Method Of Directed Crystallization Research Articles

INFRARED REFLECTION SPECTRA OF MnxFe1–xIn2S4 SOLID SOLUTIONS

Large-block crystals of FeIn2S4, MnIn2S4 ternary compounds and MnxFe1–xIn2S4 solid solutions are grown by the method of directional crystallization (horizontal Bridgman method). The structure of the obtained crystals is determined by X-ray diffraction analysis. It is shown that both the starting compounds and solid solutions based on them crystallize in the cubic spinel structure. The IR reflection spectra in the frequency range 50–500 cm–1 of crystals of ternary compounds FeIn2S4, MnIn2S4 and solid solutions MnxFe1–xIn2S4 are studied. The frequencies of transverse (ωTO) and longitudinal (ωLO) optical phonons are determined. The concentration dependences of these parameters are plotted and the nature of their behavior is established.

Ordered Submicrometer Structures Developed by Directional Evaporative Crystallization of Acetaminophen in the Presence of Polymers

Crystallization engineering is crucial for the preparation of drug delivery systems with precise release behavior and improved stability. Although evaporation has been commonly used to prepare pharmaceutical film formulations, controlled evaporative crystallization to achieve uniform crystal size and shape has rarely been investigated. In this study, ordered submicrometer composite structures of acetaminophen (ACM) and polymers were prepared via directional evaporative crystallization controlled by a temperature gradient. The ACM crystals had submicrometer sizes while retaining the original crystal polymorph and were aligned along the direction of the temperature gradient, resulting in line structures having branches with uniform and oriented crystal structures. Although the use of a polymer did not affect conventional oven-crystallized films, it significantly decreased the melting point and heat of fusion of directionally crystallized films. The formation of ordered submicrometer composite structures must rely more on kinetic parameters than thermodynamic parameters since no significant intrinsic molecular interactions were discovered. A wide range of sustained-release characteristics could be obtained depending on the polymer types. This unique fast directional crystallization method could offer a new opportunity for future film delivery systems.

INFRARED REFLECTION SPECTRA OF SOLID SOLUTIONS (FeIn2S4)х·(In2S3)1–х

On homogeneous monocrystals of solid solutions (FeIn2S4)х·(In2S3)1–х, grown by the method of directional melt crystallization (vertical Bridgman method), IR reflection spectra in the frequency range of 50—450 cm–1 were studied. The frequencies of transverse (ωTO) and longitudinal (ωLO) optical phonons, as well as their damping coefficients, were determined. The concentration dependences of the mentioned parameters were constructed and the nature of their behavior was established.

Crystal growth and electrical conductivity of Ag7PS6 and Ag8GeS6 argyrodites

Single crystals of ternary argyrodites Ag7PS6 and Ag8GeS6 were grown by the method of directional crystallization from the melt. Large samples with size l = 30 - 40 mm and d = 12 mm were obtained. Grown crystals were investigated by powder XRD, DTA, SEM and EIS methods. The crystal structure of the electron-ionic conductor Ag7PS6 was studied by the Rietveld method. The low-temperature modification of Ag7PS6 crystallizes in a primitive cubic cell SG P213 (No 198) with lattice parameters a = 10.3917 Å and Z = 4. It was established by the SEM method that the studied ternary sulfides Ag7PS6 and Ag8GeS6 are characterized by a defect microstructure. The frequency (1 × 101 – 3 × 105 Hz) and temperature (293–383 K) behavior of electrical conductivity of single crystalline samples were studied. Using the EEC, the contributions of ionic and electronic conductivity were determined and the corresponding activation energies for Ag7PS6 and Ag8GeS6 single crystals were calculated. The influence of structural parameters of Ag7PS6 and Ag8GeS6 on electrical parameters of single crystals is established.

