Showing papers in "Crystal Research and Technology in 1996"

Effects of rare-earth ions on the quality of a Li-Zn ferrite

Abstract: Effects of the rare-earth ions on some properties of a lithium-zinc ferrite used in high frequency are described. A set of seven compounds with formula Li0.3Zn0.4Fe1.96R0.04O4 where R Yb, Er, Dy, Tb, Gd, Sm and Ce, were prepared by the classical method. The obtained results reveal that, by introducing a relatively small amount of R2O3 instead of Fe2O3, an important modification of both the structure and the properties can be obtained. Curie point, magnetization, electrical resistivity, density, hardness are affected by these substitutions. The effects of rare-earth ions were explained both by their partial diffusion in the spinel lattice and by the formation of the crystalline secondary phases on the grain boundaries. Densification of the ceramic is attributable predominantly to the relative shrinkage during sintering. Le travail montre les effets des ions de terre rare sur quelques parametres d'nne ferrite de LiZn utilise dans la haute frequence. Une serie des sept compositions avec la formule chimique Li0.3Zn0.4Fe1.96R0.04O4 (R Yb, Er, Dy, Tb, Gd, Sm et Ce) a ete preparee par la methode classique. Les resultants obtenus montrent que par l'introduction des petites quantites de R2O3 dans le lieu de Fe2O3 une important modification tant de la structure que des proprietes on peut obtenir. La temperature de Curie, l'aimantation, la resistance electrique et densite sont affectes. L'influence des ions de terre rare este explique tant par leur partiel diffusion dans la reseau spinel que par leur segregation a la surface des cristaux comme phases secondaires. La densification du ferrite est atribue en principal a une relative contraction pendant le frittage.

Static disorder in hexagonal crystal structures of C60 at 100 K and 20 K

Abstract: C60 · 2C8H10 (100 K): hexagonal space group P63, a = 23.694(4), c = 10.046(2) A, V = 4884(2) A3, Dx = 1.903 g cm−3, Z = 6, F(000) = 2856, γ(CuKa) = 1.54178 A, μ = 0.84 mm−1. C60 · 2C8H10 (20 K): hexagonal space group P63, a = 23.67(1), c = 10.02(1) A, V = 4862(6) A3, Dx = 1.912 g cm−3, Z = 6, F(000) = 2856, γ(CuKa) = 1.54178 A, μ = 0.84 mm−1. The structures were determined by Patterson syntheses and rigid-body refinements. The C60 molecules show two orientations with one molecular centre in common. The solvent molecules are disordered too. Static disorder could not be overcome or influenced by cooling down. A coordination number of 10 was found for the fullerene molecules. Kristalldaten: siehe oben. Die Strukturen wurden durch Patterson-Synthesen und Rigid-Body-Verfeinerngen bestimmt. Die C60- Molekule zeigen zwei Orientierungen mit einem gemeinsamen Molekulzentrum. Die Losungsmittelmolekule sind ebenfalls fehlgeordnet. Tiefe Temperaturen konnten die statische Fehlordnung nicht verhindern oder beeinflussen. Fur die Fulleren-Molekule wurde eine Koordination von 10 gefunden.

Influence of the pH‐Value on the Growth and Dissolution Rate of Potassium Chloride

Abstract: A fluidized bed crystallizer is employed to investigate the effect of pH of the solution on the growth and dissolution rates of potassium chloride crystals. The growth rate shows a minimum value at the pH range between 7 and 10, whereas the dissolution rate shows a minimum at the range between 7 and 9. It is found in this study that the growth- and the dissolution rate of potassium chloride in the acidic solutions are higher than in the alkaline solutions. A mechanism is suggested to explain the growth kinetics based on the interaction between the different species found in the electrolyte solution.

