Nb2O6 Crystals Research Articles

Microscopic Raman spectroscopy in the vicinity of domain wall of (Na,K)NbO3 piezoelectrics

The domain walls of Mn-doped (Na,K)NbO3 (NKN) crystals and ceramics have been measured by spectroscopy methods. Microscopy-Raman and infrared (IR) spectroscopies were performed vertically to lamellar domain structures by line mapping. Regarding the crystals, large changes were confirmed in the vicinity of domain walls. Both the Raman shift and the peak intensity at approximately 600 cm−1, which include the symmetric stretching modes of the oxygen octahedron, were observed. Similar changes were also characterized for electrically polarized NKN ceramics. In addition, the permittivity of NKN crystals increased in the vicinity of the domain wall, which was measured by IR spectroscopy. These results were attributed to the changes in the oxygen octahedron structures due to local changes in spontaneous polarization directions in the vicinity of the domain walls.

Near-infrared waveguide formation and RBS/channeling spectrometry analysis for damage in calcium barium niobate crystals via ion implantation

We report on the fabrication of planar waveguide structures in calcium barium niobate crystals via C ion implantation at room temperature. The SRIM code was applied to calculate damage profiles of the C ions implanted into Ca0.32Ba0.68Nb2O6 crystals. The low-damage profiles in the near-surface of the implanted regions were verified by Rutherford backscattering/channeling spectrometry. The waveguide characteristics were investigated in the near-infrared bands. The propagation loss of the waveguide was estimated to be 0.88 dB/cm.

X-ray powder diffraction methods for the determination of composition and structural parameters of Cr- and Ni-doped Sr0.61Ba0.39Nb2O6 crystals

The possibility of using the Rietveld method for refinement of main structural parameters of both nominally pure (SBN-1) and Cr- (SBN-2: Cr2O3, 0.01wt.%) and Ni- doped (SBN-3 and SBN-4: Ni2O3, 0.05wt.% and 1.0wt.%, respectively) ground relaxor-ferroelectric crystals of initial composition Sr0.61Ba0.39Nb2O6, grown by the modified Stepanov technique, has been shown. It was established that the general composition of the crystals can be described as Sr∼0.55Ba∼0.39Nb2O6−δ with possible vacancies in the oxygen sites; the composition of SBN-4 crystal differs from other samples by another distribution of Sr ions over the crystallographic sites of the structure. The correlation between the thermal parameters of oxygen atoms and the disorder on their sites as well as the Ni content in SBN-3 and SBN-4 crystals has been found. The relationship between the unit cell parameters of undoped and Cr- and Ni-doped Sr0.61Ba0.39Nb2O6 crystals and Sr and Ba content, and second-order nonlinear susceptibility values, χ(2), has been revealed.

Ferroelectric domain structures in <001>-oriented K0.15Na0.85NbO3 lead-free single crystal

In this work, ferroelectric domain structures of <001 >-oriented K0.15Na0.85NbO3 single crystal are characterized. Transmission electron microscopy (TEM) observation revealed high-density of laminate domain structures in the crystal and the lattices of the neighboring domains are found to be twisted in a small angle. Superlattice diffraction spots of 12{eeo} and 12{ooe} in electron diffraction patterns are observed in the crystal, revealing the a+a+c− tilting of oxygen octahedral in the perovskite structure. The piezoresponse of domains and in-situ poling responses of K0.15Na0.85NbO3 crystal are observed by piezoresponse force microscopy (PFM), and the results assure its good ferroelectric properties.

Domain size engineering in 0.5%MnO2-(K0.5Na0.5)NbO3 lead free piezoelectric crystals

The piezoelectric property of [001]-oriented 0.5%MnO2-(K0.5Na0.5)NbO3 (Mn-KNN) crystals was studied as a function of domain size, being poled with different electric fields at 205 °C (above orthorhombic to tetragonal phase transition temperature To-t). The piezoelectric coefficients d33 and relative dielectric constants εr were found to increase from 270 pC/N to 350 pC/N and 730 to 850 with the domain size decreasing from 9 to 2 μm, respectively. The thermal stability of piezoelectric property was investigated, where the d33 value for [001]-oriented Mn-KNN crystals with domain size of 2 μm was found to decrease to 330 pC/N at depoling temperature of 150 °C, with minimal variation of ∼6%. The results reveal that domain size engineering is an effective way to improve the piezoelectric properties of Mn-KNN crystals.

