Showing papers in "Crystal Research and Technology in 1999"
TL;DR: Theoretical analysis of the micro-pulling-down process and the practice of micro pulling-down growth are discussed in this article, along with growth properties of fiber-crystals.
Abstract: 1 What Do We Want With Fiber Crystals? An Introductory Overview.- 2 Fundamentals of Growth Dynamics of the ?-Pulling Down Method.- 3 Theoretical Analysis of the Micro-Pulling-Down Process.- 4 Practice of Micro Pulling Down Growth.- 5 Crystal-Chemistry and Fiber Crystal Growth of Optical Oxide Materials.- 6 Oxide Eutectic Crystals for High-Temperature Structural Application.- 7 Oxide Fiber Crystals Grown by ?-PD and LHPG Techniques.- 8 Growth of Micro and Bulk Crystals by Modified Micro-PD and their Properties.
171 citations
TL;DR: In this article, a comprehensive review is given on experimental studies of small particles with fivefold symmetry accompanied by an in-depth theoretical description of their characteristics and computer modeling, including the cases of uniform and nonuniform deformations (disclination model), stability and relaxation of elastic stresses in pentagonal particles and needle-like crystals.
Abstract: A comprehensive review is given on experimental studies of small particles with fivefold symmetry accompanied by an in-depth theoretical description of their characteristics and computer modeling. The cases of uniform and nonuniform deformations (disclination model), stability and relaxation of elastic stresses in pentagonal particles and needle-like crystals, models of their formation are discussed.
150 citations
TL;DR: In this paper, rare earth doped scandia and yttria have been grown from rhenium crucibles by the Czochralski technique, to the best of our knowledge.
Abstract: Rare earth doped scandia and yttria have been grown from rhenium crucibles by the Czochralski technique - to our knowledge for the first time. Spectroscopic data of Yb:Sc 2 O 3 are presented in detail and first laser experiments are reported. Despite the rather high crystal losses of about 2 % a slope efficiency of 37 % was obtained under diode pumping.
148 citations
TL;DR: The perovskite (TbAlO 3, TAP) with a congruent melting point of 1930°C is the most stable phase in the binary system as discussed by the authors.
Abstract: Attempts to grow terbium aluminium garnet (Tb x Al s O 12 , TAG) by the CZOCHRALSKI method lead to crystals of millimeter scale. Larger crystals could not be obtained. DTA measurements within the binary system showed that TAG melts incongruently at 1840°C. The perovskite (TbAlO 3 , TAP) with a congruent melting point of 1930°C is the most stable phase in this system. The region for primary crystallization of TAP covers the chemical composition of TAG and suppresses the primary crystallization of the terbium aluminium garnet.
105 citations
TL;DR: In this article, the vibrational frequencies of chalcopyrite type compounds are derived from the zone center or zone boundary vibrations of the sphalerite lattice assuming similar bonding and normal co-ordinates in all compounds investigated.
Abstract: To obtain a sound basis for calculations of the lattice dynamics of chalcopyrite type compounds the literature data for the vibrational frequencies of 14 chalcogenides and 8 pnictides crystallizing in this structure are critically analysed. This is done by introducing frequency ratios of those frequencies which can be derived from zone centre or zone boundary vibrations of the sphalerite lattice presuming similar bonding and normal co-ordinates in all compounds investigated. Based on the reliable spectra vibrational frequencies have been calculated for those compounds which have not yet been investigated or for which the results given in the literature are uncertain.
102 citations
TL;DR: In this paper, the thermal expansion coefficients along a- and c-axis are α 1 = 2.2 × 10 -6 /K, and α 3 = 8.4 × 10 −6/K respectively.