Gravitational Effects on Mixing and Growth Morphology of an In0.5Ga0.5 System

Abstract: A mixing experiment of multicomponents melts was performed using a uniform temperature furnace in the Second International Microgravity Laboratories (IML-2) mission. Growth morphologies and Ga concentration profiles were analyzed for the samples with the compositional ratio of 0.5 In–0.5 Ga–1.0 Sb grown under microgravity and on earth. The sample with free surface grown under microgravity was nearly spherical in shape, except some parts with projections. Ga was dispersed homogeneously in the bulk because the mixing was enhanced by Marangoni convection due to the concentration gradient. On the other hand, the sample grown on earth was a double cylindrical shape with different diameters, and Ga concentration decreased from top to bottom, showing clearly the effect of gravity. Many needle crystals were formed in both space and earth samples due to rapid cooling. The average size of the needle crystals grown in space was larger than that of the earth sample.

Transport Coefficients of (Bi1‐xSbx)2Se3 Single Crystals

Abstract: (Bi 1-x Sb x ) 2 Se 3 (x =00 to 02) single crystals were prepared using a modified Bridgman method Measurements of the Hall coefficient R H , electrical conductivity σ and Seebeck coefficient a showed that incorporation of the antimony atoms into the Bi 2 Se 3 crystal lattice results in an increase in the free electron concentration for a low antimony content, whereas the free electron concentration is suppressed in the range of a high antimony content This effect is explained qualitatively by changes in the concentrations of point defects in the (Bi 1-x Sb x ) 2 Se 3 crystals We assume that the substitution of Bi atoms by Sb atoms results in a decrease in the concentration of Se vacancies V Se and antisite defects Bi' Se The course of the dependences of In (R H σ) vs ln T manifests that in the temperature region of 100-400 K transport properties of the studied crystals are characterized by a mixed transport mechanism of free carriers, mainly on acoustical phonons and ionized impurities

Effect of Supersaturation and Temperature on the Growth Morphology of Ammonium Oxalate Monohydrate Crystals Obtained from Aqueous Solutions

Abstract: The experimental results of a study of the effect of supersaturation and temperature on the growth morphology of ammonium oxalate monohydrate [(NH 4 ) 2 C 2 O 4 H 2 O; AO] single crystals obtained from aqueous solutions at 30 and 40 °C and supersaturation up to 9% are presented The observations are analysed in terms of theoretical morphology, growth models and attachment energy for growth units in steps of growing faces

Studies on the Structure of alpha‐Quinacridone

Abstract: Alpha-quinacridone crystallizes in the triclinic space group P1 with Z = 2, a = 14.934 ± 0.064 A, b = 3.622 ± 0.004 A, c = 12.935 ± 0.040 A; α = 91.39 ± 0.28°, β = 107.13 ± 0.02°, γ = 92.84 ± 0.24°. The molecules are connected by hydrogen bonds more far from linearity (≈145°) than gamma-quinacridone 162°). Together with π-π bonds, building molecular stacks along the short axis b = 3.622 A, both types of bonds run through the whole lattice. Molecules within the hydrophobic planes exhibit orientational disorder. Transitions between gamma- and alpha-quinacridone has been discussed: all inversion centers are retained, only the vectors of bravais lattice and the angles of molecules in the stacks are changed. The calculated pattern of alpha-quinacridone is compared with the experimental one by means of overlay- and difference plots. – The transition character of the alpha-quinacridone is stressed by generation of a combined pattern of 50% alpha- and 50% gamma-quinacridone, calculating an experimental alpha-quinacridone. Die Kristallstruktur von alpha-Chinacridon wird triklin, Raumgruppe P1, Z = 2, mit a = 14.934 ± 0.064 A, b = 3.622 ± 0.004 A, c = 12.935 ± 0.040 A; α = 91.39 ± 0.28°, β = 107.13 ± 0.02° und γ = 92.84 ± 0.24° beschrieben. Die beiden Molekulhalften der asymmetrischen Einheit sind durch starker gewinkelte NHO-Wasserstoffbrucken (≈145°) verbunden als im gamma-Chinacridone (≈162°). Zusammen mit π-π-Bindungen, die entlang der kurzen Achse b = 3.622 A Molekulstapel aufbauen, ziehen sich beide Bindungstypen durch das Gitter hindurch. Molekule innerhalb der hydrophoben Flache haben Orientierungsunordnung. Ubergange zwischen gamma- und alpha-Chinacridon werden diskutiert: alle Inversionszentren der Molekule fallen mit solchen des Bravaisgitters zusammen. Nur die Vektoren des Bravaisgitters und die Winkel der Molekule in den Stapeln werden geandert. – Das berechnete Diagramm von alpha-Chinacridon wird mit dem experimentellen Diagramm durch Overlay- und Differenzplot verglichen. Der Ubergangscharakter des alpha-China-cridons wird durch Erzeugen eines kombinierten Diagramms von 50% alpha- und 50% gamma-Chinacridon betont, das ein experimentelles alpha-Chinacridon berechnet. Im Handel vorkommende, aber auch im Technikum oder Labor hergestellte Pigmentproben enthalten wahrscheinlich immer anteilig die andere Phase: gamma-QA enthalt Anteile von alpha-QA, alpha-QA enthalt Anteile von gamma-QA.