Estimation of electrooptic coefficients of LiNbO3 and Sr x Ba(1 − x)Nb2O6 crystals by modulation of light reflection coefficient

A method of estimating the electrooptic coefficients of crystals by the magnitude of modulation of the reflection coefficient of ordinarily and extraordinarily polarized light incident on the surface of an electrooptic medium is considered. The induced birefringence in an alternating electric field is measured for the LiNbO3 and SrxBa(1 − x)Nb2O6 (x = 0.61) crystals. From the measured data, the r13, r33, and r22 electrooptic coefficients are calculated.

Blockage of domain growth by nanoscale heterogeneities in a relaxor ferroelectric Sr0.61Ba0.39Nb2O6

The growth of localized subsurface domains in a relaxor ferroelectric Sr0.61Ba0.39Nb2O6 is studied using the technique of piezoresponse force microscopy (PFM). Ferroelectric domains are created by applying moderate voltages of 10–50 V to the conductive tip of a scanning force microscope brought into contact with a nonpolar face of a Sr0.61Ba0.39Nb2O6 crystal. PFM images of written domains are acquired and analyzed quantitatively to determine the domain length along the polar axis and its width in the transverse direction. The dependences of domain sizes on the applied voltage, pulse duration, and the time passed after completion of the voltage pulse are reported and analyzed theoretically. It is shown that the observed kinetics of domain growth can be explained by the creep of domain boundaries occurring in the presence of random electric fields inherent in Sr0.61Ba0.39Nb2O6. The comparison of measured domain sizes with their equilibrium values calculated with the aid of the thermodynamic theory demonstrates that the growth of subsurface domains in Sr0.61Ba0.39Nb2O6 is blocked by nanoscale heterogeneities characteristic of this relaxor ferroelectric. These results may have important implications for the development of nonlinear optical devices based on nanoheterogeneous ferroelectrics.

Optical waveguide properties of Ca0.4Ba0.6Nb2O6 crystal formed by oxygen ion irradiation

We report the fabrication of a planar optical waveguide in a Ca0.4Ba0.6Nb2O6 crystal by irradiation with 6.0MeV oxygen ions. We measured the guiding mode by the prism-coupling method at 633nm and 1539nm. The near-field intensity distributions were measured by the end-face coupling setup at a wavelength of 633nm. The reflectivity calculation method (RCM) was used for reconstructing refractive index profiles. SRIM was used to simulate the electronic and nuclear stopping power caused by oxygen ion irradiation, and the finite-difference beam propagation method (FD-BPM) was used to simulate the near-field intensity distributions. Micro-Raman spectra were measured at room temperature in air to study the differences between the substrate and waveguide region.

Complete set of material constants of single domain (K, Na)(Nb, Ta)O3 single crystal and their orientation dependence.

A self-consistent complete set of dielectric, piezoelectric, and elastic constants for single domain Ta modified (K, Na)NbO3 (KNN) crystal was determined. This full set constant for single domain KNN-based crystals allowed the prediction of orientation dependence of the longitudinal dielectric, piezoelectric, elastic coefficients, and electromechanical coupling factors. The maximum piezoelectric and electromechanical properties were found to exist near [001] C . In addition, material constants of [001] C poled domain engineered single crystal with 4 mm symmetry were experimentally measured and compared with the calculated values. Based on this, extrinsic contribution to the piezoelectricity was estimated to be ∼20%.

Investigation of Carbon ion-implanted waveguides in tungsten bronze (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 single crystal

Planar optical waveguides were fabricated in (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 (CSBN25) crystal by 6.0-MeV C+ ion implantation with fluences of 2, 4 and 6×1014ions/cm2 at room temperature. The mode parameters, refractive indices profiles are measured and the refractive indices behavior in the waveguide region is discussed. The shape of nuclear energy loss distribution of the C+ implantation was similar to those of the waveguide refractive index profiles, which means an inherent relationship between the waveguide formation and the energetic energy deposition. The extraordinary refractive index has a small positive change in the surface region after the implantation.

