Growth,structural and optical properties of 12%‐deuterated KDP crystals

K(D_0.12H_0.88)₂PO₄ crystals were chosen to be used for quadratic nonlinear medium of wideband frequency doubling at 1 μm. A key limitation on this application is that little information can be found in the previous reports. In this work, growth as well as structural and optical properties of this crystal were investigated in detail. Experimental results in comparison with KDP indicate that lattice parameter along a‐axis changes much more than lattice parameter c and infra‐red absorption edge shift by 0.08 μm accompanied with increasing of transmittance in the whole region. With the introduction of deuterium atom, peak of ν₁(PO4) shifts to lower wave number and transverse stimulated Raman scattering was effectively suppressed. Extra‐ordinary and ordinary indices were also measured as function of wavelength. Good crystalline perfection and great performance of damage threshold also indicate that 12%‐DKDP is an appropriate choice in the application of wideband frequency doubling at 1 μm.     

Growth and etching of calcite crystals

Single crystals of calcite (CaCO₃) have been grown by the method employed by GRUZENSKY , using an aquoeus solution of CaCl₂ and a solid (NH₄)₂SO₃, The chemical reaction takes place according to the following equation: CaCl₂ + (NH₄)₂SO₃ CaCO₃ + 2 NH₄Cl The crystals grown by this method are about 0.2 to 0.8 mm in edge dimensions. Synthetic calcite crystals have been cleaved along (100) planes and the cleavage surfaces have been studied by multiple beam interferometry. The interferograms have revealed that the cleavages are quite flat. The cleavage faces have also been chemically etched and the etch patterns studied optically. By etching a cleavage successively for three different periods it was found that the bottoms of the point-bottomed pits follow a linear etch path. By etching a cleavage pair, one face in one etchant and the other face in a different etchant and by comparing the etch patterns produced, before and after polishing a cleavage face it has been shown that the etch pits nucleate at the sites of dislocations in the crystal. The etch patterns have also been compared with those produced on the cleavage faces of natural crystals. The density of dislocations in the syntheitc calctie crystals was generally less than the density of dislocations in the natural calcite crystals. The implications have been discussed.     

Growth,etching morphology and spectra of LiAlO2 crystal

γ‐LiAlO₂ single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X‐ray rocking curve and chemical etching. The effects of air‐annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO₂ were also investigated in detail. The results show that the as‐grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7‐22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0×10³ cm^–2. The VTE‐treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air‐annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and etching of anhydrous diglycine sulfate single crystals

Single crystals of anhydrous diglycine sulfate are grown at constant temperature by evaporation method. The crystals are grown at various temperatures and their growth rate is determined. A chemical etchant for dislocation studies is reported. The perfection of the crystals grown at various temperatures has been studied using etching technique. It is found that the crystals contained inclusions of the mother liquid. The crystals grown below 28° are almost free of inclusions and the dislocation density is also low.     

Dielectric properties of betaine phosphite and deuterated betaine phosphite films

Polycrystalline films of betaine phosphite (BPI) and deuterated BPI have been grown by evaporation on LiNbO₃, α-SiO₂, α-Al₂O₃, and NdGaO₃ substrates. These films consist of large single-crystal blocks in which the polar axis (b) lies in the substrate plane. The results of studying the dielectric properties of the films using interdigital electrodes, X-ray diffraction, and block images in a polarized-light microscope in reflection are reported. The film transition into the ferroelectric state at T = T _c is accompanied by strong anomalies of the capacitance of the film/interdigital structure/substrate structure. The deuteration of BPI films leads to an increase in their temperature T _c: from T _c = 200 K for BPI-based structures to T _c = 280 K for structures with a high degree of deuteration (d ∼ 90%).     

Decoration of growth and dissolution steps on the surfaces of L-arginine phosphate monohydrate crystals

Observations of decoration of growth and dissolution steps on the {100} surfaces of non-linear optical L-arginine phosphate monohydrate (LAP) crystals during their withdrawal through an n-hexane layer placed above its supersaturated and undersaturated solutions are described. This is the first report of decoration of growth or dissolution steps on the surfaces of crystals at or near room temperature in a liquid medium by the crystallizing or dissolving material.     

