Crystal growth and dislocation structure of gallium antimonide

Single crystals of GaSb have been grown by the Czochralski method under reducing conditions. Crystals were grown in the 〈100〉, 〈111〉, and 〈112〉 directions. The 〈111〉 growth direction was found to be the most suitable for the successful and reliable crystal growth. Dislocation densities in 〈111〉 oriented crystals were examined by chemical etching. The etch pits density in these crystals didn't exceed the value of 1 × 10² cm⁻².     

Cuprous oxide microcrystals via hydrothermal approach: morphology evolution and photocatalytic properties

Cuprous oxide (Cu₂O) microcrystals with various morphologies were prepared under mild hydrothermal condition. The samples were characterized by means of XRD, SEM, and UV/DRS. The morphology of the as‐prepared Cu₂O microcrystals typically had cubic symmetry and the morphology evolution from radial, six hollow branches to truncated octahedra (again cubic) were realized by adding acetic acid. The peak relative intensity of XRD pattern shows that the exposed planes of samples is consistent with their morphology. A possible growth mechanism of Cu₂O microcrystals is also proposed. The behavior of adsorption and photocatalysis of Cu₂O microcrystals was investigated by degrading methyl orange (MO) in aqueous solution. The results show that the as‐prepared Cu₂O radial six hollow branches microcrystals with exposed {110} planes have higher degradation efficiency to methyl orange (MO) than cubic ones with exposed {100} planes and truncated octahedral with exposed {111} planes microcrystals.     

Synthesis,transformation to octahedron‐like crystals,and gas‐sensing property of six‐horned nanospheres of Cu2O

Single‐crystal six‐horned nanospheres of Cu₂O with a diameter of 760 nm in average were prepared in aqueous solution of CuCl₂and NaOH by using ascorbic acid as the reductant in the presence of sodium dodecyl benzenesulfonate (SDBS) at room temperature. The horn grows along the <100> direction, which is consistent with the protuberant direction of an apex of octahedron. The formation process of six‐horned nanospheres included two steps: the formation of Cu₂O nanospheres via Ostwald ripening process, and the appearance of horns on the surface of nanospheres under low concentration of SDBS. As increasing the concentration of SDBS, the six‐horned nanospheres could be transformed into octahedron‐like Cu₂O. And at the same concentration of SDBS, keeping the volume ratio of water and ethanol in mixed solutions as 1:1, Cu₂O octahedra were obtained. Moreover, gas‐sensing property showed that six‐horned nanospheres of Cu₂O had higher sensitivity compared with Cu₂O nanospheres and Cu₂O octahedra to ethanol gas (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Large-size and high-quality Zn2TiO4 single crystal grown by the optical floating zone method

Crack-free and transparent Zn₂TiO₄ single crystals of 4–6 mm in diameter and 30 mm in length have been grown by the optical floating zone method. The powder X-ray diffraction (XRD) results show that the as-grown crystals have the spinel-type Zn₂TiO₄ structure. XRD² measurements on Zn₂TiO₄ wafers cut perpendicular to the growth direction display only one peak at 42.7°, which indicates that the Zn₂TiO₄ single crystals grow along the 〈4 0 0〉 direction (a-axis). The formation of bubble inclusions was effectively suppressed by lowering rotation rate. Transmission polarized-light microscopy results showed that as-grown crystals were free of low angle grain boundaries.     

Radial and axial impurity distribution in high-purity germanium crystals

To grow high purity germanium (HPGe) crystals in an underground environment for ultra-low background experiments is being studied. In the present work, HPGe crystals along 〈100〉 direction have been grown by the Czochralski method. In order to investigate the distribution of the impurities as a function of length for a grown crystal, i.e. the axial direction, we fabricated a system to measure the resistivity along the axial direction at both room temperature and liquid nitrogen temperature. The distribution of the impurities along the radial direction was measured with a Hall Effect System. The results show that the carrier concentration in some crystals grown in a hydrogen atmosphere has an impurity level of about 10¹⁰/cm³, which meets the requirements of detector-grade crystals.     

Plastic Deformation of Cesium Iodide Single Crystals at High Temperatures

The plastic deformation of CsI crystals of three crystallographic orientations 〈100〉. 〈110〉. and 〈111〉 at temperatures from 423 to 773 K (0.5 to 0.86T_m) and strain rates from 2 × 10⁻³ to 10⁻⁵ s⁻¹ is studied. Four-stage stres-strain curves were found, three stages being more and more distinct with an increase in temperature up to 623 K above which stage III prevails. For all the temperatures, strain rates and oreintations studied the superplasticity features (jerky flow, deformation localization, active dynamical recovery etc.) were observed. The thermal activatoin analysis has shown that the rate of high temperature deformation of CsI is controlled by dislocation climb limited in its turn by mobility of cation vacancies (quasiviscous creep).     

