechanism of 180° domains in congruent LiTaO3 crystals

A systematic study of the kinetics of 180° domains as a function of external electric field is presented for Z-cut LiTaO3 single crystal wafers at room temperature using transient current measurements combined with nondestructive and real-time imaging of 180° domains by light microscopy. The switching time, wall velocity, and nucleation rate follow an exponential behavior with the applied field. A model is proposed which shows that the nucleation and sideways growth of domains play approximately equal parts in determining the switching time. A domain stabilization process occurs on the time scale of a few seconds even at electric fields where the switching time is milliseconds or less. We show that this stabilization process has a strong correlation to the internal fields in the crystal.

Catalitically Induced D-D Fusion in Ferroelectrics

A model of deuteron acceleration in ferroelectrical crystals under the process of domain polarization reversal is proposed. Experimental verfication of the model with LiTaO3 crystals saturated with deuterium was fulfilled. It was shown that in the 75 kV/cm a.c. field the neutron emission attributed to D-D fusion is two order magnitude higher the Jones level.

Near-field scanning optical microscopy of ferroelectric domain walls

We have observed domain walls in ferroelectric LiTaO3 crystals using a polarization and phase sensitive near-field scanning optical microscope. The strain induced birefringence was used to observe the domain walls. The domain walls are measured to be 1 μm wide and show a variation of strain along the domain walls probably due to defects. These measurements allow an estimate of the birefringence at the domain wall of 6×10−5 and associated shear strain of 4×10−5.

Elastic properties of single- and multi-domain crystals of LiTaO3

A basic study of the differences in elastic properties between single- and multi-domain crystals of LiTaO3 is conducted by measuring the longitudinal velocities for X-, Y-, and Z-cut specimens and the shear velocities for Z-cut specimens. Two sets of X-, Y-, and Z-cut specimens are prepared: one is for normal (single-domain) specimens and the other is for perfectly depoled (multi-domain) specimens. For the longitudinal wave propagation directions along the Y and Z axes, the velocities for the single-domain specimens, due to piezoelectricity, are 91.5 m/s (1.59%) and 92.7 m/s (1.50%) larger than those for the multi-domain specimens, respectively. On the other hand, for the X-axis longitudinal and Z-axis shear wave propagation directions, piezoelectricity is uncoupled, but the very interesting velocity changes are that the longitudinal and shear velocities for the single-domain specimens are 48.4 m/s (0.87%) and 135.6 m/s (3.79%) smaller than those for the multi-domain specimens, respectively. These differences are introduced by the poling operation for multi-domain LiTaO3 crystals. Four elastic constants of c11, c33, c44, and c14 in the multi-domain state are determined.

Line-focus acoustic microscopy measurements of acoustic properties of LiTaO3 crystal plates with an inversion layer

Inversion layers of 2 μm and 30 μm thickness were formed at the negative dipole-end (−c) face of a Z-cut LiTaO3 crystal plate by proton exchange followed by heat treatment. The phase velocities of leaky surface acoustic waves (LSAWs) on both the positive (+c) and negative (−c) faces of the plate were measured by line-focus acoustic microscopy versus the angle of propagation, at a frequency of 225 MHz, and the results were compared with theoretical predictions. It is shown that for an inversion layer of 30 μm thickness the phase velocities of LSAWs on the +c and −c faces are the same, and almost equal to the velocities of the virgin plate. This suggests that the material constants, which are decreased due to the proton exchange, are restored to the original values by the heat treatment.

Waveguide properties of regular domain structure in LiTaO3 crystal

This paper reports a scanning electron microscopy study of the surface acoustic wave interaction with regular domain structure in LiTaO3 crystal. The regular domain structure was formed by thermoelectrical treatment after growth. The process of the surface acoustic wave propagation along domain structure and waveguide properties of the domain structure were investigated.

Temperature-Dependent Raman Study on Vibrational Modes in LiTaO3

In this paper the results of temperature-dependent Raman study on the vibrational modes in LiTaO3 crystals are presented. It is found that the two low-frequency A1 modes show significant changes during the temperature changing process. “Modes softening” and “frequency-repulsion” effect was observed and dicussed.

Photoluminescence of LiTaO3:Pr

Single crystals of LiTaO3 doped with praseodymium were grown by the Czochralski method from congruent melt and their optical properties were examined. It has been found that the Pr3+ ions in LiTaO3 occupy several nonequivalent sites differing in the crystal field strength. In addition, the structural disorder associated with Li deficiency gives rise to strong inhomogeneous broadening of both the optical absorption and emission lines. In contrast to isostructural LiNbO3:Pr, the relaxation of the excited P03 level of praseodymium is governed by radiative transitions, which terminate on excited multiplets and make the LiTaO3:Pr3+ crystals promising for four-level lasing in the visible range.

High-frequency resonance in acoustic superlattice of periodically poledLiTaO3

An electric poling method has been used to prepare microstructured LiTaO3 crystals with periodically inverted-ferroelectric domains. By using these crystals as acoustic superlattices, both an “in-line” scheme and a “cross-field” scheme for acoustic excitation have been realized. The experimental results are in good agreement with the theoretical analysis. It is expected that these results may be applied to a bulk-acoustic device operating at a frequency high above 450 MHz.

Integrated intracavity quasi-phase-matched second harmonic generation based on periodically poled Nd:LiTaO3

Integrated intracavity quasi-phase-matched second harmonic generation (QPM-SHG) has been demonstrated in a periodically domain inverted Nd:LiTaO3 crystal which functions simultaneously as a gain and nonlinear medium. Lasing at 1.082 μm and simultaneous QPM-SHG at 541 nm has been established by pumping near 806 nm. The effect of doping on the domain reversal voltage of LiTaO3 and the photorefractive effect have also been investigated. It is found that optical damage can be avoided by heating above 80 °C.

Radiation Damage Effects in Ferroelectric Litao3 Single Crystals

ABSTRACTZ-cut lithium tantalate (LiTaO3) ferroelectric single crystals were irradiated with 200 keV Art++ ions. LiTaO3 possesses a structure that is a derivative of the corundum (A12O3) crystal structure. A systematic study of the radiation damage accumulation rate as a function of ion dose was performed using ion-beam channeling experiments. An ion fluence of 2.5•1018 Ar2+ ions/m2 was sufficient to amorphize the irradiated volume of a LiTaO3 crystal at an irradiation temperature of ∼120K. This represents a rather exceptional susceptibility to ion-induced amorphization, which may be related to a highly disparate rate of knock-on of constituent lattice ions, due to the large mass difference between the Li and Ta cations. We also observed that the c− end of the ferroelectric polarization exhibits slightly higher ion dechanneling along with an apparent greater susceptibility to radiation damage, as compared to the c+ end of the polarization.