Effect of Impurity Concentration and Plastic Deformation on Dislocation Density of KCl Crystals

Using the etch pit technique both the distribution and density of dislocations in undeformed and dynamically deformed nominally pure and Sr²⁺ or Pb²⁺ doped KCl crystals are examined. Additionally, the role of specimen geometry in the plastic deformation within the I deformation stage is determined. For all the crystals examined the relationship between screw dislocation density and plastic flow stress obeys the formula τ ⋍ ϱ_sc.^1/2.     

Growth parameters for large diameter float zone silicon crystals

Factors that directly affect the ability to grow dislocation free float zone silicon crystals up to 80 mm in diameter have been experimentally determined. The highest yield is obtained for 80 mm diameter crystals by starting with 68 mm to 74 mm diameter poly crystal rod stock. Lower transport speeds for crystal growth of (111) orientation crystals were 3 to 4 mm/min and for (100), 2 to 3 mm/min. Rotation rates of both upper and lower shafts were found to have an effect on growth at the solid-liquid interface. Rates established for lower shaft were 6 to 8 rpm for the (111) crystals and 3 to 4 rpm for (100), counter-clock-wise. Upper rotation rates were 2 rpm on (111) crystals and 3 to 5 rpm on (100), clockwise. Seed orientation, which is critical, was held to within plus or minus $\text{1}\text{2}\text{°}$ of perfect orientation. The minimum seed growth length was 50 to 70 mm. To assist in reducing the side lobes on (111) dislocation free crystals, a cooling ring with a flow or argon was used. For best (100) growth the shape of the lower side of a one turn copper rf work coil was made conical. Six to ten dislocation free crystals in each orientation group were produced using these parameters.     

Analysis of X‐ray extinction in crystals with inhomogeniously distributed dislocations

The secondary extinction theory of Zachariasen for mosaic crystals as well as the formalism of Becker&Coppens have been used for substructure analysis (lattice disorientations, block size, density of excess dislocations, etc.) in crystals with inhomogeniously distributed dislocations in the Bragg case of diffraction geometry. In the case of large crystals D_S ≫ Λ_hkl the mean total density ρ_D of randomly distributed dislocations was also estimated taking into account additionally the primary X‐ ray extinction treatment. In this connection two cases are considered: I) pure secondary extinction related to arrangement of dislocation walls and II) mixed extinction in crystals with large subgrains related to randomly distributed dislocations and arrangement of dislocation walls. In order to check the considerations, the experimental and calculated data were compared for Be (model I) and Cu (model II) single crystals. The weakly distorted single crystals of Be and Cu were experimentally investigated in the Bragg case of diffraction geometry using Cu Kα₁ radiation by means of double crystal diffractometer. A new experimental procedure was proposed. Using alternative technique for substructure analysis (for instance EBSD) the reliability of analysis based on extinction phenomenon in weakly distorted single crystals has been checked. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of doping of Ca and Ba on the dislocation distribution in melt grown KCl crystals

The effects of doping of Ca and Ba (∼ 0.02 at %) upon the dislocation distribution in melt grown KCl crystals without cellular segregation were studied by an etch pit method in connection with the dispersion state of the dopants, which was examined by the dark field illumination. – (1) In the Ca-doped crystal, in which the dopants were distributed uniformly, the formation of subboundaries was completely suppressed and dislocations were distributed at random. (2) In the Ba-doped crystal, however, the dopants were non-uniformly distributed and the dislocations tended to form subboundaries. The dislocations within the subgrains were distributed in a non-uniform manner. (3) The dislocation density in the Ba doped crystal was higher than that of undoped or Ca-doped crystal. This was explained by the mechanism similar to the Tiller's prediction. – Finally, the stress distribution due to the concentration fluctuation was examined by the birefringence patterns.     

Facet Formation in Garnet Crystals

Formation of {110} and {211} type facets in rare-earth aluminium garnet crystals grown along different crystallographic directions is analyzed and it is shown that D/2R parameter (where D is the crystal diameter and R is the curvature radius of spherical growth interface) may be used to characterize the number of originating facets and their configuration in crystals.     

