Formation of inclusions in CaF2 single crystals

It is reported on formation of inclusions during the Stockbarger growth of CaF₂. It the centre of this paper, hollows (gaseous or vacuum inclusions) are considered. Two different kinds of formation processes being possible under special growth conditions are discussed (segregation of gaseous impurity, entrapment of impurity-rich liquid at cell boundaries of growth cells).     

Formation of atomic solution in liquid eutectic alloys

The influence of Pb, In, Bi and Ge on structure of tin within 0–12.5 at.% concentration range has been studied by means of X-ray diffraction method. Samples were prepared by melting in vacuum furnace filled with pure argon from ingots of Sn(99.999%), Pb(99.99), In(99.999), Bi(99.99), Ge(99.999) and checked by means of X-ray microanalysis The structure factors and pair correlation functions were analyzed. Concentration dependencies of structure parameters for liquid Sn-enriched melts in binaries with eutectic point are described. It is shown that atomic arrangement in tin-based molten alloy deviates from random atomic distribution within concentration range where these alloys can be considered as diluted solutions. Limited solubility in solid state in eutectic Sn-based systems is a precursor to deviation from random atomic distribution in liquid state.     

Quenched glasses containing lanthanum and other trivalent sulfates

A wide glass-forming region has been observed in the Li₂SO₄-La₂(SO₄)₃ system with essentially pure glass produced by roller quenching compositions of 20 to 90% Li. Even water or air quenching produced glasses. Many of these glasses showed double exotherms during crystallization and some showed glass transitions. Limited experiments also showed some glass-formation in other alkali-La sulfates, in compositions containing Y and Sc sulfates and in mixtures. Ionic conductivities and some infrared measurements are also reported.     

Formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet grown by horizontal directed crystallization method

It is shown that the formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet (YAG) grown by the method of HDC is caused by local accumulation of impurities, disturbance of morphological stability of the crystallization front and capture of inclusions and impurities in the nodal region of the melt two‐vortex convection. Studied is the influence of thermal and geometrical parameters of the melt and the shape of the crystallization front on the conditions of the formation of the capture of inclusions.     

Determination of the orthorhombic coincidence site lattice for bicrystals of any lattice system

The concept of the coincidence site lattice is generalized for bicrystals of any lattice system. Describing the formation of bicrystals by cutting the ideal lattice and rotating the partial lattices the conditions for the coincidence site lattice are presented. For the construction of the special case of orthorhombic coincidence site lattice an instruction is given.     

Formation of microtwins in TmP/GaAs heterostructures

Microtwins in semi-metal thulium phosphide (TmP) epilayers grown on (0 0 1) GaAs substrates by molecular beam epitaxy have been studied by transmission electron microscopy. Selected area diffraction patterns show extra spots along 〈1 1 1〉 and 〈2 2 4〉 corresponding to three times the normal rock-salt periodicity. Only one or two twin variants are found in the crystal. The occurrence of the observed microtwins in the TmP-GaAs heterostructure can be accounted for by the growth-accident mechanism, i.e., the formation of microtwins is via growth accidents in the stacking sequence on {1 1 1} and {1 1 2} planes. The growth accidents appear to occur due to rapid growth rates and/or contamination.     

HREM investigations of intermediate ZnO and ZnO/Y–ZrO2 layers in Y–ZrO2 bicrystals and ZnO films grown on Y–ZrO2 bicrystal substrates

The structure of yttrium-stabilized ZrO₂ (YSZ) bicrystals with ZnO and ZnO/YSZ/ZnO/YSZ/ZnO intermediate layers, as well as ZnO films grown on YSZ bicrystal (1 1 0)/90° substrates, has been investigated by means of high-resolution electron microscopy (HREM) and microanalysis. All bicrystals were produced by the solid-phase intergrowth (SPI) method. The internal ZnO film in the bicrystal formed at the SPI temperature of 1400°C consisted of domains with two symmetrical orientations: , and , . A bicrystal with a ZnO/YSZ/ZnO/YSZ/ZnO internal film was formed at the temperature of 1200°C. There was no mixing of ZnO and YSZ films and no traces of any solid-phase reactions were observed. Grains in all internal ZnO films and ZnO films grown on the bicrystal substrates had numerous stacking faults. It was found that SPI does not influence the density and structure of these defects. Orientational relationships between YSZ and ZnO in all samples were determined. The ZnO films grown on (1 1 0)/90° bicrystal substrates inherited the grain boundary (GB) from the substrate. Its structure and geometry is determined by four variants of ZnO grain growth.     