Abstract: Nd:YVO 4 crystal has been grown by Czochralski method. The data of thermal expansion and specific heat have been measured. The thermal expansion coefficients along a- and c-axis are α 1 = 2.2 × 10 -6 /K, and α 3 = 8.4 × 10 -6 /K respectively. The specific heat is 24.6 cal/mol K at 330 K. The large anisotropy along c- and a-axis of thermal expansion coefficients is explained by the structure of YVO 4 crystal. 921 mW output laser at 1.06 μm has been obtained with a 3 mm × 3 mm × 1 mm crystal sample when pumped by 1840 mW cw laser diode, and the slope efficiency is 55.5%.
75 citations
TL;DR: In this article, the microhardness of Larginine hydrobromide monohydrate (LAHBr) has been investigated and the work hardening index n for the three planes is greater than 1.6 which indicates that LAHBr is a soft crystal.
Abstract: Vicker's microhardness study of (100), (010) and (001) faces of a non-linear optical crystal, L-arginine hydrobromide monohydrate (LAHBr)have been reported.(100) plane is found to be the weakest plane. It has been observed that the microhardness decreases with increasing load for the three crystal planes. The microhardness behaviour have been explained successfully with the help of the PSR model proposed by Li and Bradt. Work hardening index n for the three planes are found to be greater than 1.6 which indicates that LAHBr is a soft crystal.
74 citations
TL;DR: In this paper, the optical properties of these films are investigated in the entire UV-Visible-IR region (0.2 - 10 mikrom). The observed absorption edge lies at 3.65 eV for undoped tin oxide and on doping it shifts towards higher energies, which is due to the Moss-Burstein effect.
Abstract: Undoped, fluorine doped and antimony doped tin oxide films are prepared on quartz plates by Spray pyrolysis technique. The films grown at the optimum substrate temperature with different doping levels have been chosen for this study. Optical properties of these films are investigated in the entire UV-Visible -IR region (0.2 - 10 mikrom). The observed absorption edge lies at 3.65 eV for undoped tin oxide and on doping it shifts towards higher energies, which is due to the Moss - Burstein effect. For fluorine doping depending upon the fluorine concentration, the absorption edge lies in the range 3.9 - 4.14 eV and for antimony doping it lies in the range 3.82 - 4.1 eV. In the undoped tin oxide films the direct allowed transition occurs at 4.02 eV and indirect allowed transition occurs at 2.43 eV, whereas for fluorine doped tin oxide and antimony doped tin oxide films, the direct allowed transitions occur in the range 4.18 - 4.28 and 4.13 - 4.22 eV respectively and the indirect allowed transitions occur in the range 2.63 - 2.73 and 2.54 - 2.65 eV respectively. Optical properties near the plasma edge have been analyzed using Drude's theory. The dependence of effective mass on carrier concentration has been explained on the basis of nonparabolicity of the conduction band. The shift in the fermi energy, calculated on the basis of energy dependent effective mass, is consistent with the measured shift in the absorption edge.
65 citations
TL;DR: In this paper, the influence of oxygen pressure and substrate temperature on the structure and optical properties of the zinc oxide films were systematically investigated and optimised the deposition parameters to prepare single phase zinc oxide film with preferred (002) orientation.
Abstract: Zinc oxide films were deposited on glass substrates in argon and oxygen atmosphere by dc reactive magnetron sputtering using a metallic zinc target. The influence of oxygen pressure and substrate temperature on the structure and optical properties of the films were systematically investigated and optimised the deposition parameters to prepare single phase zinc oxide films with preferred (002) orientation. At an optimum oxygen pressure of 1x10 -3 mbar and substrate temperature of 663 K, the films exhibited an optical transmittance of 83% with a band gap of 3.28 eV.
52 citations
TL;DR: In this paper, an ultrasonic technique is used to develop a method based on the measurement of both ultrasonic velocity and temperature of the supersaturated media for the on-line determination of supersaturation.
