Defect structure and light‐induced scattering of Zr‐doped near‐stoichiometric Mn:Fe:LiNbO3 crystals grown by TSSG method

Near‐stoichiometric Mn:Fe:LiNbO₃ crystals doped with various concentration of ZrO₂ were grown by top seed solution growth (TSSG) method in the air atmosphere. The Zr concentration in the crystal was determined by inductively coupled plasma optical emission spectrometer. The defect structures were analyzed by means of ultraviolet‐visible and infrared transmittance spectra. The appearance of vibration peak at 3466 cm^‐1 in infrared spectra manifested that Li/Nb ratio in crystals approached to stoichiometric proportion. The fundamental absorption edge represented continuous red‐shift which was discrepancy with congruent doped LiNbO₃ crystals showed that doping ions possessed different location mechanism. The light‐induced scattering of the doped stoichiometric LiNbO₃crystals were quantitatively scaled via incident exposure energy. The results demonstrated that Zr(2 mol%):Mn:Fe:LiNbO₃ crystal had the weakest light‐induced scattering and the mechanism related to their defect structures was discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of near stoichiometric LiNbO3 single crystal

A near stoichiometric LiNbO₃ single crystal has been grown by the Czochralski method from a 58.5% Li melt hold in a large platinum crucible. High resolution X‐ray rocking curves of 30 0 and 0006 reflections indicated that the near stoichiometric LiNbO₃ crystal possesses the high structural quality. Compared with the congruent LiNbO₃, the near stoichiometric LiNbO₃ possesses shorter ultraviolet absorption edge, thus higher Li concentration. The OH^– infrared absorption band analyses showed that the Li concentration in the near stoichiometric LiNbO₃ crystal is higher than that in the congruent LiNbO₃ crystal. This result is in good agreement with that of the ultraviolet absorption edge. The electro‐optic (EO) coefficient γ₂₂ of the near stoichiometric LiNbO₃ crystal was measured to be 6.75 pm/V higher than that of congruent LiNbO₃ crystal. It also proves the near stoichiometric LiNbO₃ electro‐optic Q‐switched requires a low driving voltage and it is advantageous for the device performance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of LiNbO<Subscript>3</Subscript>:Er Crystals and concentration dependences of their properties

A series of lithium niobate (LiNbO₃) crystals of congruent and stoichiometric compositions, doped with erbium, have been grown under non-steady-state thermal conditions. A series of LiNbO₃:Zn crystals, nominally pure LiNbO₃ crystals of congruent and stoichiometric compositions, and a LiNbO₃:B crystal have also been grown. Both growth conditions and concentration dependences of physicochemical, ferroelectric, and structural characteristics of LiNbO₃:Er crystals are investigated. The growth regular domain microstructures and periodic nanostructures in LiNbO₃:Er crystals are analyzed by optical microscopy and atomic force microscopy (AFM). A comparative study of the optical homogeneity and photorefractive properties of LiNbO₃:Er crystals of congruent and stoichiometric compositions and the Raman spectra of LiNbO₃ crystals of different compositions is performed.     

Growth of near‐stoichiometric LiNbO3 crystals and Li2O contents determination

Two kinds of near‐stoichiometric LiNbO₃ crystals (SLN11 and SLN19) were grown by a flux pulling method from stoichiometric melt with addition of 11mol%K₂O and 19mol%K₂O, respectively. Compared with the congruent melting LiNbO₃, the ultraviolet absorption edges of two crystals shift towards shorter wavelengths, and the locations of the OH^‐ infrared absorption band have obvious change and the bandwidths become greatly narrower. From these experimental results, the Li₂O contents are determined indirectly to be about 49.6mol% for SLN11 and 49.9mol% for SLN19, respectively. The Li₂O content in SLN19 is very close to the ideal value of 50mol%. The coercive fields of two crystals were measured by the poling method at room temperature. A linear relationship between the Li₂O content and the coercive field was fitted. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Near‐stoichiometric LiNbO3:ZrO2 single crystal growth by micro pulling down method