Thermal Analysis of LiGaO2 and NaGaO2

Abstract: The high-temperature thermal properties of the ternary oxides LiGaO2 and NaGaO 2 are studied by simultaneous differential thermal analysis and thermogravimetry between room temperature and about 1700°C. For the melting temperature of LiGaO 2 a value of 1595 ± 10°C is determined. NaGaO2 undergoes a solid state phase transition at 1280 ± 10 °C and melts at 1395 ± 10 °C.

Growth and characterization of urea-(DL) tartaric acid single crystals

Abstract: A new organic UV nonlinear optical crystal urea-(DL)tartaric acid [CO(NH2)2−(DL) C4H6O6] (abbreviated as U(DL)T) is reported. Large single crystals have been grown from aqueous solution by the cooling method. They belong to the monoclinic space group P21 and the lattice parameters are: a = 7.6973 A, b = 23.3310 A, c = 4.8727 A, and β = 100.82°. The structure and some of its physical properties have been determined. The crystal is transparent from 0.24 to 1.95 μm. The efficiency of powder SHG is larger by one order of magnitude than that of KDP. Thus the crystal will be a useful NLO material.

Structure and Texture of Nickel‐Molybdenum Catalysts on Alumina Support Modified with Fluoride or Chloride Ions

Abstract: The performed study involves measurements of a specific surface area via a BET method, of the pore volume, FT-IR, and a derivatographic study of a series of Al 2 O 3 -supported nickel-molybdenum catalysts modified with fluoride and chloride ions. It was found that fluoride ions lead to a decrease in the specific surface area of catalysts, whereas chloride ions have a small effect on this parameter. Modification does not change the type of pores of the catalysts, yet it affects their size and increases concentration of OH groups adsorbed on the surface of the catalysts relative to the carrier and the unmodified catalyst. Addition of fluoride ions decreases the thermal stability of the catalyst, whereas chloride ions does not cause any change.

Hardness studies and fracture behaviour on flux-grown YFeO3 single crystals

Abstract: Results of Vickers' microhardness (H v ), fracture toughness (K c ), brittleness index (B i ) of (110) and (001) faces of flux-grown yttrium orthoferrite crystals, in the load range of 10-100 g, are given. The cracks are classified into Palmqvist and median types. The transition from Palmqvist to median type of cracks is shown to take place when the applied load exceeds 50 g. Application of the formula of NIHARA et at. for only median cracks leads to calculation of more precise values for fracture toughness and brittleness index than what was reported earlier (BAMZAI et al.) as an average value.

Anisotropy of Electrical Resistivity and Hole Mobility in InTe Single Crystals

Abstract: The temperature dependences of the electrical resistivity and Hall mobility of ptype InTe chain single crystals in parallel and perpendicular directions to c-axis have been investigated in the temperature range of 28-260 K. The high anisotropy between ell and el which depends on temperature is attributed to high concentration of stacking faults due to weak interchain bonding. The mobility parallel to c-axis was found to vary with temperature as ,u 0: Ic" where n = -0.6 due to hole scattering on polar optical phonons. The mobility perpendicular to c-axis above 140 K increases with temperature exponentially with an activation energy of 0.03 eV which is attributed to the hopping mechanism due to the barriers between the chains.