Abstract: An ultrasonic technique is used to develop a method based on the measurement of both ultrasonic velocity and temperature of the supersaturated media for the on-line determination of the supersaturation. It is demonstrated by the example of aqueous K 2 SO 4 solution in a seeded batch crystallizer. The feasibility of this technique was investigated using a commercial available sensor. The experimental measurements for the desupersaturation versus time trajectory proved that this technique can be successfully employed to measure supersaturation with sufficient accuracy and precision. Such sensor is preferred in the on-line application due to its fast response and the availability to be applied directly in the slurries without any need to the solid-liquid separation.
46 citations
TL;DR: The results on growth mechanism of GaAs layers by epitaxial lateral overgrowth (ELO) technique from the liquid phase are reviewed in this article, in particular, effects of melt supersaturation, seed orientation, density of surface steps and growth temperature on properties of ELO layers are discussed.
Abstract: The results on growth mechanism of GaAs layers by epitaxial lateral overgrowth (ELO) technique from the liquid phase are reviewed. In particular, effects of melt supersaturation, seed orientation, density of surface steps and growth temperature on properties of ELO layers are discussed. It is shown that the results obtained are not a specific attribute of LPE ELO growth of GaAs layers on GaAs substrates but represent a more general phenomena encountered during the ELO growth of other epitaxial systems.
TL;DR: In this article, an eutectic gallium-indium alloy is studied in a horizontal Bridgman furnace geometry, where different temperature gradients are applied to solidify and melt the alloy while observing in-situ the interface morphology and the chemical segregation in the melt and in the solid as well.
Abstract: Eutectic gallium-indium is studied in a horizontal Bridgman furnace geometry. Differential temperature gradients are applied to solidify and melt the alloy while observing in-situ the interface morphology and the chemical segregation in the melt and in the solid as well. Upon cooling, a wedge-type indium-rich mushy zone develops at the cold wall. The melt is initially stirred by convective flow. After solidification starts the roll cell recedes to be replaced by a chemically layered conductive melt that eventually solidifies with rather uniform eutectic structure. Upon re-melting, the morphology of the interface adopts a profile that is predetermined by the original solid structure. Those patterns, as well as the flow, are different from single element solid melting experiments and have yet to be modeled. Under high thermal gradient the convective flow mixes the binary melt and the visualized density pattern eventually becomes that of a homogeneous melt.
TL;DR: In this article, the Vickers hardness indentations on the two major habit planes (100 and (001) of the solution grown ZTS crystal have been carried out at various azimuthal orientations of the indentor, keeping other variables constant.
Abstract: The Vickers hardness indentations on the two major habit planes (100) and (001) of the solution grown ZTS crystal have been carried out at various azimuthal orientations of the indentor, keeping other variables constant. The observed anisotropic variations have been explained on the basis of effective resolved shear stress on the active slip system in the crystal. The detailed results are reported in the paper.
TL;DR: In this paper, the lattice structure of crystals checked by powder X-ray diffraction is isomorphous to YAB with space group R32, and the dependence of crystal habits and growth conditions is discussed.
Abstract: Nd 3+ , Er 3+ and Cr 3+ doped large single crystals of YAl 3 (BO 3 ) 4 were grown by spontaneous crystallisation and by top-seeded solution growth (TSSG) from a K 2 Mo 3 O 10 and B 2 O 3 flux. The crystals were grown in orientation with cooling rate 2.4°C/day. The small crystals grown by spontaneous nucleation usually had simple needle shape, while the large crystals grown by TSSG method had either isometrical habit or tabular one. The results suggest that the extremely large pinacoid faces appearing in the case of YAB:Cr 3+ growth are due to a high temperature gradient in the flux, and evaporation of the solution. The lattice structure of crystals checked by powder X-ray diffraction is isomorphous to YAB with space group R32. The dependence of crystal habits and growth conditions is discussed.
TL;DR: In this article, the effect of gamma-radiation on electrical and optical parameters was investigated using triglycine sulphate (TGS) doped with orthonitroaniline (ONA) irradiated with different doses of gamma radiation.