Synthesis and crystal structures of coordination compounds of pyridoxine with zinc and cadmium sulfates

The pyridoxine complexes with zinc and cadmium sulfates are synthesized. The IR absorption spectra and thermal behavior of the synthesized compounds are described. Crystals of the [M(C₈H₁₁O₃N)₂(H₂O)₂]SO₄ · 3H₂O (M = Zn, Cd) compounds are investigated using X-ray diffraction. In the structures of both compounds, the M atoms are coordinated by the oxygen atoms of the deprotonated OH group and the CH₂OH group retaining its own hydrogen atom, as well as by two H₂O molecules, and have an octahedral coordination. The nitrogen atom of the heterocycle is protonated, so that the heterocycle acquires a pyridinium character. The cationic complexes form layers separated by the anions and crystallization water molecules located in between. The structural units of the crystals are joined together by a complex system of hydrogen bonds.     

Formation of silica/epoxy hybrid network polymers

Epoxy-based inorganic–organic hybrid polymers, for use as a matrix in coatings, have been prepared from 3-glycidoxypropyltrimethoxysilane by a sol–gel process. The precursor molecule possesses both epoxy and silicon alkoxide functionality and so interlinked inorganic–organic networks can be formed. Diethylenetriamine was used to open the epoxy rings and form the organic network to an extent determined by the initial ratio of amine to epoxy groups. The materials were cured either at room temperature or with an additional heat treatment at 150 °C. Structural characterisation of the cured hybrid materials was performed using a combination of Raman, and ²⁹Si and ¹³C MAS NMR spectroscopies. These show that the formation of the two networks does not occur independently and the rate or extent of organic cross-linking has a direct effect on the extent of the inorganic network formation, and vice-versa.     

Oriented inclusions in single crystals of potassium dihydrogen phosphate

Different forms of oriented inclusions in single crystals of potassium dihydrogen phosphate (KDP) grown by gel method and from aqueous solutions are reported. Small rod like chain and channel types of liquid inclusions are illustrated. These inclusions are oriented along 〈001〉, 〈011〉 and 〈010〉 directions and are attributed to mother liquor trapped in the body of the crystal during growth.     

Top-seeded solution growth of LiB3O5

We report on the top-seeded solution growth of LiB₃O₅ from an excess B₂O₃ solution. Parameters investigated include the Li₂O/B₂O₃ ratio, rotation rate, pulling rate, cooling rate, and seed direction. With careful control of the above parameters, we have grown clear crystals of 25 × 30 × 20 mm in size. Selected nonlinear optical properties of these crystals are reported. Observations concerning the occurrence of unstable growth (inclusions, hopper growth) are discussed, and methods to eliminate the unstable growth are suggested.     

The role of hydrodynamics and supersaturation in the formation of liquid inclusions in KDP

The formation of liquid inclusions in large potassium dihydrogen phosphate crystals is a result of depletion in stable eddies formed at the rear (downstream) faces. A large concentration jump can be expected at the point where the “exhausted” fluid meets the fresh liquid. The response of a step train on a jump in supersaturation has been investigated by means of computer simulations. The results are in good agreement with the experiments.     