Validity of the Lattice‐Parameter Vegard‐Rule in Cd1‐xZnxTe Solid Solutions

Abstract: Cd1-xZnxTc crystals of different composition (0 ⩽ x ⩽ 1) were grown by the vertical Bridgman method and by synthesis in Te excess. After careful surface preparation of crystal slices, their Zn:Cd ratios were ascertained by wavelength-dispersive X-ray spectroscopy (WDXS), and the lattice parameters of the same slice regions were measured by X-ray diffractometry. The Vegard rule concerning the linear lattice-parameter dependence on composition is – in contrast with earlier literature data – exactly valid within the limits of error (Δx ⩽ ±0.01 and Δa/a ⩽ 3.7. 10−4) and follows the equation a(x) = (0.64822 - 0.03792x) nm. After annealing some slices at different temperatures and controlled partial pressure conditions in ordcr to find possible phase separations or cation ordering effects, neither the lattice parameters were changed nor additonal interferences were found. A published occurrence of a rhomhohedral phase could not be confirmed by means of powder diffraction analysis. The results are discussed in relation to own electron diffraction investigations and to EXAFS literature data. Cd1-xZnxTe-Kristalle verschiedener Zusammensetzungen (0 ⩽ x ⩽ 1) wurden nach dem vertikalen Bridgmanverfahren und mittels Synthese bei Te-Uberschus gezuchtet. Nach sorgfaltiger Oberflachenpraparation der Kristallscheiben wurde das Zn: Cd-Verhaltnis mittels wellenlangendispersiver Rontgenspektroskopie bestimmt. Die Gitterparameter wurden an denselben Stellen rontgendiffrakto metrisch gemessen. Die Vegard-Regel uber den linearen Zusammenhang Gitterparameter-Zusammensetzung ist – im Gegensatz zu fruheren Literaturergebnisse – exakt innerhalb der Fehlergrenzen (Δx ⩽ ±0.01 und Δa/a ⩽ ±3.7. 10−4) gultig: a(x) = (0.648322 - 0.03792x) nm. Mit dem Ziel, Phasenseparationen oder Ordnungseffekte nachzuweisen, wurden einige Proben unterschiedlich getempert. Die Gitterparameter anderten sich aber nieht, ebenso wurden keinen zusatzlichen Interferenzen gefunden. Das publizierte Auftreten einer rhomboedrischen Phase konnte bei pulverdiffraktometrischen Untersuchungen nicht bestatigt werden. Die Ergebnisse werden im Zusammenhang mit eigenen Elektronenbeugungsuntersuchungen und EXAFS-Literaturdaten diskutiert.

XRD line broadening studies on mullite

Abstract: An X-ray diffraction microstructural study on 110, 220, 001 and 111 peaks has been performed on mullite in the temperature range of primary mullite formation in order to monitor nucleation and growth process. Considering the crystallinity of the starting kaolinites, a greater disorder of the kaolinite has been found to enhance the mullite formation. Isothermal growth is related to a decrease in the Al 2 O 3 content of mullite.

Crystal Structure Investigation of 2‐Pheny limidazo [f]1,10‐phenanthroline

Abstract: The crystal structure of the title compound (PIP) has been determined by single crystal X-ray diffraction methods. C 19 H 12 N 4 .C 2 H 5 OH crystallizes in the monoclinic space group P2 1 /n with a = 11.4414(8), b = 12.6052 (9), c = 12.4627(8) A, β = 100.345 (2)°, Z = 4, V= 1768.17 A 3 , D cal = 1.286 Mg. m -3 , μ (MoKa) = 0.80 cm -1 , F(000) = 720. The structure was solved by the direct methods and refined by full-matrix least-squares method to a final R = 0.0337 and R w = 0.0332 for 2306 reflections with F 0 > 4σ(F 0 ). The phenyl ring and the imidazo[f]1,10-phenanthroline moiety are coplanar in the crystal. The packing of the molecules involves hydrogen bonded association of the hydroxyl group of ethanol both with the N-H of the imidazole moiety of one PIP and one nitrogen atom of the phenanthroline moiety of another PIP.