Abstract: Crystals of triglycine sulphate (TGS) doped with orthonitroaniline (ONA) irradiated with different doses of gamma-radiation were used to investigate gamma-radiation effect on electrical and optical parameters The absorption coefficient and the reflectance were measured and hence the extinction coefficient, the optical refractive index and the dielectric constants (er′, er″) of unirradiated and irradiated TGS crystals were calculated Values of the allowed indirect optical energy gap Egopt of TGS doped with ONA were calculated as a function of gamma-dose Value of Egopt decreases from 472 eV to 425 eV with increasing gamma-doses from 0 up to 3 Mrad The values of the static dielectric constant er(0) and the effective electrical conductivity sigma0 at room temperature and their dependence on gamma-dose were also calculated
TL;DR: In this article, the conditions necessary for order formation are analyzed for hexabenzocoronene (HBC) and naphthalene-tetracarboxylic-dianhydride (NTCDA) on graphite, MoS 2 and GeS.
Abstract: Epitaxially ordered thin films of large planar organic molecules can be obtained on layered inorganic semiconductors by organic molecular beam deposition in UHV. Analysis by low energy electron diffraction (LEED) and thermal desorption spectroscopy (TDS) yields structural parameters and binding energies. The conditions necessary for order formation are analyzed. Epitaxial data are given for hexabenzocoronene (HBC) and naphthalene-tetracarboxylic-dianhydride (NTCDA) on graphite, MoS 2 and GeS.
TL;DR: In this article, the precipitation of hydroxyapatite (HAp) in a continuous process using microwave heating and Ca/citrate/phosphate solutions is presented.
Abstract: The precipitation of hydroxyapatite (HAp) in a continuous process using microwave heating and Ca/citrate/phosphate solutions is presented. Calcium deficient HAp particles in the nanometric size range (<100 nm), with needle-like morphology, were obtained. These chemical and morphological characteristics do not change with the residence time, and are similar to those of HAp obtained in a batch process using also microwave heating and Ca/citrate/phosphate solutions. On the other hand, the steady state is reached faster than in the precipitation of HAp in a MSMPR reactor using non-complexing solutions and conventional heating. In the latter process submicronic (<1 mikrom) needle-like particles are obtained.
TL;DR: In this paper, the lattice dynamics of 12 chalcopyrite type compounds were investigated based on four different short range force constant models and a set of different solutions can be obtained which can be distinguished by their force constant patterns.
Abstract: The lattice dynamics of 12 chalcopyrite type compounds CuAlS 2 , CuGaS 2 ,CuInS 2 , AgGaS 2 , AgGaSe 2 , AgInSe 2 , ZnSiP 2 , ZnGeP 2 , CdSiP 2 , CdGeP 2 , CdSnP 2 , and CdGeAs 2 have been investigated based on 4 different short range force constant models. In all models a set of different solutions can be obtained which can be distinguished by their force constant patterns. For a comparison of the calculated force constants it is therefore necessary to use the data of the comparable minima. From the set of solutions one is selected by physical reasoning and complete results for a model with 8 force constants are given for this minimum for all 12 compounds. The calculated force constants, normal co-ordinates and potential energy distributions are compiled and discussed.
TL;DR: In this article, single crystals of lithium niobate doped with 0.03 and 0.1% of Cu or Fe ions were grown by the Czochralski technique.
Abstract: Single crystals of lithium niobate doped with 0.03 and 0.1 at.% of Cu or Fe ions were grown by the Czochralski technique. Optical absorption spectra in visible and infrared regions before and after • irradiation with doses up to 10 5 Gy were measured and positions of both dopants in LiNbO 3 lattice were analyzed according to changes in optical absorption in the range of OH group absorption. Some properties of crystals doped with Cu during the growth processes were compared to those for specimens doped by thermodiffusion. It was observed that doping with Cu results in an increase of crystal resistance to radiation.
TL;DR: In this paper, the micro-pulling-down method was used to grow transparent, transparent, and crack-free KNbO 3 crystals from the melts containing excess of K 2 O as a flux.
