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1.
Xu Jiayue Fan Shiji Lin Yafang Xu Xuewut 《Progress in Crystal Growth and Characterization of Materials》2000,40(1-4):137-144
Transparent KLN crystals 10mm in diameter and 25 to 45mm in length have been grown by the modified vertical Bridgman technique from different melts in the range of 3035mol% K2O, 1723mol% Li2O and 4350mol% Nb2O5. The growth conditions are a growth rate of less than 0.25 mm/hr, temperature gradient in solid-liquid interface of 23 °C/mm and growth direction of <110>. As-grown KLN crystals have tetragonal tungsten bronze structure. Most of the as-grown crystals do not crack when cooling through the paraelectric/ferroelectric phase transition. 180° domain structures are observed after the KLN crystal was etched in boiling 2HNO3:Hf. Dielectric properties and transmission spectrum of the as-grown KLN crystals are measured. 相似文献
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I. V. Kubasov A. M. Kislyuk A. S. Bykov M. D. Malinkovich R. N. Zhukov D. A. Kiselev S. V. Ksenich A. A. Temirov N. G. Timushkin Yu. N. Parkhomenko 《Crystallography Reports》2016,61(2):258-262
The bidomain structures produced by light external heating in z-cut lithium niobate and lithium tantalate single crystals are formed and studied. Interdomain regions about 200 and 40 μm wide in, respectively, LiNbO3 and LiTaO3 bidomain crystals are visualized and studied by optical microscopy and piezoresponse force microscopy. Extended chains and lines of domains in the form of thin layers with a width less than 10 μm in volume, which penetrate the interdomain region and spread over distances of up to 1 mm, are found. 相似文献
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A method of construction of the spatial distribution of the piezo-optic effect in crystals is proposed. A particular case of this method is the known technique of construction of indicator surfaces of the piezo-optic effect. The essence of the proposed method consists in determining the difference in the radius vectors of the optical indicatrix perturbed by stress and the free optical indicatrix. It is shown that this difference in the radius vectors is mathematically identical to the law of transformation of the piezo-optic tensor during the rotation of the coordinate system. 相似文献
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W. Bollmann 《Crystal Research and Technology》1983,18(9):1147-1149
Investigations of the OH− ion incorporation into LiNbO3 crystals and the comparison of calculated and measured densities show that undoped congruent lithium niobate crystals contain Li+ and O− − ion vavancies O and Li+. If really present, stacking faults are of inferior importance. The good agreement of the absorption edges of stoichiometric and of 2.7 mol% MgO containing congruent lithium niobate crystals is explained by the occupance of all oxygen sites within these crystals. 相似文献
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Crystallography Reports - A real structure of lithium niobate single crystals has been studied by the etching method. A relationship between the real structure and the optical inhomogeneity... 相似文献
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H. T. Li Y. X. Fan F. Y. Guo S. H. Zhang L. C. Zhao 《Crystal Research and Technology》2007,42(10):1014-1017
Cu:LiNbO3 crystal and Fe:Cu:LiNbO3 crystals were grown by the Czochralski method from congruent melt. The OH‐ absorption spectrum of doped lithium niobate crystals was measured. The photorefractive properties of doped crystals were studied by the two‐wave coupling method. The results of the two‐wave coupling experiments showed that as the concentration of doping ions increased, the diffraction efficiency and the dynamic range enhanced, the holographic response time shortened. The recording time of Fe(0.10wt%): Cu(0.10wt%): LiNbO3 crystal is only a tenth of that of Cu(0.05wt%): LiNbO3 crystal. Among all samples, the dynamic range of the Fe(0.10wt%): Cu(0.10wt%): LiNbO3 crystal was the most largest (up to 40.78). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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The ferroelectric phase of potassium lithium niobate K3Li2−xNb5+xO15 (KLN) is a very promising material for the conversion of infrared light to light in the visible region. However, growing of single crystals is known to be complicated due to the considerable anisotropy of the growth rate and the thermal expansion behaviour. The single crystals of KLN, Mg2+‐doped KLN, as well as the mixed crystals of potassium lithium tantalate niobate K3Li2(Nb1−xTax)5O15 (KLTN) were grown by the Czochralski technique. The chemical analyses of the samples were performed by atomic absorption spectroscopy (AAS) and X‐ray fluorescence analysis (XRF). The element concentrations along the single crystals were measured by the electron microprobe analysis (EMPA) to clarify the segregation phenomena in the grown crystals. The elements distribution coefficients were also calculated. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Absorption spectra temperature dependence of LiNbO3 doped with the Cr-, Mn-, Fe, Co-, Ni- and Cu-irons is studied. Band gap variation of the doped lithium niobate against impurity, temperature and light polarization direction is determined. 相似文献