20-21

Crystals of the concentration series ZrO2- (8-10) mol.% Sc2O3- (1-2) mol.% Tb2O3 were grown by the method of directional crystallization of the melt from a cold container. Analysis of the spectral-luminescence characteristics of these crystals after growth and after annealing processing in a vacuum revealed the presence of both Tb3 + and Tb4 + ions in them. In crystals ZrO2- (8-10) mol.% Sc2O3- (1-2) mol.% Tb2O3, the presence of a process of non-radiative energy transfer from Tb4 + ions to Tb3 + ions was revealed.

Спектрально-люминесцентные свойства кристаллов ZrO-=SUB=-2-=/SUB=--Sc-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=--Tb-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

Crystals of the concentration series ZrO2- (8-10) mol.% Sc2O3- (1-2) mol.% Tb2O3 were grown by the method of directional crystallization of the melt from a cold container. Analysis of the spectral-luminescence characteristics of these crystals after growth and after annealing processing in a vacuum revealed the presence of both Tb3 + and Tb4 + ions in them. In crystals ZrO2- (8-10) mol.% Sc2O3- (1-2) mol.% Tb2O3, the presence of a process of non-radiative energy transfer from Tb4 + ions to Tb3 + ions was revealed.

Surface-barrier structures based on solid solutions (In <sub>2 </sub>S <sub>3 </sub>) <sub>х </sub>•(AgIn <sub>5 </sub>S <sub>8 </sub>) <sub>1–х </sub>

Single crystals of solid solutions (In2S3)x⋅ (AgIn5S8)1–x were grown by the method of directional crystallization of the melt (Bridgman method). Studies of the elemental composition and crystal structure of these single crystals have been carried out. On the basis of solid solutions (In2S3)x⋅ (AgIn5S8)1–x, photosensitive structures have been created for the first time and the photoelectric properties of these structures have been determined. The possibility of using the created structures as broadband photoconverters of optical radiation is shown.

Growth of the KR3F10 (R = Tb–Er) Compounds by the Vertical Directional Crystallization Method. II. Refinement of the Character of Melting, Growth, and Some Physical Properties of KDy3F10 Crystals

Growth of the KR3F10 (R = Tb–Er) Compounds by the Vertical Directional Crystallization Method. II. Refinement of the Character of Melting, Growth, and Some Physical Properties of KDy3F10 Crystals

Refinement of the Congruently Melting Composition of Nonstoichiometric Fluorite Crystals Ca1-xYxF2x (x = 0.01–0.14)

The concentration series of nonstoichiometric crystals Ca1–xYxF2+x (x = 0.01–0.14) was obtained from a melt by directional crystallization to refine the composition of the temperature maximum on the melting curves. A precision (±9 × 10−5 Å) determination of lattice parameters of the Ca1–xYxF2+x crystals with the structure of fluorite (sp. gr. Fm-3m) was performed, and a linear equation of their concentration dependence was calculated: a(x) = 5.46385(5) + 0.1999(4) x. The distribution of yttrium along the crystals Ca1–xYxF2+x, the content of which is determined by the precision lattice parameters, is studied. The congruently melting composition x = 0.105(5) of the Ca1–xYxF2+x phase is refined by the method of directional crystallization.

La1–yBayF3–y Solid Solution Crystals as an Effective Solid Electrolyte: Growth and Properties

A series of nonstoichiometric La1–yBayF3–y (0 ≤ y ≤ 0.12) single crystals with a tysonite-type structure (sp. gr. P-3c1) was grown from the melt by the directional crystallization method in a fluorinating atmosphere, and some physical properties were characterized. The concentration dependence of electrical conductivity σdc(y) La1–yBayF3–y crystals was studied. The composition of the ionic conductivity maximum for this solid electrolyte was refined. It was confirmed that the maximum conductivity σmax = 8.5 × 10–5 S/cm (295 K) was observed at the composition ymax = 0.05 ± 0.01. Analysis of the electrophysical data for the group of tysonite-type solid electrolytes R1–yMyF3–y (M = Ca, Sr, Ba, Eu2+ and R = La, Ce, Pr, Nd) showed that the compositions of the maxima of their conductivity were close and amount to y = 0.03−0.05. This fact indicates a weak influence of the size effect (ionic radii R3+ and M2+) on the value of ymax for R1–yMyF3–y solid electrolytes.