Microstructures on {111} faces of stannic iodide single crystals

Single crystals of stannic iodide (SnI₄) havebeen grown using the controlled reaction between SnCl₂ and KI by diffusion process in silica gel medium. Orange to reddish octahedral stannic iodide crystals up to 3–4 mm in size have been grown at room temperature. Optical studies have been made on the various surface structures of {111} faces of the asgrown crystals. On octahedral faces of these crystals, triangular-shaped hillocks with growth layers in the 〈110〉 directions have been observed. Occasionally, growth spirals on octahedral faces have also been reported. Close loops of growth fronts have been investigated and have been interpreted. It has been suggested that two-diemensional nucleation, spreading and pilling up of triangular growth layers is mainly responsible for the growth and occasionally the growth is due to screw dislocations. The implications are discussed.     

Change in the crystal structure of zink(II) sulphate heptahydrate and magnesium(II) sulphate heptahydrate due to isodimorphous substitution by copper(II), iron(II), and cobalt(II) ions

The physico-chemical analytical data on the systems ZnSO₄(MgSO₄)–CuSO₄(FeSO₄, CoSO₄ resp.)–H₂O at 25.0°C have shown that due to isodimorphous substitution of Zn²⁺, Mg²⁺ resp., in the orthorhombic crystals of ZnSO₄ · 7 H₂O MgSO₄ · 7 H₂O, resp. for Cu²⁺, Fe²⁺ or Co²⁺ above a specific degree of ionic substitution, the orthorhombic crystals are converted into monoclinic mixed crystals. The crystal phases are characterized by X-ray diffraction, microscopic and optical studies. The dominant effect of the admixed Cu²⁺, Fe²⁺, Co²⁺ ions is explained in terms of their electronic configurations, for which, owing to the operation of the Jahn-Teller effect, a deformation of the regular octahedral arrangement of the water ligands about the metal ion is found to occur. The strongest deforming effect is that of Cu²⁺ ions followed by the Fe²⁺ ions, the weakest deforming effect being that of Co²⁺ ions.     

TEM-Untersuchungen von Gitterfehlern in ZnSiP2-Einkristallen

Results are dealt with concerning TEM investigations of lattice defects in ZnSiP₂ single crystals. After the crystal growth dislocations or stacking faults were found in a few cases only. More frequently twins were present in the microstructure. The crystallographic elements of twinning are {112} 〈111〉. After plastic deformation by bending at 900 °C local dislocation arrangements with high defect density (N_v ≈ 10⁶…︁ 10⁷ cm⁻²) were observed. By means of the diffraction contrast one Burgers vector b = 1/2 〈111〉 could be identified. In some cases the crystals also contained wide deformation stacking faults, which were limited by partial dislocations. The density of twins was not increased under the conditions of deformation reported here. As it can be concluded from investigations of Oettel et al. and from the results of the twin analysis, slip and generation of stacking faults take place on {112}-planes in ZnSiP₂ crystals. Crystallographic considerations on both processes are dealt with.     

Burgers Vectors of Dislocations in Creep-deformed Fe3Si Single Crystals

In creep-deformed Fe₃Si single crystals the Burgers vectors of the dislocations were examined by transmission electron microscopy. The Burgers vector in a sample deformed under conditions of 60 MPa and 575–600 °C was of the type 1/2 〈110〉, whereas 〈111〉 superlattice dislocations were not found. 1/2 〈110〉 is the shortest translation distance in the D0₃ superlattice structure of Fe₃Si.     

Preferred Growth Direction of Ni Single Crystals by the Floating-Zone Method

In Ni single crystals grown by the floating-zone method, it was found that their growth directions tended to concentrate towards the 〈111〉 or the 〈100〉 direction. An interpretation was put forward for the preferred direction of these crystals in terms of thermal stability of the crystallographic planes in the solid-liquid interface.     

Blocky and spheroidal growth in Y1.5Ba2Cu3Ox system

Solidification of Y_1.5Ba₂Cu₃O_x system was studied with the aim to find the temperature of self-nucleation. The microstructure after cooling from isothermal dwells in the temperature range 984–995 °C was analysed. It is shown that blocky YBa₂Cu₃O_7?δ crystals were self-nucleated and grown during isothermal dwells below 988 °C and spheroidal multicrystals were formed during cooling from isothermal dwells at higher temperatures. The symmetrical and radial YBa₂Cu₃O_7?δ crystal branches of spheroids grow in the 〈110〉 crystal direction.     

Morphology and orientation relations of BaCl2 precipitates in NaCl single crystals

In the present paper morphology and orientation relations of BaCl₂ precipitates in NaCl single crystals are described. It is shown that BaCl₂ precipitates of large dimensions are formed at the dislocations of a/2〈110〉{100}, the dislocation lines of which are oriented in the directions 〈210〉.     