Crack‐free, rod‐shaped single crystals of undoped and 0.5, 0.7 and 1.0 mol% ZrO₂‐doped LiNbO₃ with a near‐stoichiometric composition were grown by the micro‐pulling down (μ‐PD) method. The structural properties of the grown crystals were examined by powder X‐ray diffraction (XRD). Electron probe micro analysis (EPMA) of the near‐stoichiometric LiNbO₃ single crystals revealed the homogeneous incorporation of Zr ions. The change in the refractive index and IR transmission spectra of the grown crystals were examined as a function of the Zr concentration. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of domain structures in PZNT93/7 crystals by chemical etching

The domain structures in 0.93Pb (Zn_1/3Nb_2/3)O₃‐0.07PbTiO₃ (PZNT93/7) crystals were investigated by chemical etching technique. Original antiparallel 180° domains of size 20–40 μm were observed on the surface of as‐grown PZNT93/7 crystal. It was found the domain states are sensitive to the stress field induced by mechanical processing or impurities. As the composition of PZNT93/7 crystal was located near the morphotropic phase boundary, various domain configurations were observed. On the <001>‐oriented wafer, the etched a ‐ and c ‐domains revealed homogenous and island‐like patterns. The c ‐domains consist of upper and lower height regions corresponding to the tail and head of the polarization, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The color of langatate crystals and its relationship with composition and optical properties

Langatate crystals grown by the Czochralski method in 〈0001〉 and 〈01 1〉 directions both without subsequent annealing (from colorless to orange crystals) and with vacuum (colorless and pale‐green crystals) and air (orange crystal) annealing have been investigated by neutron diffraction, X‐ray diffraction and optical spectroscopy. The main types of point defects were compared with absorption bands: oxygen vacancies ‐ V_O^•• (0.35‐0.36 µm), the vacancies in the lanthanum position ‐ V_La‴ (0.29‐0.30 µm); the absorption band at 0.48‐0.49 µm is typical for the colored samples. The relationship between the X color coordinate (red component) and the oxygen contents has been obtained. The green color of the sample annealed in vacuum is due to the presence of Ta⁺³ ions in the La(Ta³⁺,Ga)O₃ phase that has the structural and geometric agreement with langatate structure. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure characteristics in near‐stoichiometric In:LiNbO3 single crystals grown by K2O‐flux method

With K₂O as flux, near‐stoichiometric In:LiNbO₃ (In:SLN) crystals with different indium contents were grown by the top seed solution growth (TSSG) method. Defect structure characteristics and the replacement principle of extrinsic ions were derived from X‐ray powder diffraction, differential thermal analysis (DTA), ultraviolet‐visible (UV) absorption and infrared (IR) spectrum measurement. Further analysis indicated that the threshold concentration of In₂O₃ in near‐stoichiometric LiNbO₃ crystals were about 1.1 mol%. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Domain structures and etching morphologies of lithium niobate crystals with different Li contents grown by TSSG and double crucible Czochralski method

Stoichiometric lithium niobate single crystals with different Li contents have been grown both by the top‐seeded solution growth (TSSG) method from potassium containing flux and by the double crucible Czochralski (DC Cz) method. Spectroscopic properties (e.g. the UV absorption edge, Raman linewidth) and the Curie temperature measurement have been used for the characterization of the crystal composition. The double crucible Czochralski method is found to be suitable for mass production of stoichiometric LiNbO₃ with Li content larger than 49.7 mol% and homogeneity of 0.03 mol%. The domain structures and etching morphologies on negative and positive c‐surface were also investigated by chemical etching method. A new domain structure of three‐fold symmetric sectors were observed in near‐stoichiometric LiNbO₃ grown by TSSG method. The straight line arrangement hillocks on negative c‐surface and the net‐like arrangement etch lines were observed and explained by stress etching mechanism. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improved blue photorefractive properties of near‐stoichiometric LiNbO3:Mn:Fe:Zr crystal

Near‐stoichiometric LiNbO₃ single crystal tri‐doped with ZrO₂, MnO and Fe₂O₃ was grown from Li‐riched melt by Czochralski method. The defect structures and composition of these crystals were analyzed by means of ultraviolet‐visible and infrared transmittance spectra. The appearance of 3466 cm^‐1 peak in infrared spectra showed that the crystal grown from Li‐riched melt was near stoichiometric. The photorefractive properties at the wavelength of 488 nm and 633 nm were investigated with two‐beam coupling experiment, respectively. The experimental results showed that the response speed and sensitivity were enhanced significantly and the high diffraction efficiency was obtained at 488 nm wavelength. This manifested that near‐stoichiometric LiNbO₃:Mn:Fe:Zr crystal was an excellent candidate for holographic storage. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and optical properties of near stoichiometric Ce:LiNbO3 crystals

