Compositions of melts for growth of functional single crystals of complex oxides and other compounds

The melt compositions (M _c) are calculated for growing crystals with valuable physical properties. The calculation is based on the compositions of the invariant points of the liquidus curves for 33 congruently and 12 incongruently melting solid phases of 42 fusibility diagrams of binary systems. These systems include Na, Ca, Ba, Mg, and Y aluminates; Bi and Pb germanates; Li, K, Ba, and Bi borates; Ba, Fe, Sr, and Bi titanates; Li, K, Cs, Ba, Zn, Ca niobates; Li, Pb, and Gd molibdates; Pb and Nd tungstates; etc. More than 60 studies with data on the experimentally found melt compositions (M _e) for growing the noted crystals are analyzed. It is shown that the melt compositions M _c and M _e for growth of congruently and incongruently melting crystals are similar. Large-size stoichiometric crystals of high optical quality are grown using these melt compositions. Nonstoichiometric crystals of low structural quality are grown from melt compositions either corresponding to the stoichiometric ratio of the components (M _s) or similar to the compositions at invariant points (M _i). In these cases, a large difference is observed between the melt compositions M _c, M _s, and M _e.     

Growth of single crystals of the high-pressure ɛ-FeOOH phase

Single crystals of the high-pressure ?-FeOOH phase are grown from an aqueous solution at p = 7 GPa in the temperature range 580–350°C. Dark brown crystals of prismatic habit are obtained that have characteristic sizes of 0.1 × 0.1 × 0.7 mm. A region of the t-x phase diagram of the H₂O-Fe₂O₃ system at p = 7 GPa is constructed on the basis of the data obtained.     

Kinetic phase diagrams of multicomponent systems

It is derived the method of the calculation of the solidification rate and the concentration of components in the solid phase during the solidification process of the n-component melt at the given undercooling. The calculations are performed in the framework of the stochastic theory of the kinetic phase diagrams, which were derived in the case of the steady-state processes. This is the question of the generalization of relations derived for the binary systems.     

Growth and characterization of CdSe single crystals by modified vertical vapor phase method

Good quality, large single crystals of CdSe were grown by the modified growth method (i.e., vertical unseeded vapor phase growth with multi-step purification of the starting material in the same quartz ampoule without any manual transfer between the steps). Lower temperature gradients (8–9°C/cm) at the growth interface were used for the crystal growth. As-grown CdSe crystals was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive analyzer of X-rays, high-resistance instrument measurement, and etch-pit observation. It is found that there are two cleavage faces of (1 0 0) and (1 1 0) orientations on the crystal, the resistivity is about 10⁸ Ω cm, and the density of etch pits is about 10^3–4/cm². The crystal was cut into wafers and was fabricated into detectors. The detectors were tested using an ²⁴¹Am radiation source. γ-ray spectra at 59.5 keV were obtained. The results demonstrated that the quality of the as-grown crystals was good. The crystals were useful for fabrication of room-temperature-operating nuclear radiation detectors. Therefore, the modified growth technique is a promising, convenient, new method for the growth of high-quality CdSe single crystals.     

Growth of Sb-Bi gradient single crystals

The growth conditions and structural quality of Sb-Bi gradient single crystals with Bi content from 2 to 18 at %, grown by the Czochralski method with solid phase feed, are investigated. Bi distribution in the crystals along their pulling direction are studied by electron probe microanalysis and the change in the interplanar spacing is analyzed by double-crystal X-ray diffraction. It is established that the pulling rate and feed mass affect the Bi distribution in Sb-Bi single crystals.     

Growth of single crystals of quasicrystalline phases

To study the mechanical and physical properties of quasicrystals, single-crystal samples of large size (several centimeters) are necessary. However, obtainment of such single crystals meets a number of difficulties related to the peritectic character of melting of quasicrystalline compounds, high volatility and oxidizability of the initial components, low growth rate in aperiodic directions, and metastability of the most quasicrystalline structures. In this study, criteria for stable growth of quasicrystalline phases have been determined. The growth mechanisms of icosahedral and decahedral single crystals are described and experimental techniques of single-crystal growth are reviewed.     

