Rapid growth of α-LiIO3 crystal

A fundamental possibility of significantly increasing the growth rate of α-LiIO₃ crystals without the formation of visible defects in them is demonstrated. The corresponding equipment is designed and a technique for obtaining intermediate-size samples is developed. The crystals grown with an average rate of up to 4 mm/days along the Z axis are of high enough quality to be used as materials of optical elements for laser frequency doubling. α-LiIO₃ crystals have been grown both in an open volume via natural faceting and in a rectangular habit, where growth occurs basically through the pyramid (101) face. It is shown that that amount of limiting impurities in the raw material used can be reduced and that the applicability of this material for rapid growth can be verified.     

A brief discussion: Thermodynamic and dynamic fragilities,non-divergent dynamics and the Prigogine–Defay ratio

This article brings together some of the work performed by the present author and collaborators that is related to the glass transition event and to some of its entropy aspects. The purpose of the work and discussion was motivated by a view that some of the frameworks in which we currently look at glassy behavior, while potentially useful, may also have limitations that we often do not fully consider. Discussion focuses on isochoric glass formation paths, thermodynamic and dynamic fragilities and how dynamic fragility in many systems (especially polymers, metals, ionic liquids and hydrogen bonding systems) seems to vary primarily with the glass transition temperature itself. This leads to the conclusion that such systems have an apparent activation energy that varies as the square of the glass temperature. The work then discusses evidence for a non-diverging relaxation time or viscosity as the glass temperature is approached and ends with a discussion of the Prigogine–Defay ratio.     

A brief critique of the Adam–Gibbs entropy model

This paper critically discusses the entropy model proposed by Adam and Gibbs in 1965 for the dramatic temperature dependence of glass-forming liquids’ average relaxation time, which is one of the most influential models during the last four decades. We discuss the Adam–Gibbs model’s theoretical bases as well as its reported experimental model confirmations; in the process of doing this a number of problems with the model are identified.     

Single crystal growth from the melt and magnetic properties of hexaferrites–aluminates

Single crystals of aluminum substituted barium hexaferrite were grown by the floating zone method with optical heating. Single crystals were produced from a melt of stoichiometric composition. The process was carried out under a pressure of 50 atm of oxygen. In the system BaO–(x)Al₂O₃–(6?x)Fe₂O₃ the region of single phase crystal growth from the melt is limited by the value x=3. For higher substitutions single-phase crystallization is not observed. The grown single crystals are cylindrical boules with a diameter of 4–5 mm and with lengths up to 50 mm. To avert cracking the crystals have been annealed during the process of growth at 1100 °C. The content of FeO in the composition of single crystals of barium hexaferrite, grown by zone melting under an oxygen pressure of 50 atm, is approximately 0.3 wt%. In the system of hexaferrite–aluminates the macroscopic magnetic moment of the material disappears at x=3.     

Numerical investigation of the effect of heat shield shape on the oxygen impurity distribution at the crystal–melt interface during the process of Czochralski silicon crystal growth

In this study, a numerical simulation is performed to investigate the effect of the shape of the heat shield on the oxygen concentration in the melt. The results show that the oxygen concentration in the melt can be significantly decreased by increasing the speed of the argon gas near the crucible wall. This can be achieved by enlarging the horizontal length of the heat shield. The oxygen concentration at the melt–crystal interface varies with the length of the crystal growth. In the initial stage, there is a significant decrease in the oxygen concentration as the growth length increases. There is also a significant reduction in the emission of oxygen from the crucible wall due to the lower melt depth and crucible temperature. The transportation of oxygen impurity towards the melt–crystal interface is suppressed by the vortex motion in the melt. When the crystal exceeds a certain length, the oxygen concentration in the melt–crystal interface starts to increase with increasing crystal length, due to the drop in vortex motion in the melt.     

Development of LuAG-based scintillator crystals – A review

A review of research and development of Lu₃Al₅O₁₂ (LuAG)-based single crystal scintillators is presented. Crystals of this type have been prepared by the micro-pulling down method at the initial stage of material screening and by Czochralski or Bridgman methods to obtain higher quality and larger size single crystals afterward. Several different activators, namely Ce³⁺, Pr³⁺, Yb³⁺ and Sc³⁺ have been reported in the literature and such doped LuAG single crystals have been extensively studied to understand a number of issues, including: the scintillation mechanism, underlying energy transfer and trapping processes including the nature and role of material defects involved in the scintillation process and their relation to manufacturing technology. Significant improvements in the understanding of aluminum garnet scintillators lead to the discovery of multicomponent garnet single crystal scintillators in 2011, which are described. These materials gave rise to new class of ultraefficient complex oxide scintillators, the light yield of which considerably exceeds the values achieved for the best Ce-doped orthosilicate scintillators.     