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On the basis of precise X-ray diffraction study of lithium niobate single crystals of congruent composition and four zinc-doped (at 2.8, 5.2, 7.6, and 8.2 mol %) crystals, structural conditionality of the threshold concentrations of the dopant has been established. At these concentrations, the mechanism of zinc incorporation into crystal changes. As the zinc concentration increases, this element first substitutes excess niobium, localized in lithium positions, with a simultaneous decrease in the number of vacancies in these positions. Then zinc substitutes lithium with formation of new lithium vacancies. When a certain limit on the number of vacancies is reached, zinc begins to substitute niobium in its main positions. This process is naturally accompanied by a decrease in the number of vacancies to their complete disappearance and formation of a self-compensating crystal. The character of the dependence of the crystal physical properties on the dopant concentration changes specifically when the impurity concentration passes through the threshold values. 相似文献
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《Journal of Non》2006,352(23-25):2395-2398
Cr3+-doped stoichiometric LiNbO3 crystals were grown and detailed spectroscopic investigations were performed. The samples are characterized by extremely low frequency factor of the luminescence thermal quenching. Its numerical value 1.7 × 108 s−1 is about 104 times lower than in crystals of lithium-aluminum fluorides. Under such conditions, radiative transitions of Cr3+ ions compete successfully with non-radiative ones, resulting in a relatively high quantum yield of the broadband luminescence at room temperature. The quenching of luminescence is counteracted by the effect of the dynamic removal of the radiative transition exclusion, and as a result, Cr3+ radiative lifetime in LiNbO3 decreases from 8 to 4 μs when temperature grows up from 77 to 300 K. Therefore quantum yield of the broadband luminescence at room temperature is not 5–10%, as reported previously, but about 30%. The results obtained in the present study show the stoichiometric lithium niobate doped with Cr3+ ions to be a potential active media for tunable lasers. 相似文献
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The distributions of edge dislocations and residual mechanical stresses in BaxSr1-xNb2O6 (BSN) crystals are investigated and the explanation of the nature of the “growth column” is proposed. The “growth column” is a defect zone going through all of the crystal and usually repeating in its cross-section the contour of the seed crystal. The “growth column” boundary is the closed contour with extremely high edge dislocation density. These dislocations are connected with thermal stresses due to seed-melt contact or abrupt crystal widening. Under proper crystal seeding and widening conditions one can obtain the BSN crystals with dislocation densities less than 10 cm−2 and without the “growth column”. The method of chemico-mechanical polishing of BSN crystals not forming a defect layer on the surface of the crystals have been developed. The high temperature diffusion annealing is shown to eliminate the growth striae in BSN crystals. 相似文献
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N. V. Sidorov M. N. Palatnikov A. A. Yanichev A. A. Gabain O. V. Makarova O. Yu. Pikul’ 《Crystallography Reports》2014,59(5):724-731
Methods of Raman spectroscopy, laser conoscopy, optical microscopy, and electron spin resonance have been used to study the photorefractive properties and structural and optical homogeneity of the following lithium niobate (LiNbO3) crystals: nominally pure crystals of congruent composition (LiNbO3con); LiNbO3:Cu[0.015 wt %] crystals grown from a melt of congruent composition and nominally pure crystals of stoichiometric composition grown from a melt with 58.6 mol % Li2O (LiNbO3st). A small deformation of optical indicatrix and regular microdomain structures of fractal type are revealed for the LiNbO3:Cu[0.015 wt %]; the microdomain structures may be due to the nonuniform impurity incorporation into the structure. It is shown that oxygen octahedra in the LiNbO3:Cu[0.015 wt %] crystal are deformed in comparison with the octahedra in LiNbO3st and LiNbO3con crystals and that the main and impurity cations are clusterized along the polar axis. It is established that the LiNbO3:Cu[0.015 wt %] crystal exhibits photorefractive properties not only due to the presence of intrinsic defects with localized electrons, as in the case of LiNbO3st, but also due to the charge exchange in copper cations (Cu2+ → Cu+) under illumination. 相似文献