Indicators of the magnetic state in the charge distributions of MnO, CoO, and NiO. II: Para-and antiferromagnetism of CoO

X-ray diffraction intensities from CoO were measured above and below the Néel temperature. The data were submitted to a non-parametric multipole analysis aiming at formulation of experimentally valid statements on the nature of the charge distribution. Strong “bonding maxima” are seen between the Co 〈110〉O nearest neighbors. In the paramagnetic state they are formed by the Co-ion alone, in the antiferromagnetic state they involve a strong CoO coupling. The outer electrons of oxygen give rise to slight maxima in the 〈110〉 directions, making the atom into an O^2? ion. In the paramagnetic state, their coupling with the bonding feature forms an octahedral electron cage around each oxygen atom. Broad density maxima between the atoms in 〈111〉 directions are present in both states. They connect the “bonding maxima” in the 〈110〉 directions, more strongly in the antiferromagnetic state, building up an interatomic three-dimensional network. Such electron network structures seem to be characteristic of metal oxides more generally.     

Über die röntgenographische Analyse der mittleren quadratischen Atomverschiebungen in einigen Halbleiterkristallen

X-ray measurements of the Debye-Waller factor were performed with single crystals of Ge and of semiconducting compounds A^IIIB^V, A^IIB^VI, A^IVB^VI in the temperature range 100 K — 1000 K. From the results the mean square atomic displacements 〈u²〉 and the Debye characteristic temperatures θ of the materials were calculated. Both parameters are discussed with respect to the influence of the temperature, the influence of point defects and, in the case of the compounds, deviations from the stoichiometric composition on the thermal lattice vibrations. Finally, considerations are presented, concerning the relationship between the parameters 〈u²〉 and θ_M, respectively, and the activation energies of vacancy formation and diffusion in the materials.     

General orientational characteristics of heteroepitaxial layers of AIIBVI semiconductors on sapphire and semiconductor substrates with diamond and sphalerite structures (AIIIBV)

X-ray reflection and transmission diffractometric studies of nonisostructural heteroepitaxy showed that the spatial rotation of the crystal lattice of the grown heteroepitaxial layer with respect to the substrate lattice about the crystallographic direction common for both lattices is the most general characteristic feature of their mutual crystallographic orientation. This feature leads to the coincidence of the 〈0001〉 polar axis of the heteroepitaxial layer of the A^IIB^VI compounds with one of the 〈111〉 polar axes of the cubic substrate. The 30° and 90° rotations in the plane of heteroepitaxy and the vernier-type conjugating of the planar nets of the heteroepitaxial layer and the substrate are the particular cases of their mutual crystallographic orientations.     

Microhardness studies on as‐grown (111) faces of some alkaline earth nitrates

Single crystals of Sr(NO₃)₂, Ba(NO₃)₂ and Pb(NO₃)₂ are grown from their aqueous solutions at a constant temperature of 35 °C by slow evaporation technique. Crystals of size 8 to 10 mm along one edge are obtained in a period of 10 days. Chemical etching technique has been employed to study the dislocations in these crystals. The dislocations are randomly distributed and the dislocation density is about 10⁴ to 10⁵ /cm². Microhardness studies are made on as–grown (111) faces of these crystals upto a load of 100 g. The hardness of the crystals increases with an increase in load and thereafter it becomes independent of the applied load. These results are discussed on the basis of reverse indentation size effect. Meyer index number n for these crystals is estimated at both low and high load regions. An analysis of hardness data of these crystals as well as some other cubic crystals like alums and alkali halates are discussed using Gilman–Chin parameter H_v/C₄₄, where H_v is the microhardness and C₄₄ is the shear constant. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Long-Term Changes in Mechanical and Electrical Characteristics of CdTe Crystals after Their Exposure to a Weak Pulsed Magnetic Field

Long-term changes in mechanical and electrical properties of p-type CdTe single crystals have been revealed after their exposure to a weak pulsed magnetic field (B = 1 T, ν = 12 Hz, t_exp = 10 min). A nonmonotonic increase in the hardness of crystals (presence of two peaks) and a nonmonotonic decrease in their specific dark conductivity (three peaks) have been observed. The peaks of changes in mechanical and electrical properties correlate on the time scale. It is shown that the intensity of observed effects depends on the crystal orientation with respect to the direction of magnetic induction vector B. In particular, the observed changes in properties for B || 〈111〉 are twice as large as those for B || 〈110〉. Possible mechanisms of the observed effect are discussed.     

Growth and dissolution of BaFCl crystals

Single crystals of BaFCl have been growth by flux technique using BaF₂ and BaCl₂. Etching with formic acid revealed dislocation etch pits on (001) cleavage faces of the crystals, at room temperature. The influence of etching parameters such as undersaturation, temperature and concentration of poison in the etchant is studied. Decreasing the undersaturation of formic acid by reducing the percentage of water and increasing the temperature of the etchant were found not to have any effect on the morphology of etch pits. However, as the CdCl₂ poison concentration is gradually increased, the orientation of the pits change from 〈100〉 to 〈110〉 at high concentration.     

Abscheidung von Cu2O aus der Gasphase im strömenden Medium

CVD-experiments in the system Cu O H Cl N result in the growth of Cu₂O single crystals. The characteristic faces of the various forms are the {100} ones. A thermodynamic analysis permits to predict such conditions under which Cu₂O is deposited without deposition of any other phases.