Tetragonal-to-Tetragonal Phase Transition in Lead-Free (KxNa1−x)NbO3 (x = 0.11 and 0.17) Crystals

Lead free piezoelectric crystals of (KxNa1−x)NbO3 (x = 0.11 and 0.17) have been grown by the modified Bridgman method. The structure and chemical composition of the obtained crystals were determined by X-ray diffraction (XRD) and electron probe microanalysis (EPMA). The domain structure evolution with increasing temperature for (KxNa1−x)NbO3 (x = 0.11 and 0.17) crystals was observed using polarized light microscopy (PLM), where distinguished changes of the domain structures were found to occur at 400 °C and 412 °C respectively, corresponding to the tetragonal to tetragonal phase transition temperatures. Dielectric measurements performed on (K0.11Na0.89)NbO3 crystals exhibited tetragonal to tetragonal and tetragonal to cubic phase transitions temperatures at 405 °C and 496 °C, respectively.

Waveguide and Raman spectroscopic visualization in C-implanted Ca_020Ba_080Nb_2O_6 crystal

Ca0.20Ba0.80Nb2O6 (CBN-20) crystal has been implanted by 5MeV carbon ions with the fluence of 1 × 1015 ions/cm2. Based on the prism coupling and end face coupling measurements, the light could propagate along with ordinary light direction in the implanted sample which convinced that planar optical waveguide was formed successfully on CBN-20 crystal after C-ion implantation process. The peak position and intensity of Raman spectra have shown obvious changes between the waveguide layer and the substrate, therefore the Raman spectra can be used to visualize the damage or defects produced during the implantation process in the CBN-20 crystal.

Structural peculiarities and point defects of undoped and Cr- and Ni-doped Sr0.61Ba0.39Nb2O6 crystals

Crystals of strontium barium niobate solid solutions, both nominally pure Sr0.61Ba0.39Nb2O6 and doped with transition metal (Cr3+ and Ni3+) ions, have been investigated by X-ray diffraction. The chemical composition of the undoped crystal was determined taking into consideration vacancies in niobium Nb(2) and oxygen sites and the statistical distribution of strontium in two (Sr(1) and Sr(2)) sites in the tetragonal tungsten bronze type crystal structure. It was established that the introduction of chromium or nickel oxides into the melt initial composition greatly influences the strontium and barium content in the crystals obtained and the distribution of these species in the crystallographic structure. The probability of finding the transition metal ions in regular and interstitial positions depending on their concentration and valence state is discussed.

Crystallographic Orientation of (Li,Na,K)NbO<sub>3</sub> Lead-Free Piezoelectric Crystal

Li,Na,K)NbO3 (LNKN) crystals were grown by an infrared convergence-type floating zone (FZ) method using SrTiO3 seed crystals to control the crystallographic orientation. The crystals were grown along the [10 direction of SrTiO3 seed crystal. It was a critical condition for the crystal growth that the descending speed of an upper shaft in the FZ furnace was faster than that of the lower shaft. The grown crystal sizes were about 10 mm in length and 5 mm in diameter. A relation between the Li content and Tc was investigated, and the result was compared with the case of polycrystalline ceramic samples.

Creation of domains and domain patterns on the nonpolar surface of Sr x Ba1 − x Nb2O6 crystals by atomic force microscopy

Microdomains and microdomain patterns have been recorded by applying dc voltages to the probe of an atomic force microscope contacting the nonpolar surface in a barium-strontium niobate ferroelectric crystal. Processes of the formation of microdomains have been investigated. It has been shown that the frontal growth of domains on the nonpolar surface is described by a viscous-friction-type law. The features of the formation of stable domains associated with the back-switching effects have been revealed. Oppositely oriented domains (“head-to-head” and “tail-to-tail”) have been obtained in polydomain crystals. Domain gratings with the reciprocal vector G = 2Π/Λ (where Λ = 3.6 and 8 μm is the grating period), which is parallel and perpendicular to the polar Z axis, have been written by the vector lithography method. Gratings with G ‖ Z, which form a system of 180° linear domains of opposite signs (head to head and tail to tail), hold for no less than several days.