Crystal structure of sarcosine cadmium chloride

Abstract: Single crystals of sarcosine cadmium chloride were crystallised from a saturated aqueous solution containing stoichiomeric amounts of sarcosine and cadmium chloride, in 1:1 proportion. The intensity data were collected using a CAD-4 diffractometer with graphite monochromated MoK α radiation. The crystal data are as follows: a = 6.916(1) A, b = 13.855(3) A, c = 7.981(1) A, V = 764.1 A. F.W. = 272.4, d expt = 2.39 g.cm -3 , d calc = 2.368 g.cm -3 , Z = 4 and the space group is P2 1 /n. The structure has been solved to an R value of 0.023 for all the 1323 reflections with I > 2σ(I). The sarcosine molecule exists as zwitterion in the structure. The conformation of the sarcosine molecule is significantly changed due to the complexation of the molecule with cadmium chloride. The cadmium ion is found to have an octahedral coordination with both the oxygens of the carboxyl group of the amino acid and chlorines taking part in it. Since the complex has no water of hydration, only two hydrogen bonds of the types N-H..O and N-H..Cl are found.

Electrical Conductivity in Polycrystalline Copper Oxide Thin Films

Abstract: This study presents a preliminary investigation on the electrical properties and the electronic structure of the copper-oxygen system. Thin films, prepared by high vacuum sputtering on glass and MgO substrates, were oxidised both at constant temperatures and by heating continuously from a low to a high temperature, and the variations in the resistance with oxidation were measured. The final oxide was found to be CuO. The room temperature resistance after oxidation is very much higher than that before oxidation, indicating a transition from metal to insulator. At oxidation temperatures below 600 K, the conductivity decreased gradually; a steeper decrease occurred at higher temperatures when an apparent semiconducting behaviour was observed in some cases. At temperatures above 600 K, the behaviour of the conductivity followed the form σ(T) = σ(0) + αT β , which suggested weak localization or electron-electron interaction.

Control of the Growth Optimum in Producing High‐Quality CaF2 Crystals by an Improved Bridgman‐Stockbarger Technique

Abstract: The axial temperature distribution in an empty crucible and the determination of quenched interface within fixed crucible were investigated to find the relationships governing the growing process of CaF 2 by Bridgman-Stockbarger methods. A system of additional molybdenum reflective sheaths was placed into the furnace unit and its effect on the temperature field was estimated in order to achieve the growth optimum. A long liner into the diaphragm bore of the furnace and a number of thin rings slipped on the crucible stem were found capable to provide a reproducible optimum on each stage of growing in single and multicamera crucibles at a relatively low level of power supply. Single and ingroup growth experiments were carried out using high density quenched ingots purified from oxygen contaminants through high temperature treatment of fluorspar. The properties of the grown crystals were found to depend on the degree of the fluorspar purification and on the improvement of the thermal conditions yielding either competitor or laser-grade CaF 2 . In multicamera crucibles the crystals grown in the central compartment are of better characteristics than those in the peripheral ones.

VLS Growth of ITO Whiskers Prepared by the Electron Shower Method

Abstract: Indium tin oxide (ITO) whiskers were grown by VLS (vapour-liquid-solid) mechanism, using the electron shower method. The whiskers were grown above 200 °C, and the deposition rate was above 0.6 nm/s. The electron shower controlled the size of the whiskers, and the size was 30 nm in diameter and 600 nm in length. The whiskers grew along the substrate at t 300 s. When the ITO whiskers grown along the substrate were used as NO2 gas sensor, the sensitivity was 340, and about 300 times higher than those of the whiskers grown in a direction perpendicular to the substrate and plate-like ITO crystallites.

