The Morphology of Hydrothermally Grown Plagioclase

Plagioclase crystals Ab₂₀An₀₀ and nearly pure anorthite were grown on the surface of artificial melts by hydrothermal treatment at 2 kb. The average crystal size was 0.002 to 0.008 mm. In the temperature range of 400° to 600°C a pseudohexagonal habit was observed for anorthite while a lath-like habit due to the prevalence of {010} was found for the Ab₂₀An₈₀ composition. Dominating faces are {010} {130} {110} {100} {110} {130} in the zone [001] and {021} {111} {111} {021} {111} {111} together with {001}.     

Zum chemischen Transport der Übergangsmetalldioxide mit Tellurhalogeniden

The thermodynamic relationship between the transition metal dioxides and their tetrahalogenides is demonstrated, and a comprehensive survey on the thermodynamic values of the compounds is given. – All dioxides of the transition metals existing to 1000°C in the solid state are transportable by TeCl₄. Only those dioxides are transported by TeBr₄ which have corresponding oxide-bromides existing in the gaseous phase. – The forms of crystallographic growth are very similar. The favoured growth direction is [001], the crystal faces are {110}- and {100}-prisms, {101}- and {111}-pyramids, respectively.     

Single crystal synthesis and properties of lithium-gallium-, lithium-aluminium-oxide and mixed compounds (I) growing of LiGaO2-, LiAlO2- and LiAlxGa1−x crystals from fluxes

LiGaO₂ forms a single eutectic with PbO/B₂O₃ (molar ratio 9:4). A nearly linear slope of the liquidus curve is followed by a steep rise of the temperature coefficient of solubility. The solvent power at 1300°C is 0.35 g LiGaO₂/g PbO, B₂O₃; from 1000 to 1300°C there exist only poor differences in solubility of LiGaO₂ and LiAlO₂ in PbO/B₂O₃. LiGaO₂ crystals up to 1 p in weight grew spontaneously by slow cooling from fluxes or by evaporation of the solvent, those of about 1–1.5 p from seeds by cooling stirred fluxes. LiAlO₂ crystals are essentially smaller (6 mm). – By partial substitution of Ga₂O₃ by Al₂O₃ mixed crystals LiAl_xGa_1−xO₂ result. In the case of x ≦ 0.5 the coefficient of segregation remains ≦1. The al concentrations along the polar axis decrease by more than 25 p.c., perpendicular to [001] they keep constant till to the crystal surface. – Crystals show hypermorphism from mm2 to mmm. With high initial exceedings only {110} and {011}, with lower ones also {120}, {130}, {210} and {310} as well as the reduced {100}, {010} combinations are observed. – LiGaO₂ crystals grow by nucleous, sceletal or faceted growth resp. during the cooling period. – Primarily at 1270°C formed nuclei up to 1150°C grow to critical dimensions (≈0.5 mm) and develop to the main branch along [001]. Primary branches deflect to [010]. The convex secondary branches intergrow along (110), often including flux. With decreasing temperature a new crystallisation front is formed at the periphery leading to a stable faceted growth at about 1000°C.     

Dislocations in magnetic garnet crystals

1. Dislocations in magnetic flux-grown garnet crystals (Y₃Fe₅O₁₂ and others) have been observed. As a rule, {110} growth pyramids have more defects than {211} ones. 2. The highest content of defects (dislocation density 10³–10⁴ cm⁻²) is observed in Y₃Fe₅O₁₂ that grows on crucible walls adjacent to the free surface of the solution where the flow of heat is not uniform to the greatest degree. Bottom grown crystals usually have less dislocations. Far fewer dislocations are in wall grown crystals, least of all dislocations are contained in crystals that grow inside the solution. The solution pouring off at the end of the crystallization period increases dislocation density by some dozens. 3. Heat treatment decreases dislocation density. The less dislocation content and the lower ordering are in the initial crystal, the higher heat treatment effectiveness.     