Эффективная масса, подвижность носителей заряда и решеточная теплопроводность в нанокомпозитных термоэлектриках на основе халькогенидов висмута и сурьмы

In the p-type thermoelectrics based on bismuth chalcogenides and antimony with an excess bismuth, the density of states effective mass m/m0 increases in nanocomposite and nanostructured solid solutions compared with the base material obtained by the direct crystallization method. It is shown that an increase in m/m0 is associated with an increase in the effective scattering parameter reff and amplifying the relaxation time of energy, which is typical for topological insulators. The material parameter beta, proportional to the thermoelectric efficiency of ZT, at temperatures below room increases stronger in nanostructured composition than in a nanocomposite with the inclusions of SiO2 due to the growth of m/m0 and decrease the lattice thermal conductivity κL. At high temperatures in the range of 300-500 to the greatest growth of the parameter beta in the base material associated with higher mobility.

Optical, electrophysical and structural properties of polycrystalline germanium grown by horizontal directional crystallization method

Optical, electrophysical and structural properties of polycrystalline germanium grown by horizontal directional crystallization method

Horizontal Directed Crystallization: Fabrication and Characterization of High‐Dimension Single‐Crystal Yb:YAG Ingots Grown by Horizontal Directed Crystallization Method (Crystal Research and Technology 12/2020)

Horizontal Directed Crystallization: Fabrication and Characterization of High‐Dimension Single‐Crystal Yb:YAG Ingots Grown by Horizontal Directed Crystallization Method (Crystal Research and Technology 12/2020)

Fabrication and Characterization of High‐Dimension Single‐Crystal Yb:YAG Ingots Grown by Horizontal Directed Crystallization Method

AbstractThe research conducted herein builds upon the achievement of a successful and stable 170 × 300 × 35 mm YAG and 5% Yb:YAG single‐crystals production via the horizontal directed crystallization method. Based on the analysis of residual birefringence pattern in analyzed ingots, a hypothesis is proposed—debating that in certain stages of the growth, {211} facets start to form within some sections of the crystallization front. The sensitivity of the {211} facets to temperature fluctuations seems to cause striations in the facets’ growth sectors. In a later stage of the growth process the slope of the crystallization front naturally changes, which seems to reduce the formation of facets considerably. As a result, the rear part of the crystal achieves the best optical quality. The samples extracted from that portion of the ingot, after annealing, possess good optical quality and heat release of 0.004 1/m at 1070 nm, which is quite low, and is considered a good result for the garnet family of crystals. The lasing experiment with thin‐disk geometry shows a slope efficiency of 52% and proves that the material is suitable for high‐power lasers application.

Growth of Crystals of Fluorite Solid Solutions of the CdF2–PbF2–MnF2 System and Their Spectroscopic Properties

A concentration series of (Pb0.67Cd0.33)1 – xMnxF2 + х (0 ≤ x ≤ 0.7) solid solution crystals and Cd0.93Mn0.07F2 crystal have been grown from melt by the vertical directional melt crystallization (Bridgman) method in a fluorinating atmosphere. Single-phase crystals with the fluorite structure are obtained by doping Pb0.67Cd0.33F2 with manganese fluoride up to 5 mol %. At higher MnF2 contents in the crystals, the tetragonal impurity phase, isostructural to the Ba2MF6 (M = Mn, Co, Zn) group of compounds, is precipitated. The optical absorption and luminescence of the Cd0.93Mn0.07F2 and (Pb0.67Cd0.33)0.95Mn0.05F2 crystals have been investigated. The absorption spectra indicate octahedral symmetry of the environment of Mn2+ ions in the ternary crystal (Pb0.67Cd0.33)0.95Mn0.05F2. The wide Mn2+ luminescence band in (Pb0.67Cd0.33)0.95Mn0.05F2, peaking at 605 nm, is observed only at 77 K.