Long-term Crystal Growth under Microgravity during the EURECA-1 Mission (I) THM Growth of AlxGa1−xSb

Abstract: Long-term crystal growth experiments were successfully performed under microgravity conditions during the first flight of the unmanned mission EURECA-1 in the automatic mirror furnace (AMF). Two crystals of Al x Ga 1-x Sb with [001] and [111] orientation respectively were grown from gallium solution by the travelling heater method. The grown length of the single crystals is 4.0 mm and 4.2 mm respectively. The space-grown samples show a high microscopic homogeneity which indicates the absence of time dependent convection. From pulse markers a constant growth rate of 0.6 ± 0.1 μm/min is measured which is lower than 0.8 ± 0.1 μm/min obtained in earth grown reference samples. Details about the experiment performance and the growth results are given.

Sb2Te3 single crystals doped with chromium atoms

Abstract: Chromium-doped Sb2Te3 single crystals were prepared from elements of semiconductor purity using a modified Bridgman method. The samples of these crystals were characterized by means of X-ray diffraction analysis, measurements of the reflectivity in the plasma resonance frequency range ωp, of the Hall constant RH and electrical conductivity σ. It was found that the incorporation of Cr atoms into the Sb2Te3 crystal lattice reduces the volume of the unit cell, whereas the values of ωp and RH (i.e. the concentration of holes) remain unaltered and the values of σ decrease with increasing chromium content. This effect is qualitatively explained by an interaction of incorporated Cr atoms with antisite defects of Sb2Te3 crystal lattice. The In (RHσ) vs. In T dependences show that the dominant mechanism of scattering of free charge carriers in the studied crystals is the scattering by acoustic phonons; the presence of chromium atoms increases the scattering rate by ionized impurities. Die mit Cr dotierten Sb2Te3-Einkristalle aus den Elementen mit Halbleiterreinheit wurden mit einer modifizierten Bridgman-Methode gezuchtet. Ihre Charakterisierung erfolgte mit Hilfe der Rontgenbeugungsmethode, der Hall-Konstanten RH, der elektrischen Leitfahigkeit σ und der Reflektivitat im Gebiet der Plasma-Resonanzfrequenz ωp. Es wurde festgestellt, das der Einbau der Cr-Atome im Sb2Te3 Kristallgitter die Volumenabnahme der Elementarzelle verursacht; die Werte von ωp und RH bleiben unverandert, die elektrische Leitfahigkeit nimmt mit zunehmendem Cr-Gehalt ab. Dieser Effekt wird mit Hilfe eines Modells erklart, das die Existenz von Antistrukturdefekten im Sb2Te3 Kristallgitter annimmt. Die Abhangigkeiten In (RHσ) vs. In T zeigen, das der uberwiegende Streuungsmechanismus der freien Ladungstrager der Streuungsmechanismus der akustischen Phononen ist; die zunehmende Cr-Dotierung fuhrt zu der Zunahme des Anteils des Streuungsmechanismus an ionisierten Storstellen.

A Simple Model for Evaluation of Electronic Polarizabilities of Chalcopyrity Semiconductors

Abstract: Simple correlations between the energy gap, optical electronegativity and the refractive index are given for some ternary chalcopyrite semiconductors. Refractive indices and electronic polarizabilities are evaluated. Results are in good agreement (±5.3%) with the experimental values, better than those of the values (±19.5-28%) rising bond charge model and plasma frequency formalism.

Thermodiffusion and morphological stability in convectionless crystal growth systems from melts and melt-solutions

Abstract: Crystal growth experiments of multicomponent systems under microgravity require an exact analysis of the diffusion phenomena in the nutrient fluid phase. The contribution of the Soret effect to the transport and distribution of matter in a convectionless casting arrangement for shaped crystal growth and in THM melt-solution zones have been investigated. Some semiconductor systems were analysed from experimental (Bi1-xSbx mixed crystals) and theoretical (PbTe, InP, GaAs, CdTe compounds) point of view. The criterion for constitutional supercooling was correspondingly modified. It has been distinguished between associated (AIVBVI, AIIBVI) and dissociated (AIII–BV) melt-solutions, containing different species of diffusion (molecules or atoms, respectively). Kristallzuchtungsexperimente mit mehrkomponentigen Systemen unter Schwerelosigkeit erfordern cine exakte Behandlung der Diffusionsphanomene in der fluiden Nahrphase. Es wurde der Beitrag des Soret-Effektes zum Massetransport und zur -verteilung in einer konvektionsfreien Giesanordnung zur Zuchtung von Formkristallen und in THM-Schmelzlosungszonen untersucht. Dazu wurden einige Halbleitersysteme experimentell (Bi1-xSbx Mischkristalle) und theoretisch (PbTe-, InP-, GaAs-, CdTe-Verbindungen) uberpruft. Das Kriterium fur Konzentrationsunterkuhlung wurde entsprechend modifiziert. Es wurde zwischen assoziierten (AIV–BVI, AII–BVI) und dissoziierten (AIII–BV) Schmelzlosungen unterschieden, die unterschiedliche Diffusionsspezies (Molekule bzw. Atome) aufweisen.