Abstract: The crystals of KNbO 3 have been grown by the micro-pulling-down method. Colorless, transparent, and crack-free crystals were produced from the melts containing excess of K 2 O as a flux. Growth of relatively large size (up to 2 mm in diameter and up to 30 mm in length) single crystals was found is possible using the crucibles with corresponding nozzle size (up to 2.0 mm in outer diameter). Second harmonic generation was observed in the crystals irradiated by fundamental beam with wavelength about 860 nm.
TL;DR: In this paper, the optical properties of cerium doped YAG single crystals were investigated after thermal annealing at 1400°C and 1200°C in N 2 +H 2 mixture and subsequent γ or proton irradiation.
Abstract: Changes of optical properties of cerium doped YAG single crystals (0.05, 0.1, 0.2 at. % Ce, and 0.2 at. % Ce + 0.1 at. % Mg) after thermal annealing at 1400°C in air or 1200°C in N 2 +H 2 mixture and subsequent γ or proton irradiation were investigated. For initial Ce 3+ contents 0,05 at. % a decrease of the final Ce 3+ concentration was observed. Appropriate changes in luminescence of Ce: YAG crystals were observed as a consequence of dopant concentration changes. They were small after γ-irradiation of Ce: YAG crystals with Ce 3+ content >0,05at.% and reached about 100% after γ-irradiation of crystals with Ce 3+ content <0.05 at. %.
TL;DR: In this article, the crystal growth of sodium nitrate and potassium nitrate from aqueous solutions, in a perfectly stirred batch crystallizer, has been studied considering the effect of temperature, supersaturation degree, and the size of seed crystal growth rate.
Abstract: In this paper, the crystal growth of sodium nitrate and potassium nitrate from aqueous solutions, in a perfectly stirred batch crystallizer, has been studied considering the effect of temperature, supersaturation degree, and the size of seed crystal growth rate. The mass transfer coefficients obtained correlated with Re, Sc and NL dimensionaless numbers. Supersaturation curve determination using a 0.5 mW He-Ne laser, connected to an automated data acquisition system, was the first stage of the study. The supersaturation and saturation curves were closely parallel with average DT value of 4.1 and 6.8 °C for KNO3 and NaNO3 respectively. For the growth kinetics order, unit values were found for both salts, with diffusion as a controlling stage.
TL;DR: In this paper, the lattice dynamics of 12 chalcopyrite type compounds were investigated based on a rigid ion model and the calculated force constants, normal co-ordinates and potential energy distributions were compiled and discussed.
Abstract: The lattice dynamics of 12 chalcopyrite type compounds CuAlS 2 , CuGaS 2 , CuInS 2 , AgGaS 2 , AgGaSe 2 , AgInSe 2 , ZnSiP 2 , ZnGeP 2 , CdSiP 2 , CdGeP 2 , CdSnP 2 , and CdGeAs 2 have been investigated based on a rigid ion model. As the anisotropy of the dynamic charges is not very pronounced the calculations were done assuming isotropic charges. The calculated force constants, normal co-ordinates and potential energy distributions are compiled and discussed.
TL;DR: In this paper, the magnetic field effect on diffusion experiments in vertical capillaries was relatively minor, while the damping effect of the magnetohydrodynamic damping was clearly demonstrated in horizontal and vertical capellaries.
Abstract: In liquid diffusion measurements, the main problem is the additional mass transport by convection. In the system indium-tin, convection caused by density gradients in horizontal and vertical capillaries was characterised, and the magnetohydrodynamic damping was investigated experimentally. While the magnetic field effect on diffusion experiments in vertical capillaries was relatively minor, the damping effect of the magnetic field could be clearly demonstrated in horizontal capillaries. Comparing these experiments with experiments in microgravity it can be seen that in the investigated system convection was practically completely suppressed by transversal magnetic fields higher than 3T. In electrically conducting crucibles, the sample was mixed by Lorentz forces on account of thermoelectric currents.