Dislocation densities in copper single crystals after thermal treatment

Copper crystals of high purity and doped with nickel were subjected to a long time thermal treatment at 1050°C, in order to reduce the as-grown dislocation density of about 10⁷ cm⁻². A dissolution of the dislocations during their motion to the crystal surface was observed. Regions of different dislocation densities arose. Finally the crystals exhibited constant dislocation densities of 10² cm⁻². Such a perfection or a better one of the crystals is reached only by a long time treatment, since the dislocation velocity without external stresses cannot exceed 1 · 10⁻⁷ cm · s⁻¹ in copper single crystals of high purity.     

Plastic bend in a growing crystal

In case of nonlinear axial temperature distribution the relaxation of thermoelastic stresses results in the plastic bend of the growing crystal, i. e. in the generation of a residual lattice curvature equal to ϱ b . Based on results from Billig and from Indenbom the author presents estimations of dislocation densities (ϱ) (i. e. residual lattice curvature) taking into account an elastic limit differing from zero. It is shown that sign and value of the residual lattice curvature may be effectively used as criteria pointing out how thermal conditions should be changed for abtaining more perfect crystals. This approach application allowed to grow larger KCl single crystals (300 mm in diameter more than 100 kg by weight) with better structure perfection (specific subboundaries surface 2—3 cm²/cm³, mean subgrain dimension 0.6—1 cm, mean mutual disorientation of subgrains of not more than 6′).     

掺Sr2+溴化铈晶体的生长与闪烁性能研究

采用坩埚下降法生长了直径为25.4 mm的纯溴化铈晶体和0.1%、0.2%和0.5%(摩尔分数)Sr²⁺掺杂的溴化铈晶体。将所生长晶体加工成直径25.4 mm、厚度10 mm的坯件,并进行紫外和X射线激发荧光光谱、¹³⁷Cs源激发多道能谱等测试。结果表明:Sr²⁺掺杂会导致晶体X射线激发下的发射光谱出现轻微红移,而随着Sr²⁺掺杂量的增加,晶体的能量分辨率依次提高,光输出依次降低;当Sr²⁺掺杂量为0.5%时,溴化铈晶体的能量分辨率最高,达3.83%@662 keV,但过高含量的Sr²⁺掺杂会造成晶体生长困难。综合考虑晶体性能和生长情况,Sr²⁺掺杂量为0.2%时较为适宜,所获得的ϕ25.4 mm×25.4 mm CeBr₃∶0.2%Sr晶体封装件的能量分辨率为3.92%@662 keV。     

The influence of metallic substitution on the physical properties of manganese mercury thiyocyanate crystals

Good optical grade single crystals of pure, Cd²⁺ and Mg²⁺ doped Manganese Mercury Thiyocyanate (MMTC) crystals are grown by slow solvent evaporation technique at room temperature. Single crystal XRD studies reveal that the incorporation of metallic dopants has not changed the structure of the parent crystal. The SHG efficiencies of the pure and doped samples of MMTC are measured by Kurtz Perry powder method and the results are compared with urea. It is evident from microhardness study that the presence of dopants has increased the mechanical strength of MMTC crystal. The TG/DTG studies confirm that the thermal decomposition temperatures of pure (353°C), Mg²⁺ doped (363°C) and Cd²⁺ doped (365°C) MMTC are relatively high when compared to other NLO crystals of the same family. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Finite element analysis of dislocation density during bulk single crystal growth (effect of doping atoms in InP single crystal)

A computer code for simulation of dislocation density in a bulk single crystal during liquid encapsulated Czochralski (LEC) or Czochralski (CZ) growth process. In this computer code, the shape of crystal–melt interface and the temperature in a crystal at an arbitrary time were determined by linear interpolation of the results that were discretely obtained by heat conduction analysis of a CZ single crystal growth system. A dislocation kinetics model called Haasen–Sumino model was used as a constitutive equation. In this model, creep strain rate is related to dislocation density, and this model extended to multiaxial stress state was incorporated into a finite element elastic creep analysis program for axisymmetric bodies. Dislocation density simulations were performed using this computer code for InP bulk single crystals with about 8″ in diameter. In the analysis, the effect of dopant atoms on the dislocation density was examined. In the case of a low doped InP single crystal, dislocations are distributed in the whole of the crystal. On the other hand, in the case of a highly doped InP single crystal, dislocations are localized at both the central and peripheral regions of the crystal.     