Effect of flux composition on the morphology of KTiOPO<Subscript>4</Subscript> crystals

KTiOPO₄ crystals have been grown from flux of K₆P₄O₁₃ in the presence of K₂SO₄, Li₂SO₄, and Na₂SO₄ salts and V, Cr, Ni, Co, Cu, Mo, Ba, Ce, Er, and W impurities. The crystals grown are characterized by well-developed simple {100}, {011}, and {201} faces. In some cases, new ({111} and (031)) faces arise. Some distortion of crystals caused by their pulling in the [101] direction is observed.     

Growth of α-NiSO<Subscript>4</Subscript> · 6H<Subscript>2</Subscript>O crystals at high rates

The high-rate growth of nickel sulfate hexahydrate NiSO₄ · 6H₂O (α-NSH) crystals up to 120 × 120 × 65 mm³ in size is described for the first time. The data on the distribution of related impurities in the {011} and {001} growth sectors of α-NSH crystals grown at different rates are reported. The transmission spectra of both growth sectors of these crystals are obtained. The structural quality and the optical properties of rapidly and slowly grown α-NSH crystals are compared. It is established that the {011} growth sector of crystals grown at rates exceeding 5 mm/day shows the best characteristics for application in UV filters.     

Ferrous Tartrate recognition of sodium chloride {111} and its effect on crystal growth

The surface morphology and growth pattern of some molecules could be altered by the recognition of ferrous tartrate (FeC₄H₄O₆, FeTA). We have explored this phenomenon in the aspect of growth rate and morphology alteration of sodium chloride crystals where few researches have been done. In this paper, the crystallization behavior of NaCl with added FeTA was studied by supersaturation test, conductivity, scanning electron microscopy (SEM), and X‐ray diffraction (XRD). The results showed that the supersaturation of NaCl solution could be increased to about 5.5 % in presence of FeTA prior to the onset of crystallization. Furthermore, SEM images and XRD results indicated that the addition of FeTA could change the morphology of NaCl crystal from cubic to octahedron by impeding the growth of {111} and {110} faces. Besides, the interaction between NaCl {111} face and FeTA was discussed and the possible spatial structure of FeTA was speculated through the lattice parameters of NaCl.     

Direct Growth of Aggregates on {110} Faces of Cadmium Mercury Thiocyanate Crystals

New growth phenomena ‐ direct incorporation of aggregates have been observed on the {110} faces of cadmium mercury thiocyanate CdHg(SCN)₄ crystals by atomic force microscopy. These aggregates grow in two forms: some directly cover up the steps and forms new growth layers; while others are just incorporated at the step edges. These aggregates, which are mostly oriented along [111] direction, are formed by small columnar structural units. The aggregates have the similar structure of CdHg(SCN)₄ crystals and greatly vary in nature with the variation of solution supersaturation σ and growth time t. With the increase of σ the aggregates become larger, consistent with the variation of growth units dimension with the supersaturation; and with the increase of growth time the aggregates become more structurally substantial. These observations have led to a new understanding about the crystal growth.     

Zur Realstruktur von Ga1–xInxAs LPE-Schichten

Ga_1–xIn_xAs epitaxial layers (0.02 ≦ × ≦ 0.12) are grown on (111)-oriented GaAs substrates from nonstoichiometric melts. The etch pit densities – determined by chemical etching – yield values between 2 · 10⁵ cm⁻² and 3 · 10⁷ cm⁻² and were found to be dependent on composition, layer thickness and cooling rate. X-ray topography of cleaved {110}-planes gives information on layer quality and indicates the existence of stress in the substrate lattice near the heterojunction. The validity of Vegard's law in the investigated concentration range was confirmed by X-ray determination of the lattice constants. The half width of double crystal spectrometer rocking-curves, the epd and the relative intensity of photoluminescence show similar dependence on the composition of the mixed crystal layers.     