The near sotichiometric Ce:LiNbO₃ (Ce:SLN) crystals were grown by the top seeded solution growth (TSSG) method by adding K₂O flux to Li₂O‐Nb₂O₅ melt. Their UV‐vis absorption spectra and IR spectra were measured and discussed to investigate their defect structure. The results showed that the grown crystals were near stoichiometric and Ce ions in the crystals located the Li site. Photorefractive properties of Ce:SLN crystals were studied by two‐wave coupling experiment. The results of the two‐wave coupling experiments of the crystals showed that as the CeO₂ doping concentrations increased, the diffraction efficiency increased, photoconductivity decreased and the writing time and erasure time increased. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Domain structure of Na1 − x LixNbO3 crystals

The domain structure of single-crystal and ceramic samples of Na_{1 ? x} Li_xNbO₃ solid solutions (at x ≤ 0.14) in the orthorhombic ferroelectric and antiferroelectric phases at room temperature is investigated by optical and electron microscopies and X-ray diffraction. The characteristic feature of the domain structure is the formation of 90° complexes consisting of laminar domains with a specific orientation relative to the lattice of the initial cubic phase. Consideration is given to the specific features in packing of these complexes and typical configurations of domains in the crystals. Observations revealed that the domain structure can involve 90°, 60°, 120°, and 180° boundaries, as well as (hhl) boundaries of the S type whose orientation depends on the cell distortion and changes with a variation in _x. The indices of these boundaries are determined. The density of 180° boundaries in the ferroelectric phase is very low compared to that of non-90° boundaries.     

Investigation of structural perfection and faceting in highly Er‐doped Yb3Al5O12 crystals

The undoped Yb₃Al₅O₁₂ (YbAG) single crystals and doped with 1.5, 10 and 30 at% erbium were grown by the Czochralski method. The YbAG crystals offer efficient emission of laser beam of 2.94 µm and 1.55 µm important for practical applications in communication and medicine. The crystals were investigated by various synchrotron X‐ray diffraction methods including white beam topographic methods, monochromatic beam topography and recording of the rocking curves. The experiments were performed at E2 and F1 experimental stations in HASYLAB. The investigations proved a good crystallographic perfection of the crystals, in most cases revealing only segregation fringes and growth facets. The crystallographic identification of the facets was performed together with direct evaluation of growth front radius from the transmission section topographs. Relative lattice parameter changes connected with erbium segregation were found to be less than 2 × 10^‐5 inside the segregation fringes and 8 × 10^‐5 in the facets. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and magnetic properties of the copper coordination polymer [Cu(µ ‐C2O4)(4‐aminopyridine)2(H2O)]n

In this paper, we consider various ways of crystal growth of the polymer [Cu(µ ‐C₂O₄)(4‐aminopyridine)₂(H₂O)]_n. Single crystals of the size of 1.5×1.5×0.2 mm³ have been grown by a slow diffusion technique from solutions of the monoammine copper complex and of the mixture of potassium oxalate and aminopyridine with the stoichiometric ratio. Magnetic susceptibility and ESR measurements have been performed on single crystals large enough for investigating anisotropic properties. The susceptibility can be well described within the model of a Heisenberg antiferromagnetic spin chain. The magnetic measurements reveal a small concentration of paramagnetic moments reflecting the high quality of the single crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure and optical damage resistance of In:Fe:Cu:LiNbO3 crystals with various [Li]/[Nb] ratios

In:Fe:Cu:LiNbO₃ crystals were grown in air by the Czochralski technique with various [Li]/[Nb] ratios of 0.946, 1.050, 1.200, and 1.380 in melt. Based on the ICP‐AES (inductively coupled plasma atomic emission spectrometry) analyzed results, the chemical formula of the triple‐doped In:Fe:Cu:LiNbO₃ crystals were obtained. It can be seen that the near‐stoichiometric ratio value is between 1.050 and 1.200 for our samples. The optical damage resistance of In:Fe:Cu:LiNbO₃ crystals was characterized by changes in light‐induced birefringence and it increases with the increasing of [Li]/[Nb] ratios. The dependence of the optical damage resistance on the defect structure of In:Fe:Cu:LiNbO₃ crystals is discussed in detail based on the obtained chemical formulas. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photorefractive Properties of Stoichiometric Lithium Niobate Single Crystals