Electrical Conductivity and Crystal Structure of Pure and SrCO3-doped K2CO3

Electrical conductivity of pure and SrCO₃ doped potassium carbonate has been investigated in the temperature range between 350 and 800 °C. Sintered carbonate mixtures were analysed by X-ray powder diffraction techniques at room temperatures. The conductivity of SrCO₃ doped K₂CO₃ increases nearly linear up to 10 mol.% and decreases in the range between 20 and 50 mol.% continously. X-ray diffraction patterns do not show changes up to 10 mol.% SrCO₃ in the host lattice. The compound K₂Sr(CO₃)₂ was found for samples containing 15–50 mol.% SrCO₃. The lattice constants of hexagonal crystals which are isotypic with K₂Ca(CO₃)₂ are a₀ = (534 ± 1) pm and c₀ = (1352 ± 2) pm.     

An Investigation on the Lattice Distortion in Urea and KCl Doped KDP Single Crystals by X‐ray Diffraction Studies

Potassium dihydrogen phosphate (KDP) doped with different mole concentrations of Urea and KCl were grown using low temperature solution growth technique. X‐ray diffraction studies were carried out on the grown crystals using a Shimadzu X‐ray diffractometer with CuKD radiation. X‐ray study revealed that the structures of the doped crystals are slightly distorted compared to the pure KDP crystal. This may be attributed to strains on the lattice by the adsorption of urea and KCl.     

Optical defects in barium—strontium niobate single crystals

The distributions of edge dislocations and residual mechanical stresses in Ba_xSr_1-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.     

Growth and Characterization of Na2CaGe6O14 Single Crystals

Transparent, crack-free Na₂CaGe₆O₁₄ (NCG) single crystals were successfully grown using the Czcchralski technique. The largest crystal had 30 mm in total length and 18 mm in maximal diameter. Best crystal quality was achieved under low temperature gradient arrangement. The crystal structure of NCG has been refined from single crystal X-ray diffraction data. Some piezoelectric properties of NCG are reported.     

Change in dislocation distribution of KCl single crystals during thermal cyclic annealing

The change in dislocation distribution of KCl single crystals during thermal cyclic annealing was studied by etch pit method. The results obtained are summarized as follows. (1) In contrast to the case in Cu (KITAJIMA et al.; HASEGAWA et al.), the dislocation distribution in KCl crystals became non-uniform with an increase in the cyclic annealing time, i.e., in the region near the surface, many sub-boundaries were formed, but in the interior, the density of dislocations and sub-boundaries decreased. The cyclic annealing is more effective in reducing the dislocation density than the isothermal annealing. (2) The longer the period of thermal cycle, the more effective in reducing the dislocation density. (3) The larger the temperature difference between the maximum and minimum during one cycle, the more effective in reducing the dislocation density. (4) In the Sr-doped crystals, the thermal cyclic annealing was also effective in reducing the dislocation density within subgrains but sub-boundary length per unit area slightly increased by the cyclic annealing. (5) When the samples were annealed under the atmosphere of Cl₂, the dislocation density remarkably increased against our expectation, although the scattering centres had disappeared by this treatment.     

Polycrystalline Synthesis and Single Crystal Growth of AgGaS2

A modified two temperature vapor transport procedure has been used to synthesize AgGaS₂ polycrystalline materials at 1060 °C from high-purity Ag, Ga, S elements. The results showed that the polycrystalline materials are pure single phase AgGaS₂ by X-ray powder diffraction analysis. The polycrystalline ingot includes a few interior voids and has a high mass density. The AgGaS₂ ingot with 12 mm in diameter and 20 mm in length has been grown by the modified Bridgman technique in two-zone vertical furnace. As-grown AgGaS₂ ingot was characterized by the X-ray diffraction technique, obtained the rocking curve of the crystal (011) face, it is shown that the ingot is AgGaS₂ single crystal. The infrared transparent of the crystal at 2 ∼ 10μm is 49% (and absorption coefficient is 0.74 cm^—1).     