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.     

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.     

Growth and morphological study of copper oxide single crystals

Experiments on the growth of CuO single crystals by crystallization from flux in the CuO-Bi₂O₃-PbO-PbF₂, CuO-Bi₂O₃-Li₂O, CuO-Bi₂O₃-B₂O₃, CuO-BaO-Y₂O₃, and CuO-MO_x systems (M = P, V, or Mo) have been performed. The best results were obtained in crystallization in the CuO-Bi₂O₃-PbF₂ system: prismatic single crystals of platelet-and needlelike or isometric habit with dimensions up to 1 × 10 × 10, 1 × 1 × 20, or 6 × 6 × 8 mm, respectively, have been grown. The CuO crystals show polysynthetic twinning in the form of numerous alternating light and dark bands bound by systems of parallel straight lines on the {110} and {111} faces. A possible model of twinning associated with the Cu₂O → CuO transformation is considered.     

Solution growth and morphology of CH3NH3PbBr3 single crystals in different solvents

In this work, large‐sized CH₃NH₃PbBr₃ single crystals were successful grown using solution evaporation method with hydrohalic acid and N, N‐Dimethylformamide (DMF) as solvent respectively. The lattice parameters of cubic CH₃NH₃PbBr₃ were estimated using XRD method. The solubility of CH₃NH₃PbBr₃ in hydrobromic acid was determined at the temperature range between 20 °C–90 °C. A special micro‐solution crystallizer was designed to in‐situ study the morphology of CH₃NH₃PbBr₃ crystal. The largest crystal face was indexed by the XRD patterns and it would be {110} for CH₃NH₃PbBr₃ grown from HBr solution and {100} from DMF solution. The results show that solvent would affect the morphology and crystal habit greatly during crystal growth from solution.     

Electric conductivity and lattice disorder of PbMoO4 crystals

From differential thermal analysis (DTA), thermal etching, perfectly reversable redox treatments and electric conductivity it is concluded that the Pb/Mo ratio of the PbMoO₄ crystals is always 1 and that phase transitions do not occur. Pb³⁺ ions detectable by an absorption band at 435 nm cause a p-conductivity due to the reaction Pb³⁺ ⇌ Pb⁺⁺ + e⁺. At elevated temperatures the p-conductivity increases with increasing oxygen partial pressure of the surrounding atmosphere. The influence of foreign ions on the concentration of ionic and electronic defects in PbMoO₄, CaMoO₄, PbO, and PbTiO₃ can be explained by an anti-Frenkel disorder of the oxygen ion sublattice. For PbMoO₄ crystals the mobility O⁻ ion vacancies and the free formation enthalpy of anti-Frenkel defects are found to be v_v = \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop - \limits_T^{9160} $\end{document} exp (−1.15 eV/kT) cm² K/Vs and g_AF = 3.6kT −2.2 eV, respectively.     

Crystallization of inorganic salts from aqueous solutions in a microwave field

The crystallization of some inorganic salts (KH₂PO₄, NaCl, Sr(NO₃)₂, KNO₂, Ca(OH)₂) by the thermal-gradient (with decreasing temperature) and solvent-evaporation methods using microwave heating of solutions is investigated. It is established that the growth rates of single crystals in a microwave field are an order of magnitude higher than obtained in other known techniques at comparable crystallization temperatures and supersaturations. For example, the growth rate of prismatic faces {100} of KH₂PO₄ crystals is as high as 11 mm/day at supersaturations of ～1.2%. The results obtained are discussed in the context of the effect of microwave radiation on the adsorption surface layers of crystals. Fine-grained phases of the salts under study are obtained by evaporation of the solvent.     