Growth mechanism of stearic acid single crystals

Micro-morphological observation of the growth patterns on the (001) surfaces of large single crystals of stearic acid grown from solution under moderate growth conditions was carried out by optical and electron microscopy. Two typical growth features, namely, growth spiral steps and two-dimensional (2-D) nucleation-like steps, were identified optically. Then, these patterns were observed in more detail by the replica method of electron microscopy and it was found that the steps are usually two to four times the length of the bimolecular growth unit. These growth units also revealed spiral growth and 2-D nucleation growth patterns.     

Growth of GaSe and GaS single crystals

The paper describes principal manipulations to prepare single crystals of GaSe and GaS. A new simple method of synthesis with single‐zone heating furnace is proposed. Growth of crystals was performed by modified Bridgman method with the use of rotating heat field. Raman and optical depth spectra show high structural and optical quality of obtained crystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and morphology of p-terphenyl single crystals

The results of a preliminary investigation of the growth and morphology of p-terphenyl crystals grown by sublimation and by solvent evaporation methods are reported. It was observed that lozenge–shaped (001) crystal plates are obtained from xylene and benzene solution while dendritic crystals by sublimation. Crystallographic orientation of the plates and microscopic observations of as-grown crystal surfaces are also described.     

Growth and properties of single crystals of FeTi

A Single crystal of FeTi with a diameter of ca 34 mm and a length of ca 48 mm has been grown from a quasi-stoichiometric melt with an excess of 1% titanium employing the Bridgman technique. Experiments with the Czochralski technique were not successful. The only crucible material sufficiently resistent against reaction with the melt is electrographite. Elastic and thermoelastic constants were determined by means of ultrasonic methods. FeTi and α iron possess a similar bulk compressibility, thermal expansion, and thermoelastic constants. The longitudinal elastic resistance c₁₁ of FeTi supersedes that of α iron by an amount of ca 30%.     

Growth and characterization of succinic acid single crystals

Single crystals of ferroelectric succinic acid were grown from aqueous solution by low temperature solution growth technique. The cell parameters and space group are found using powder X‐ray diffraction analysis. The presence of the functional groups has been estimated qualitatively by FTIR analysis. The UV‐Visible spectrum shows the cut‐off wavelength at 240 nm. The thermal stability of the crystal was studied by TG/DTA. The dielectric constant of the crystal studied as a function of frequency shows the pyroelectric property. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of doped-halide single crystals for infrared windows

Single crystals of KCl doped with RbCl have been grown by the Czochralski and Bridgman techniques. Czochralski crystals were grown in air, using platinum crucibles and Bridgman crystals were grown in a Trans-Temp glass furnace in air and also under a reactive atmosphere of CCl₄ in argon. This reactive atmosphere process (RAP) is known to greatly reduce impurities, such as hydroxyl ions, which degrade optical quality. A series of KCl-RbCl-SrCl₂ single crystals have been grown to stabilize microstructure. Some optical absorption and mechanical strength data is presented. An alternative approach to increase halide material strength is to hot-forge a single crystal under temperature and pressure sufficient to cause pressure-induced recrystallization (PIR). Hot-forging techniques to produce high-strength IR windows without degrading optical transmission are given.     

Growth and characteristics of HgGaInS4 single crystals

Single crystals of the HgGaInS₄ layered compound were grown by the iodine transport technique. Results of their optical, photoelectric, and radiative properties' study are presented. The band gap and the binding energy of holes on the sensitizing centres were determined to be E_g = 2.41 eV and E_a = 0.2 eV, respectively. A presence of quasi-continuously distributed states was stated which are responsible for the exponential segment of the absorption edge and which take part in the radiative recombination.     

Growth of NiAl shape memory alloy single crystals

As a potential candidate of high temperature Shape Memory Alloy (SMA), inter metallic compound NiAl has been studied for more than 30 years. In order to understand better the mechanism of the Shape Memory Effect(SME) in β -NiAl phase, its bulk single crystal have been prepared with an improved magnetic levitation cold crucible Czoehralski(CZ) technique in our lab. The crystal growth procedure and the β -NiAl phase stability are discussed in this paper.     

Growth and characterization of mercurous chloride single crystals

Mercurous chloride was purified by repeated sublimation using multichamber distillation column. Single crystals were grown by Physical Vapour Transport technique. During the process of purification of the material, very interesting habit modifications like dendrites and needles were observed. Vickers hardness tests were carried out on the (110) plane of the crystal for different orientations of the indentor. The shape of the impressions for different orientations of the indentor reveals the non-cubic structure of the plane. No structural phase transition in mercurous chloride was observed in calorimetry and optical studies.