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B. Suresh Kumar M. R. Sudarsana Kumar K. Rajendra Babu 《Crystal Research and Technology》2008,43(7):745-750
Single crystals of pure and lithium substituted L‐alanine are successfully grown by slow evaporation method at constant temperature of 32°C. The effect of lithium dopant on crystal properties has been studied. Powder and single crystal XRD analysis confirms the structure and change in lattice parameter values for the doped crystals. The crystals were characterized by solubility studies, density, melting point measurements, FTIR and UV‐Vis‐NIR techniques. Thermal and mechanical stability of crystals were tested by TGA/DTA and micro hardness analysis. NLO activity of the crystals is found to be increased in the presence of lithium ions. The dielectric constant and dielectric loss of the crystals were studied as a function of frequency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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O. G. Vlokh B. G. Mytsyk A. S. Andrushchak Ya. V. Pryriz 《Crystallography Reports》2000,45(1):138-144
For the first time, the “indicative” surfaces of the constants of the piezooptic effect and their stereographic projections have been constructed with due regard for crystal elasticity for lithium niobate crystals described by the symmetry class 3m. The comparative analysis of these surfaces and the corresponding surfaces of the true piezooptic effect has been performed. 相似文献
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V. M. Voskresenskii O. R. Starodub N. V. Sidorov M. N. Palatnikov 《Crystallography Reports》2017,62(2):205-209
The processes occurring upon the formation of energetically equilibrium oxygen-octahedral clusters in the ferroelectric phase of a stoichiometric lithium niobate (LiNbO3) crystal have been investigated by the computer modeling method within the semiclassical atomistic model. An energetically favorable cluster size (at which a structure similar to that of a congruent crystal is organized) is shown to exist. A stoichiometric cluster cannot exist because of the electroneutrality loss. The most energetically favorable cluster is that with a Li/Nb ratio of about 0.945, a value close to the lithium-to-niobium ratio for a congruent crystal. 相似文献
18.
T.‐C. Rdel D. Wang D. S. Su M. Lerch A. Prokofiev K. D. Luther W. Assmus 《Crystal Research and Technology》2006,41(10):950-954
The aim of this work is the preparation of nitrogen‐doped single crystals of cation‐stabilized zirconia. Thin plates of these crystals were nitrided in a graphite heated resistance furnace with nitrogen as reaction gas. Several dwell times and reaction temperatures were tested and their effect on the amount of incorporated nitrogen is investigated. During nitridation at high temperatures a rock salt‐type ‘ZrN’ layer grows on the surface, leading to the destruction of the crystal. In contrast to the fluorite‐type bulk material, which can be described as a fast anion conductor, the surface layer shows electronic conductivity. For possible applications of the bulk material (solid electrolyte) the formation of the surface layer must be avoided. Therefore, the interface between surface epilayer and bulk material was investigated in detail by electron microscopy methods. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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H. C. Zeng T. C. Chong L. C. Lim H. Kumagai M. Hirano 《Journal of Crystal Growth》1996,160(3-4):289-295
The study of meniscus effects on the directional growth of single crystals of potassium niobate (KNbO3) with a [110]pc oriented seed by the top-seeded-solution-growth technique has been described. The directional growth of KNbO3 single crystals has been illustrated for different crystallographic orientations of the crystal. Experimental results show that the shape of the solution flux meniscus, which is determined by a number of growth parameters, has a significant effect on growth rates on different 100pc, 010pc and 001pc type surfaces. Findings based on this work enable one to select a dominant growth direction and hence to engineer the geometrical shaping of resultant KNbO3 single crystals through careful control of growth parameters. Maximum crystal dimensions for the grown KNbO3 along [100]pc and [001]pc achieved in this work are 34.0 and 31.2 mm, respectively. 相似文献