TL;DR: In this paper, the capacitance and dielectric constant have been measured from 303 K to 383 K in the frequency range of 10 kHz to 10 MHz, the a.c. conductivity σ is calculated at different frequencies for various temperatures.
Abstract: Thin films of Bi 3 Si 3 have been prepared by vacuum deposition technique onto well cleaned glass and freshly cleaved KBr substrates. The film thicknesses are measured by Tolansky technique. The capacitance and dielectric constant have been measured from 303 K to 383 K in the frequency range of 10 kHz to 10 MHz, The a.c. conductivity σ is calculated at different frequencies for various temperatures. The relation σ ω 1 fits well and the value of n is found to be greater than 1.5 and above at high frequencies suggests that the conduction mechanism in Bi 2 Se 3 thin fil is hopping. The d.c. conduction studies revealed the non-ohmic type of conduction Log 1 versus Log V plot). From the Log 1 versus F 2 plot, the field lowering coefficient β is evaluated.
TL;DR: In this paper, the informational content of Kossel interferences excited by electron and synchrotron radiation beams selected examples of microstructural applications, such as the precision determination of lattice constants, the precision determinations of crystallographic orientation of single grains, the determination of local stresses/strains and tetragonal distortions of cubic lattices including the description of a variety of methods for analysis are presented.
Abstract: Starting from the origin and the informational content of Kossel interferences excited by electron and synchrotron radiation beams selected examples of microstructural applications, such as the precision determination of lattice constants, the precision determination of crystallographic orientation of single grains, the determination of local stresses/strains and the determination of tetragonal distortions of cubic lattices including the description of a variety of methods for analysis are presented.
TL;DR: In this article, the authors present a review of the present status of high pressure solution growth of GaN single crystals and their characterization, including the thermodynamic properties of the system, the kinetic description of the growth which include the N, dissolution, the volume transport and the surface kineties.
Abstract: The present paper reviews presentation of the present status of high pressure solution growth of GaN single crystals and their characterization. The main aspects of the growth include: the thermodynamic properties of the system, the kinetic description of the growth which include the N, dissolution, the volume transport and the surface kineties. The important properties of GaN crystals derived from optical, X-ray, electron transport and positron annihilation measurements are presented. Also etching properties and their relation to the growth morphology and doping are discussed.
TL;DR: In this paper, the influence of magnetic field on some kinetic crystallization parameters of the systems zinc sulfate - water and copper sulfate- water were investigated in a series of controlled batch cooling experiments.
Abstract: The influence of the magnetic field on some kinetic crystallization parameters of the systems zinc sulfate - water and copper sulfate - water were investigated in a series of controlled batch cooling experiments. The solutions were exposed to magnetic fields with different intensities, up to a maximum of 0.7T. A clear influence of magnetic field on the zinc sulfate crystallization parameters was found: an increase in the saturation temperature, a decrease in the metastable zone width, and increased growth rate and average crystal size. These effects were observed for the diamagnetic zinc sulfate, but not in similar experiments with paramagnetic copper sulfate.
TL;DR: Yttrium-aluminum garnets, strontium and barium lanthanum gallates, lithium niobate and tantalate as-grown crystals and doped by diffusion with rare-earth (Nd, Dy, Er, Tm, Ho, Pr, Ce) and metal transition elements (Mn, Cr) were investigated optically and using Electron Spin Resonance method before and after gamma, electron and proton irradiation as discussed by the authors.
Abstract: Yttrium-aluminum garnets, strontium and barium lanthanum gallates, lithium niobate and tantalate as-grown crystals and doped by diffusion with rare-earth (Nd, Dy, Er, Tm, Ho, Pr, Ce) and metal transition elements (Mn, Cr) were investigated optically and using Electron Spin Resonance method before and after gamma, electron and proton irradiation.