Materials Characterization of Potassium Sodium Niobate based Tellurite Glass-Ceramics

In this research, materials characterization of transparent glass-ceramics containing ferroelectric potassium sodium niobate (K0.5Na0.5)NbO3 (KNN) crystals in a tellurite glass system were studied. The samples were prepared via an incorporation method. Glass-ceramics containing KNN crystals were successfully fabricated by mixing KNN calcined powder with TeO2 of about 70 and 80 mol% and melting at 800°C for 15 min in a platinum crucible. The prepared glasses were then subjected to heat treatment at 350–550°C. The optical properties of the samples were characterized by UV-Vis-NIR and ellipsometer. It was found that heat treatment temperature had significantly affected the optical properties. XRD patterns of the glass-ceramics revealed an amorphous-like structure with different degrees of crystallinity. SEM results confirmed the XRD data, where the degree of crystallinity increased with increasing heat treatment temperature.

Electronic and Optical Properties of Strontium Barium Niobate Single Crystals

Electronic structure of Sr x Ba1- x Nb2O6 crystals in the energy range involving the valence and conduction bands has been studied theoretically and experimentally using the DFT-based ab initio VASP code and the spectroscopic ellipsometry method with synchrotron radiation. The Sr0.61Ba0.39Nb2O6 sample of the congruently melting composition is characterized by the greatest difference of the experimental dielectric function ϵ(E) compared to the non congruently melting compositions of Sr x Ba1- x Nb2O6 (x = 0.40, 0.55, 0.65, 0.75). Electronic band structures of Sr0.60Ba0.40Nb2O6 and LiNbO3 crystals in the energy range of 6–8 eV and the corresponding dielectric functions ϵ(E) in the photon energy range of 3–10 eV have been found to be similar, what is caused by similar octahedral NbO6 complexes in the crystals.

Electro-Optic Tuneable of Direct Current Voltage in Ring Resonator

In this paper, a new design of the electro-optical tuning voltage in buried fiber ring resonator (BFRR) system is proposed. The crystals of LiNbO3, (Ba, Sr)TiO3, K(Ta, Nb)O3 and KH2PO4 are used as electro-optic core materials. The applied voltage can generate different refractive index deformation when used different electro-optic crystals. Different electro-optic crystals produce distinct maximum power loss within BFRR. The power loss in an electro-optic crystal can be controlled by tuning the applied voltage. The K(Ta, Nb)O3 crystal produce maximum power loss with lower voltage compared to other crystals.

Dielectric maximum temperature non-monotonic behavior in unaxial Sr0.75Ba0.25Nb2O6 relaxor seen via acoustic emission

[100] oriented Sr0.75Ba0.25Nb2O6 relaxor crystals have been studied by means of acoustic emission (AE) over a wide 20–400 °C temperature range. Both the Burns temperature, Td = 350 °C, and the intermediate temperature, T* = 183°C, and the susceptibility maximum temperature, Tm (59 °C on heating and 47 °C on cooling), have been successfully detected. Dependent upon the external electric field, the Tm exhibits a local minimum near 0.25 kV/cm accompanied by pronounced AE maximum in a manner which had recently been detected in Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 by Dul’kin et al. [Appl. Phys. Lett. 94, 252904 (2009)] and in Pb(Sc1/2Ta1/2)O3 by Dul’kin et al. [Phys. Rev. B 82, 180101(R) (2010)], whereas the T* increases monotonically, similar to that which had recently been revealed in BaTiO3 by Dul’kin et al. [Appl. Phys. Lett. 97, 032903 (2010)] with a rate of 7.5 K cm/kV. An observed Tm behavior is discussed from the point of view of the existence of the random electric field components along the [100] direction in Sr0.75Ba0.25Nb2O6 crystals.

Manifestation of Structural Disorder in the Polarization Kinetics of Non-Uniform TAAP and Relaxor SBN Ferroelectric Crystals

The comparative experimental analysis of the polarization reversal kinetics in non-uniform Te(OH)62NH4H2PO4(NH4)2HPO4 (TAAP) and relaxor Sr0.61Ba0.39Nb2O6 (SBN:61) crystals have been performed. Micro-scale studies of domain switching in conjunction with electrical measurements allowed us to establish a relationship between local properties of domain dynamics and macroscopic response; polarization hysteresis loop and switching currents. We investigated the microscopic features of 180 degree domain walls dynamics and relate its dynamics to the defect structure in both type of the crystals. The domain structure was studied by means of the nematic liquid crystal decoration method.