Growth and selective etching studies on NaBrO3 crystals

Surface studies on (111) faces of sodium bromate crystals grown from aqueous solution show the presence of growth steps. A new etchant consisting of a mixture of 8 parts of glacial acetic acid and 2 parts of formic acid, to which 3 mg/cc of cupric nitrate is added, reveals the dislocation sites on (111) faces of these crystals. The etching action on (111) and (111 ) faces is different. Different microhardness values are recorded on (111) and (111 ) faces of these crystals. The difference in etching action as well as in microhardness values on (111 ) and (111) faces is discussed.     

Acoustic study of elastic properties,dislocation damping and plasticity of crystals

The results of acoustic studies of elasticity and dislocation inelasticity of crystals are presented. Regularities of elastic anisotropy variation with ionicity of bonds in A_NB_8-N crystals have been considered. Amplitude dependences of ultrasound damping supply the information on dislocation structure and dislocation — to point defect interaction. Oscillation of dislocations during internal friction measurements are compared to their translation motion at the onset of plastic flow.     

Growth of octacalcium phosphate and dicalcium phosphate dihydrate crystals in silica gels

The crystallization of octacalcium phosphate (OCP) and dicalcium phosphate dihydrate (DCPD) have been studied at ambient temperature in silica gel using double diffusion system. The first stage of evolution of the OCP spherulites as well as their growth have been observed by optical microscopy. The growth rate of the OCP spherulites under stable external conditions was constant. The formation of DCPD crystals has been observed in the last stages of experiments.     

Optical properties of bismuth in germanate,borax and phosphate glasses

Absorption, emission, excitation spectra and quantum efficiencies of luminescence of bismuth were obtained in germanate, borax and phosphate glasses. Decay times were measured for fluorescence of bismuth in germanate glass at room temperature and liquid air temperature. A non-exponential decay of fluorescence at room temperature is observed. A thermal equilibrium between the ³P₁ and ³P₀ states is discussed. The dependence of fluorescence intensity and decay times on temperature is presented. The amount of covalency between bismuth and glass matrix was calculated from the nephelauxetic effect.     

Growth of GaN single crystals with extremely low dislocation density by two-step dislocation reduction

We have discovered a mechanism which can significantly reduce the dislocation density during the growth of GaN single crystals in the Na flux method. The significant reduction of the dislocation density occurs in the later stage of LPE growth, rather than solely at the seed-LPE interface for which we have already reported evidence indicating the presence of bundling dislocations. The two-step dislocation reduction is the key in achieving extremely low dislocation density using this method.     

Electrical properties of phosphate glasses

The electrical properties of glasses in the Na₂OP₂O₅, Ag₂OP₂O₅ and (1?x)Na₂OxAg₂OP₂O₅ systems have been measured over a range of temperature and composition.The properties of the Na₂OP₂O₅ and Ag₂OP₂O₅ glasses have been compared within the phosphate system as well as with silicate glasses. The silver-containing glasses show higher conductivity and lower temperature coefficients when compared with the sodium-containing glasses. A maximum in the room temperature resistivity of the (1?x)Na₂O?xAg₂O?P₂O₅ system was found around the mole ratio of 0.16:0.84 Ag₂O:Na₂O, indicating a mixed-alkali effect. A similar effect was seen in the tan δ, but not in the T_g-against-composition plots. A linear relationship was noted for the tan δ-versus-log₁₀ (resistivity) plot, as has been seen in other glass-forming systems.     

Composition,microstructure and mechanical properties of chemically vapour-deposited tantalum

The paper reports the results of a structural investigation of C.V.D. tantalum, which had been deposited on a silica substrate. Deposits at 1000°C were high impurity powders or flakes, at 1100°C (normal deposition temperature) foil-like, these containing much lower silicon contents, being concentrated near the substrate and coming from there by diffusion. The overall silicon content is reported to be due to other kinds of mass transport (i. e. vapour phase transport) and reactions (e.g. Ta with quartz). — Details on the structure and hardness of the Ta layers are given.     

Iron redox equilibrium, structure and properties of zinc iron phosphate glasses

Iron redox equilibrium, structure and properties were investigated for the 10ZnO-30Fe₂O₃-60P₂O₅ (mol%) glasses melted at different temperatures. The structure and valence states of the iron ions in these glasses were investigated using Mössbauer spectroscopy, Raman spectroscopy and differential thermal analysis. Mössbauer spectroscopy indicated that the concentration of Fe²⁺ ions increased in the 10ZnO-30Fe₂O₃-60P₂O₅ (mol%) glass with increasing melting temperature. The Fe²⁺/(Fe²⁺ + Fe³⁺) ratio increased from 0.18 to 0.38 as the melting temperature increased from 1100 to 1300 °C. The measured isomer shifts showed that both Fe²⁺ and Fe³⁺ ions are in octahedral coordination. It was shown that the dc conductivity strongly depended on Fe²⁺/(Fe²⁺ + Fe³⁺) ratio in glasses. The dc conductivity increases with the increasing Fe²⁺ ion content in these glasses. The conductivity arises from the polaron hopping between Fe²⁺ and Fe³⁺ ions which suggests that the conduction is electronic in nature in zinc iron phosphate glasses.     