A Novel Structure of Bipyridine Coordinated with Copper (II): [Cu(bipy) (H2O)3] · (NO3)2

Abstract: The crystal structure of the mononuclear copper (II) complex containing a 2,2'-bipyridine and three water molecules, [Cu(bipy) (H 2 O) 3 ]. (NO 3 ) 2 , is reported. The copper coordination polyhedron is a five-coordinated distorted pyramid.

XPS Analysis of Bridgman‐grown CuInTe2 and of its Native Oxide

Abstract: X-ray excited photoelectron spectroscopy is used to analyse the near-surface properties of CuInTe 2 single crystals grown by the vertical Bridgman method. It is found that keeping the crystals at room temperature in air for relatively short times is sufficient for the formation of an oxide layer which consists mainly of TeO 2 . No detectable amounts of copper or indium oxides could be observed.

A New Molecular Crystal: Urea Tartrate

Abstract: Urea tartrate, CO(NH 2 ) 2 (+)C 4 H 6 O 6 (hereafter abbraviated as UT) is reported for the first time Large Single Crystals have been grown by the cooling method from aqueous solution Some of its physical properties have been measured The second harmonic generation of powder specimens is about three times larger than that of KH 2 PO 4

In Situ Observation of Step Evolution on {100} Face of KH2PO4 Crystal in Solution by Atomic Force Microscopy (AFM)

Abstract: In situ observation of the surface morphology of {100} face of Potassium Dihydrogen Phosphate (KDP) crystals growing in solution was made with the use of Atomic Force Microscope. The slight movement of the steps connected with regeneration of the crystal surface has been detected for very low supersaturation. The height of the elementary steps has been established.

The Thermal Decomposition of Polyhalite K2SO4 · MgSO4 · 2 CaSO4 · 2 H2O

Abstract: The thermal decomposition of polyhalite (K2SO4 · MgSO4 · 2 CaSO4 · 2H2O) was investigated by DSC/TG and X-ray powder diffraction. The decomposition of the polyhalite starts at 285 °C in releasing the crystal water within one step. Simultaneously the decomposition of the polyhalite into anhydrite and two solid solutions of the compositions K2SO4 · 1.76 MgSO4 · 0.24 CaSO4 and K2SO4 · 0.64 MgSO4 · 1.36 CaSO4 is taking place. The mechanism of decomposition runs through K2SO4 · MgSO4 CaSO4. This phase reacts immediately to the solid solutions, mentioned above. Die thermische Zersetzung von Polyhalit (K2SO4 · MgSO4 · 2CaSO4 · 2H2O) wurde mittels DSC/TG und Rontgenpulverdiffraktometrie untersucht. Die Zersetzung des Polyhalits beginnt bei 285 °C mit der Abspaltung des Kristallwassers in einem einstufigen Prozes. Gleichzeitig kommt es zur Zersetzung des Polyhalits in Anhydrit und zwei Mischkristalle der Zusammensetzung K2SO4. 1,76 MgSO4.0,24 CaSO4 und K2SO4.0,64 MgSO4 · 1,36 CaSO4. Der Zersetzungsmechanismus verlauft uber K2SO4. MgSO4. CaSO4. Diese Phase zerfallt dann unmittelbar zu den oben angefuhrten Mischkristallen.