Synthesis and characterization of a new nonlinear optical single crystal: L‐Lysinium trifluoroacetate

Single crystals of a new L‐Lysine salt: L‐Lysinium trifluoroacetate {abbreviated as LLyTFA; [(NH₂)‐(CH₂)₄‐CH‐(NH₃)‐(COOH)]⁺ CF₃COO^‐} were grown by slow evaporation of an aqueous solution at room temperature. The grown crystals were subjected to single crystal X‐ray diffraction, FTIR and UV‐Vis‐NIR spectrum analyses. The UV‐Vis‐NIR spectrum shows that the absorption is very less in the whole of the region from ultraviolet to near IR. The Kurtz‐Perry powder SHG measurement using a Nd:YAG laser of wavelength 1064nm confirms the frequency doubling of the crystal and its powder SHG efficiency was measured as d_eff = 0.96 d_eff (KDP). (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study on the Growth of Triglycinsulphate Single Crystals

Crystallization of TGS at 52.0°C - above the transition point - has been studied in a wide range of supersaturation of the solution (σ = 0 to 10⁻²). The rates of growth of {110} and {001} faces were measured as a function of supersaturation at constant hydrodynamical conditions (Re = 3.4 · 10⁻³). Further, the influence of hydrodynamical conditions on the growth of {110} faces at constant supersaturation (σ = 4.2 · 10⁻³) was established. The parameters of the experimentally found dependences are determined on the basis of the surface-diffusion model of BURTON . CABRERA and FRANK . From these dependences follows that the growth rate of the {110} faces is already almost limited by the volume diffusion of TGS molecules towards the crystal surface, while in the case of {001} faces the surface diffusion mechanism of crystallization is clearly manifested. Dislocation densities in the crystals have been determined by means of etching technique. The number of dislocations increases with increasing supersaturation; hence, supersaturation of the solution together with the processes taking place in the regeneration zone surrounding the seed determine the number of dislocations in the crystal volume and thus the resulting structural perfection of single crystals. Investigation of the spontaneous redistribution of domains showed that the growth rate of TGS crystals influences the dielectric properties to much smaller extent than does chemical purity.     

Growth Mechanism and Twinning of Sucrose Effected by Surface Adsorption Processes

Growth experiments with sucrose dependent on temperature and supersaturation of solutions were carried out to find the conditions for appearance of the three different growth types. Measurements of growth rates of {110} and {1 1 0} faces at 50°C and supersaturation c_s = 10% resulted in the known feature that in pure solutions a crystal grows faster in positive b-direction than in the negative one. Addition of raffinose stopped growth of {110}. In an electric field generated by 20 kV direct voltage (crystal orientation: negative pole of b-axis pointed towards the negative electric pole) the crystal grew in negative b-direction three times faster than in the positive one. In the presence of raffinose the growth rates in both directions become equal. If the crystal is turned by 180° in the solution (pure solution and in the presence of raffinose) the growth behaviour is the same as without an electric field. These results can be interpreted in such way that in pure solutions sucrose molecules adsorb to {1 1 0} (bonds exist between the fructose rings of molecules in liquid and solid phases) and that in presence of raffinose these molecules adsorb to {110} (bonds exist between glucose (solid) and galactose rings (liquid phases)). By the electric field the adsorption is hindered. The theory is in accordance with the fact that crystals situated in a suspension of the solution can intergrow with a host crystal in twin positions (in pure solutions on {1 1 0} and in the presence of raffinose on {110}).     

Semiopen Physical Vapour Transport Growth of Urotropine Crystals

It is reported for the first time the growth of urotropine (HMT) crystals by a semiopen physical vapour transport (SOPVT) technique. HMT crystals, approximately 1 cm³ in volume, are grown on a glass pedestal from solution-grown seeds. The final habit of the crystals is limited by rhomboedrical {110} faces which develop on an otherwise hemispherical shape. Preliminary X-ray diffraction investigations (rocking curves and topographs) point to a still non-homogeneous crystal structure, which very likely originates at the seed-crystal interface. However, in comparison with solution-grown samples, the best structural quality was observed in a SOPVT-grown sample.