Optical,mechanical and thermal properties of p‐bromoacetanilide

Solubility and metastable zonewidth were estimated for p‐Bromoacetanilide. Employing slow evaporation method crystals of size 22x17x6 mm³ and 38x25x10 mm³ were grown at a constant temperature of 40°C and room temperature respectively from methanol solution. The cell dimensions were obtained by single crystal X‐ray diffraction study. The placement of protons was identified from NMR spectral analysis. UV‐Visible and fluorescence spectral analyses were carried out for the grown crystals. Vickers microhardness test was performed on the prominent (110) of the as grown crystal. Thermogravimetric and differential scanning calorimetric studies were carried out to determine the thermal properties of the grown crystal. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and structural, optical, and electrical properties of zincite crystals

An X-ray diffraction study of ZnO crystals grown by the hydrothermal method has revealed reflections that give grounds to assign them to the sp. gr. P3 rather than to P6₃ mc. The distribution of Zn1, Zn2, O1, and O2 over structural positions, along with vacancies and incorporated zinc atoms, explains the dissymmetrization observed in terms of the kinetic (growth) phase transition of the order-disorder type, which is caused by ordering Zn and O atoms over structural positions. The color of crystals of refined compositions (Zn_0.975□_0.025)Zn _i(0.015)(O_0.990□_0.010) (green) and (Zn_0.965□_0.035)Zn _i(0.035)O (bright green) is related to different oxygen contents, which is confirmed by the results of electron probe X-ray microanalysis and absorption spectroscopy. The degree of the structural quality of crystals, their resistivity, and activation energy are also related to oxygen vacancies.     

Structural and optical properties of vapour‐etching based porous silicon

The structural and optical properties of porous silicon (PS) layers prepared by Vapour‐Etching (VE) of moderately and heavily boron‐doped Si substrates are investigated. The VE technique produces rough PS layers that are essentially formed of interconnected cluster‐like structures. Optical investigations indicate that this surface roughness enables the PS layers to be used as antireflection coatings in silicon based devices. These optical characteristics are investigated by optical reflectivity and light scattering. The local chemical state and the microstructure of the PS layers are studied by electron energy loss spectroscopy (EELS) in transmission electron microscopy (TEM), and are correlated to the red photoluminescence (PL). TEM studies point out that the cluster‐like interconnected structures are composed of luminescent nanocrystallites. PL measurements display that both quantum confinement and surface passivation determine the electronic states of the silicon nanocrystallites. The complex dielectric function is calculated from the experimental single‐scattering distribution spectrum using a Kramers Kronig analysis. The first resonance peak in the imaginary part is observed at 2.3 eV; two other broadened features appear at 4.7 and 8.8 eV. The latter is generally related to an interface plasmon resulting from the silicon‐silicon oxide interface. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,properties, and structure of potassium titanyl phosphate single crystals doped with hafnium

Single crystals of potassium titanyl phosphate doped with hafnium are grown by spontaneous flux crystallization. Their physical properties are studied, and the structure of three KTi_{1 − x} Hf _x OPO₄ crystals (x = 0.01, 0.03, and 0.12) is determined. In the crystals studied, hafnium mostly occupies the second titanium position. The doping of KTP crystals with hafnium results in an elongation of K-O bonds in the potassium polyhedra and, as a consequence, in a considerable (by approximately 180°C) decrease in the temperature of ferroelectric phase transition. The magnitude of anomalous permittivity substantially decreases. The electrical conduction in the specimens studied decreases by approximately half an order of magnitude in the low-temperature region but remains almost unchanged in the high-temperature region. Even at minor concentrations, the presence of a hafnium additive in the specimens considerably (by 35%) enhances the intensity of the second harmonic generation of laser radiation.     

Growth of large crystals of deuterated tetrathiafulvalene tetracyanoquinodimethan (TTF-TCNQ-d8)

Large single crystal platelets of TTF-TCNO-d₈ up to 30 × 6 × 0.7 mm³ were grown from acetonitrile by the diffusion method at 36°C.