The specific features of photorefractive light scattering in nominally pure stoichiometric (Li/Nb = 1) sin- gle crystals grown from a melt with 58.6 mol % Li₂O (LiNbO₃st) and in the stoichiometric single crystals grown from a melt of congruent composition in the presence of K₂O flux (LiNbO₃stK₂O) have been investi- gated. At an excitation power of 30 mW, LiNbO₃stK₂O single crystals are found to exhibit a stronger photo- refractive effect than LiNbO₃st single crystals.     

Spherulitic crystallization of β‐In2Te3 by physical vapour deposition

Different morphologies of indium telluride (In₂Te₃) including novel spherulites were crystallized using the physical vapour deposition (PVD) method, by varying the difference in the growth and source zone temperature (ΔT) of a dual zone horizontal furnace assembled indigenously. Whiskers and kinked needles of In₂Te₃were grown at ΔT = 250 K and 300 K respectively, maintaining the growth zone at 500 °C. At high supersaturation (Δ T = 400 K), spherulitic crystals were obtained. The stoichiometric composition of these crystals has been confirmed using energy dispersive analysis by x‐rays (EDAX). The structure of β‐In₂Te₃ spherulitic crystals is identified as zinc blende with lattice parameter a = 6.159 Å, from x‐ray diffraction (XRD) studies. The scanning electron microscope (SEM) images revealed the radial structure of the grown spherulites. The growth mechanism for the spherulitic crystallization of β‐In₂Te₃ crystals has been discussed based on the theoretical models. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

非对称扩散工艺制备近化学计量比钽酸锂晶体的研究

利用气相平衡输运法制备的近化学计量比钽酸锂晶体质量好,制备工艺简单,但受固体扩散速率低的影响,该方法较难制备大厚度晶体。本文基于钽酸锂晶体的扩散机制,采用待扩散晶片一侧为富锂气氛,另一侧为同成分气氛的非对称扩散工艺,对钽酸锂晶体进行了扩散处理,并对组分和畴反转电场进行表征。结果表明,非对称扩散工艺为反位钽离子的扩散提供了通道,提高了晶体中反位钽离子和锂离子的扩散速率,有利于制备大厚度近化学计量比钽酸锂晶体。     

Controllable synthesis of novel In2O3 nanostructures and their field emission properties

Three kinds of novel indium oxide (In₂O₃) nanostructures, namely, nanorods, nanoflowers and nanowhiskers were synthesized on silicon substrate via a simple vapor‐phase transport method under atmospheric pressure. The In₂O₃nanostructures were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy‐dispersive X‐ray spectrometer (EDS) spectrum. The Raman spectra of these nanostructures showed four sharp scattering peaks centered at 308, 365, 522, and 628 cm^‐1, whose position and intensity were characteristic of standard Raman spectra for In₂O₃. The Room‐temperature photoluminescence (PL) spectra showed visible emissions centered around 576, 592, and 624 nm. Field emission measurements demonstrated that the nanoflowers possessed the best performance with a turn‐on field of 3.54 V/µm and a threshold field of 9.83 V/µm. And the field enhancement factors of these nanostructures are high enough for the application of field emission display devices. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Increased optical damage resistance of Zr:LiNbO3 crystals

Zr: LiNbO₃ crystals has been grown. The crystal composition and phase are analyzed by X‐ray diffration. The optical damage resistance ability of Zr: LiNbO₃ crystals is studied by the Sénarmont compensation method and the transmitted beam pattern distortion method. The saturated value of the birefringence change of 6 mol% Zr: LiNbO₃ crystal is 1.01×10^‐4, which is seven times smaller than that of congruent pure LiNbO₃ crystal. The results of UV‐Visible and IR absorption spectra of Zr: LiNbO₃ crystals powerfully confirm that the optical damage resistance threshold concentration of the Zr⁴⁺ ions doped in LiNbO₃ crystals is about 6 mol% in the melt. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)