Dislocations and dislocation reduction in space grown GaSb

The behaviour of dislocations in GaSb crystals grown in space both from a stoichiometric melt (floating zone method, FZ) and a Bi solution (floating solution zone, FSZ) respectively, is studied. Predominantly straight 60° dislocations with Burgers vectors of the type b = a/2 <110> in (111) glide planes are identified. In the 20 mm long FZ single crystal the linear growing out of the dislocations is observed which reduces the dislocation density in the centre of the crystal to values below 300 cm^–2. The Bi incorporation in the FSZ crystal results in a misfit between seed and grown crystal and in a network of misfit dislocations at the interface. Thermocapillary convection during growth as well as the surface tension may be the reasons for the presence of curved dislocations and the higher dislocation density within a 1 – 2 mm border region at the edges of both of the crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure sensitivity of relaxation phenomena in NaCl and KCl crystals doped with some divalent impurities (II) effect of plastic deformation

By studying: 1/the role of dislocations in the origin of the C-ITC-peak in undeformed crystals, 2/ the effect of plastic deformation upon the behaviour of this peak, and 3/ the recovery of the deformation-induced changes of the basic characteristics of this peak (H^C, T_M^C) it has been confirmed that dislocation lines surrounded by the Cottrell-like atmospheres can be considered as polarizable entities related with the high-temperature dielectrical response of as cleaved NaCl and KCl crystals doped with divalent impurities. The Maxwell/Wagner model of polarization effects in heterogeneous dielectrics satisfactory accounts for the majority of the experimental data. The quantitative analysis of the results obtained yields some additional informations concerning the interaction- and motion-parameters of the defects considered.     

Luminescence characteristics of undoped and Eu‐doped GdCa4O(BO3)3 single crystals and nanopowders

Single crystals of GdCa₄O(BO₃)₃ (GdCOB) pure and doped with Eu concentration of 1 and 4 at% were grown by the Czochralski and micropulling‐down methods. The distribution of Eu ions in GdCOB crystals was uniform. The substitutions of Eu³⁺ in Gd, Ca(1) and Ca(2) cation sites and eventually formation Eu²⁺ have been investigated. The spectroscopic properties of crystals are compared with the properties of nanopowders obtained by sol‐gel method. Radioluminescence spectra of undoped GdCOB crystal show the characteristic emission of Gd³⁺ at about 312 nm, whereas this emission dramatically decreases in Eu‐doped crystals upon X‐ray excitation, as well as in Eu‐doped nanopowders excited in vacuum ultraviolet (VUV) region. The VUV excitation in the range 125‐333 nm for Eu‐doped samples leads to strong emission in red coming from the ⁵D₀ multiplet of Eu³⁺, only. In the photoluminescence decay kinetics of 312 nm emissions substantial shortening and departure for single exponential decay in Eu‐doped samples is clearly observed. Higher Eu doping results in further acceleration of the decay. In undoped GdCOB crystal, the lifetime of the Gd^{3+ 6}P_7/2 multiplet is 2.79 ms. The Eu^{3+ 5}D₀ decay kinetics monitored at 613 nm are rather constant. Numerical fitting of fully exponential curves, reveals lifetimes 2.7 ms for nanopowder and 2.5 ms for single crystal. The results suggest that this material may be used as a red phosphor in plasma display panels in nanopowder form because of strong excitation band of Eu³⁺ luminescence in the 160‐200 nm regions. Contrary to nanopowder sample, such an excitation band, attributed to the Gd³⁺–O^2– charge transfer was not observed in crystal obtained by the micropulling‐down method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,growth and characterization of single crystals of pure and thiourea doped L‐glutamic acid hydrochloride

L(+)Glutamic acid hydrochloride [HOOC (CH₂)₂CH(NH₂) COOH·HCl], a monoamino dicarboxylic acid salt of L‐Glutamic acid was synthesized and the synthesis was confirmed by FTIR analysis. Solubility of the material in water was determined. Pure and Thiourea doped L‐Glutamic acid hydrochloride crystals were grown by low temperature solution growth using solvent evaporation technique. XRD, UV‐Vis‐NIR analyses were carried out for both pure and thiourea doped crystals. The crystals were qualitatively analyzed by EDAX analysis and the presence of thiourea was confirmed. The cell parameters of L‐Glutamic acid hydrochloride have been determined as a = 5.151 Å, b = 11.79 Å, c = 13.35 Å by X‐ray diffraction analysis and it crystallizes in orthorhombic space group P2₁2₁2₁. UV‐Vis‐NIR spectra analysis showed good optical transmission in the entire visible region for both pure and doped crystals. Micro hardness of both pure and doped crystals has been determined using Vickers micro hardness tester. The SHG efficiencies of both pure and doped crystals were determined using Kurtz powder test and pure L‐Glutamic acid hydrochloride crystal was found to possess better efficiency than thiourea doped L‐Glutamic acid hydrochloride crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)