Basic ammonothermal growth of Gallium Nitride – State of the art,challenges, perspectives

Recent progress in ammonothermal technology of bulk GaN growth in basic environment is presented and discussed in this paper. This method enables growth of two-inch in diameter crystals of outstanding structural properties, with radius of curvature above tens of meters and low threading dislocation density of the order of 5?×?10⁴ cm^?2. Crystals with different types of conductivity, n-type with free electron concentration up to 10¹⁹ cm^?3, p-type with free hole concentration of 10¹⁶ cm^?3, and semi-insulating with resistivity exceeding 10¹¹ Ω cm, can be obtained. Ammonothermal GaN of various electrical properties is described in terms of point defects present in the material. Potential applications of high-quality GaN substrates are also briefly shown.     

Bridgman growth of CdxHg1−xTe— A review

Recent developments in the bulk Bridgman growth method for Cd_xHg_1−xTe are reviewed. Both melt mixing and heat flow control techniques have been applied in attempts to produce more uniform material in terms of composition. In the U.K. work has concentrated on application of the Accelerated Crucible Rotation Technique (ACRT) to achieve the required uniformity improvements. Elsewhere, various means to control isotherm shape have been used with the same aim. The ultimate use of the material is in infra-red detectors and Bridgman grown Cd_xHg_1−xTe has produced these successfully for both photoconductive and photovoltaic applications.     

Impact of impurities on the α-LiIO3 crystal growth: Technique for measuring the “dead zone”

Lithium iodate (α-LiIO₃) single crystal is a promising nonlinear optical material, which used for efficient laser radiation conversion in the visible and near-IR regions. A technique for measuring the “dead zone” (ΔТ _dz) of LiIO₃ solutions has been developed; data on the impact of Fe(IO₃)₂, AgIO₃, CsOH, H₃PO₄, and methyl methacrylate on the growth of the (100) face of α-LiIO₃ crystals have been presented; and the dependences of the nucleation and motion of single steps on the degree of supersaturation have been measured. It is shown that the ΔТ _dz value makes it possible to estimate the validity of solutions for growing α-LiIO₃ crystals. The results of measuring the face growth rates and step velocities for KDP and α-LiIO₃ crystals are compared.

     

The crystal and molecular structure of one of the possible conformers of “the smallest piece of ice”—A solid-state isolation of a hydrogen bonded water hexamer trapped within channels of a crystal of a dirhodium molecule

Reexamination of our study of [Rh₂(HNOCCH₃)₄(2H₂O)] 3H₂O (Ahsan, M.Q.; Bernal, I.; Bear, J.L. Inorg. Chem. 1986, 26 260) showed it to be interesting not just because the dirhodium molecule is an antineoplastic but because it contains a hexameric cluster of waters trapped in Rh–Rh lattice cavities. It may well provide an interesting model for the smallest piece of ice (Nauta, K.; Miller, R.E. Science 2000, 287, 293).     

A crystal of a typical EF-hand protein grown under microgravity diffracts X-rays beyond 0.9 Å resolution

We report on our recent observation that crystals of a typical EF-hand protein (parvalbumin or Pa; Ca-loaded component from pike muscle with isoelectric point 4.10) grown under microgravity conditions diffract X-rays to a resolution better than 0.9 Å. The crystals were grown in the US space shuttle and characterized at 100 K, using an X-ray synchrotron beam. An effective atomic resolution has been achieved and substates in the conformation of the protein are observed. Large crystals up to 3 mm were also obtained.     

Phase transformation and crystal growth behaviors of La3+/Ce3+-doped TiO2–20 wt% SnO2 gels

The transformation behaviors of La³⁺/Ce³⁺-doped TiO₂–SnO₂ gels were studied by using differential thermal analysis and X-ray diffraction methods so as to improve the phase transformation and decrease the granularity of crystals. Experimental results show that, anatase, rutile and SnO₂ nanocrystals can exist in the sintering products by varying La³⁺/Ce³⁺ contents and sintering temperatures. 0.8–1.1 wt% of La₂O₃ or CeO₂ doping greatly depresses the growth of anatase and rutile crystals, obtaining nanosized crystals when sintered up to 600 °C for 2 h. With La³⁺/Ce³⁺-doping and increasing their contents, the transformations of gel to anatase and anatase to rutile, as well as the growth of anatase and rutile crystals can be depressed, while the transformation temperature of anatase to rutile receives much less affect. Moreover, the La³⁺-doping has stronger effects on them than Ce³⁺ doping, but has a weaker inhibiting effect on precipitation and growth of SnO₂ crystals.     

A correlation between concentration of deep levels and growth conditions for VPE?GaP

A minimum in deep level concentration in VPE-GaP is found which corresponds to exceptional growth conditions near a relative maximum of the growth rate r in dependence on the GaCl input pressure pG̊aCL. The minimum occurs at the cross-over between mass flow controlled growth (at low pG̊aCL.) and surface reaction controlled growth (at high pG̊aCL.).     