Mg3N2在生成hBN反应中的催化作用

研究了Mg3N2在B4C和NH4Cl于常压高温下生成hBN反应中的作用,用红外光谱仪和X射线衍射仪对反应产物进行分析,实验结果表明,在950℃和N2气环境下,Mg3N2与B4C反应不成生成hBN,B4C与NH4Cl反应生成少量hBN,在B4C和NH4Cl中加入Mg3N2后hBN的生成量明显增加,说明高温高压下合成cBN的常用催化剂Mg3N2,在常温压高温生成hBN的反应表现催化作用。     

Impacts of growing inclusions on directional crystallization

The destructive influence of internally nucleated growing crystallites upon the growth of an oriented crystal front is examined. In particular, a simple two-dimensional model system is used to study the interaction of an oriented, planar growth front with a particle, initially of negligible size, which grows by circular growth. The locus of the intersection points of the fronts is obtained and used to derive an expression for the misoriented (ruined) area fraction produced by the presence of the growing particle. It is demonstrated that the reduced ruined area fraction is a function of two controlling parameters that describe the relative growth velocity of the interfering particle and its relative nucleation position. The sensitivity of the reduced ruined area fraction to these controlling parameters is ascertained and discussed.     

Formation Volume of Vacancies in Elements and the Defect Formation Mechanism of Melting

The formation volume V_v of vacancies is given by V_v = (h_v/L) ΔV_f with h_v = 8L (formation enthalpy h_v of vacancies and heat L of fusion given in same units; ΔV_f = change of volume due to melting). If there are phase transitions within the solid, L and ΔV_f must be replaced by (L + Δ H_t) and by (ΔV_f + ΔV_t), respectively (Δ H_t and Δ V_t refer to the heat (s) of transition (s) and to the volume change(s) due to transition(s), resp.). The pressure dependence of the melting point is dT_m/dp = (T_mV_v)/h_v. Independent of the sign of V_v any increase of the vacancy concentration above the maximum concentration possible within the solid decreases the melting point thus resulting in the observed surface melting. The melting point is fixed by the characteristics of vacancy formation (h_v, S_v, V_v) and by the bulk modulus of the solid (S_v = formation entropy of vacancies).     

Formation of low density polyethylene/hollow glass microspheres composites

Hydrogen is used to absorb heavy particle radiation, which is the most damaging radiation in space for humans. Low density polyethylene/hollow glass microsphere composites have been suggested as a possible radiation shield because of the high concentration of hydrogen and the low gravimetric density of the microspheres. Composites pressed under 3.90 MPa (566 psi) and 120 °C have the highest probability of success thus far compared to polymers pressed at higher pressures and lower temperatures. Hollow glass microspheres made of borosilicate glasses do not break as easily as hollow glass microspheres made of aluminosilicate glasses. A smooth microsphere surface is better than a rough surface because it distributes the force more evenly, resulting in a more hydrostatic stress environment.     

Migration of liquid inclusions in a solid under asymmetric temperature oscillations

The existence of a new type of thermal migration has been found—the migration of the layer of a liquid phase between two substrates possessing different properties (e.g., two different cuts of a crystal) occurring under the action of asymmetric temperature oscillations. The effect can arise if three following conditions are simultaneously fulfilled: (1) the kinetic properties of the solid-liquid interfaces should be different, (2) the dependence of the growth (dissolution) kinetics on supersaturation should be nonlinear at least at one of the interfaces, and (3) the temperature oscillations should be asymmetric. It is shown that both sign and absolute value of the migration velocity depend on the shape of temperature oscillations. The velocities of migration for liquid layers of various thicknesses as functions of the amplitude of thermal oscillations, their shape, and frequency are calculated for the model Si-Al system.     

Identification of gaseous oxygen and nitrogen in bubble inclusions in Bi4(GeO4)3 (BGO) crystals by means of Raman spectroscopy

Bubble inclusions in BGO crystals have been studied by means of Raman spectoscopy. Since the crystals were grown under ambient atmospheric conditions, we focused our attention on oxygen and nitrogen. Both species are diatomic homonuclear molecules which are vibrationally Raman active. Concerning the vibrational part of the O₂ and N₂ Raman spectra, no evidence was found for the presence of both gases. However, in the spectrum below the lowest 64 cm^-1 energy mode of BGO three faint peaks were found which show the characteristic features of the rotational spectra of O₂ and N₂. It was found that the composition of the inclusion atmosphere was enriched by oxygen compared to the composition of the air.