A comparison of the crystal structures of (dabcoH2)CuCl4 and (dabcoH2)CuCl4⋅H2O

The crystal structures of the anhydrous and monohydrated (dabcoH₂)CuCl₄nH₂O salts (n = 0,1) have been determined and a comparison of their crystal structures has been reported. The anhydrous salt is monoclinic P2₁/c with a = 9.045(2) Å, b = 6.9270(10) Å, c = 18.767(4) Å and = 90.07(3)° with V = 1175.8(4) ų. The hydrated salt is also monoclinic P2₁/c with a = 9.266(2) Å, b = 9.395(2) Å, c = 14.386(3) Å and = 93.32(3)° with V = 1250.3(5) ų. The structures of the two salts are closely related. Both compounds contain isolated distorted (compressed) tetrahedral CuCl₄ ^2– anions, diprotonated dabco cations, and in the case of the hydrated salt, lattice H₂O molecules. In the anhydrous salt, each of the two N–H⁺ groups of the dabcoH₂ ²⁺ dications form bifurcated hydrogen bonds to chloride ions on adjacent CuCl₄ ^2– anions along the c axis, thus forming chains running parallel to the c axis. In the hydrated salt, a water molecule is inserted into one of the pair of bifurcated hydrogen bonds, forming instead N–H O–H CuCl₄ ^2– linkages. The chains thus formed are cross-linked by O–H Cl hydrogen bonds between the chains. Because of this additional hydrogen bonding, the CuCl₄ ^2– anions in the hydrated salt are distorted further from tetrahedral geometry.     

Synthesis and crystal structure of a novel tetraiminediphenolate iron(II) macrocyclic complex: A six-coordinate iron–protein model

A novel tetraiminediphenolate iron(II) macrocyclic complex [Fe(tidf)(CH₃OH)₂](NO₃)₂ (1) has been prepared and characterized by microanalysis, X-ray crystallography, FTIR spectroscopy, and mass spectrometry. The crystal structure (monoclinic, space group C2/c, Z=8, a = 26.8573(6) Å, b = 10.6551(4) Å, c = 23.5371(7) Å, = 107.450(2)°) shows that the iron(II) occupies a distorted octahedral geometry with two methanol molecules bound axially. The macrocyclic ligand is very flexible and adopts a butterfly conformation with a dihedral angle of 112°.     

Structural,electrochemical and optical properties of 4′-n-alkyl-4-cyanobiphenyl (nCB) – A computational approach

The structures of nCB (n = 6 & 7 where n is the number of carbon atoms in the alkyl chain) have been optimized using the Becke3-Lee-Yang-Parr (B3LYP) hybrid functional with 6–31G+(d) basis set using the crystallographic geometry as input. The electronic structures of the dimer molecules have been computed using the optimized geometries. The spectra of the dimer molecules have been calculated by employing the DFT method. The features of electronic transitions and excited states have been calculated via configuration interaction singles (CIS) with the semiempirical Hamiltonian Zerner intermediate neglect of differential overlap (ZINDO). The photo sensitivity of liquid crystalline alkyl cyanobiphenyl has been presented on ultraviolet (UV) absorption based approach through Density functional theory (DFT) calculations. The structural and electrochemical properties such as HOMO (H), LUMO (L), and energy gap (Eg = E_L – E_H) have been investigated. A comparison of dimers during the different modes of interactions suggests an absorption maxima at longer wavelength for 7CB, indicating the high photo sensitivity. Further, the 6CB dimers exhibit a lower band gap; hence its conductivity is high in comparison with the 7CB dimers.     

Vibrational spectra,electronic properties and effect of alkyl chain length on chemical stability of nematogens – A comparision using DFT and HF methods

The vibrational spectra of lower homologous series of nematogenic p-n-alkylbenzoic acids (nBAC) with 4 (4BAC) and 5 (5BAC) carbon atoms in the alkyl chain have been investigated using the Density Functional Becke3-Lee-Yang-Parr (B3LYP) level with the basis set 6–31++G(d.p) and Hartree Fock (HF) with the same basis set. The observed vibrational spectra has been resolved and assigned in detail for comparision with both the molecules. These results indicate that DFT and HF values are slightly different at both the level. A comparision of electronic properties such as HOMO (E_HOMO), LUMO (E_LUMO) energies, energy gap (E_g), ionization potential (I), electron affinity (A), electro negativity (χ), chemical hardness (η), electronic chemical potential (μ), electrophilicity index (ω), and softness (S) has been made. It has been observed that decrement occurred in the energy band gap value of isolated molecule with increment in alkyl chain length. This provides valuable information regarding the stability of liquid crystal materials.     

CdWO<Subscript>4</Subscript> crystal growth and production of a spectrometric detection unit with a large-volume (<Emphasis Type="Italic">V</Emphasis> ≅ 350 cm<Superscript>3</Superscript>) crystal

Large-volume (V ≅ 350 cm³) CdWO₄ single crystals of high optical quality have been grown by the Czochralski method. A scintillation detection unit based on a large CdWO₄ crystal has been produced and its characteristics have been studied.     

Phase relations and crystal growth of YBa2Cu3O7−δ in the system YO1.5?BaO?CuO

The liquidus face of the system YBa₂Cu₃O_7−δ BaCuO₂ CuO was investigated by DTA. We found liquidus temperatures below 1000 °C only in a narrow region with small yttrium oxide content near the eutectic of the system BaCuO₂ CuO. The crystallization path of crystal growth experiments is discussed and the principle structure of the phase diagram is derived. Single crystals are grown being superconductive after thermal treatment in oxygen atmosphere.