Mathematical modeling of thermal processes during "cassette" crystallization of chalcogenides

A new, relatively simple and highly efficient modification of the directional melt crystallization method in the form of a multi-cassette process has been considered. This study is based on Russian Patents and technological studies conducted at National Research and Technological University MISiS. As a result, mathematical models of a multi-cassette method have been developed for 3D radiation and conduction analysis of thermal processes in the entire volume of the heating unit and 2D analysis of convection and conduction heat exchange in a separate cassette. Parameters have been calculated on the basis of these mathematical models for clarifying the effect of heating unit component arrangement and dimensions on the formation of thermal fields in cassette units, the effect of vertical homogeneity of heat supply to the cassette unit and heating power reduction rate during crystallization on the shape of the crystallization front, as well as the effect of small asymmetry in cassette design and violation of cassette bottom cooling homogeneity on convection and asymmetrical heat transfer. Application of the conductive and radiative heat exchange model to the entire heating unit has allowed us to calculate process parameters on the basis of which we have analyzed the effect of heating unit components, their arrangement and temperature on the heat exchange conditions at the cassette unit boundaries. Application of the convective and conductive model to one growth cassette has shown that asymmetrical design and boundary thermal conditions as well as unstable vertical temperature gradient lead to the formation of convection vortices and substantial crystallization front deviation from planar shape. Calculations on the basis of the convective mass exchange model have shown that an increase in the crystallization rate by one order of magnitude greatly increases the tellurium flow into the crystal thus substantially altering the melt composition in the vicinity of the crystallization front and hence serving as a potential origin of dendrite growth. The authenticity of the calculation results has been verified in a number of tests aimed at analyzing the effect of heat and mass transport on crystallization front shape for cassette cooling rates that are typical of polycrystalline bismuth telluride growth processes.

Analysis of heat transfer processes for sapphire growth by horizontal directed crystallization method

This research summarizes the analytical and experimental results of heat-transfer processes influence on defects formation during sapphire crystal growth by horizontal directed crystallization method (HDC). The shape of solid-melt interface significantly influences the process of sapphire crystals growth by this method. We receive the Stefan problem solution for sapphire crystals growth. It allows investigating the crystal growth process and the related factors (thermal stresses on different stages of growth process), their influence on defects formation. We investigate the main reasons for the formation of defective structures of the solid phase of sapphire crystals and the influence of thermal unit construction, the crystal geometry on the quality of the resulting sapphire crystal. We study the structure formation process, impurity distribution, and the nature of the defects in the crystal during it growth.

PRODUCTION OF HYIGH-PURITY ZINC SINGLE CRYSTALS BY VERTICAL DIRECTED CRYSTALLIZATION METHOD

A seedless process has been developed to produce high-purity Zn single crystals by the method of vertical di-rected crystallization from a melt. The output of a single crystal structure is from 60 to 80%. Crystals with different growth directions were obtained: [1015] and [0002]. The deviation angles of the growth direction plane relative to the normal to the axis of the sample are 0.5...6°. Microhardness, crystalline perfection of single crystals and micro-structure have been determined. The impurity composition of the start and end parts of single crystals produced from initial grades of zinc of various purities was studied. The developed process can be used to grow single crystals low-melting metals, such as Cd, Pb, Te, In, Bi, Sn, etc.

Mathematical modeling the thermal processes during cassette crystallization of chalcogenides

An original modification of the directed crystallization method is considered as a multi-cassette process, which has comparative simplicity and high productivity. The basis of this research was domestic patents and technological research carried out at the National University of Science and Technology MISIS. As a result, mathematical models of the multi-cassette method were developed that allow both a three-dimensional radiative — conductive analysis of thermal processes in the entire volume of the hot zone and a two-dimensional analysis of convective — conductive heat transfer in a separate cassette. The parametric calculations carried out on their basis were aimed to the identifying an influence of locations and sizes of the hot zone components to a thermal field in the cassette unit; the establishing an influence of vertical heat supply equability to the cassette unit and an influence of heating power decrease during the plate crystallization, as well as to the determining an influence of small cassette design distortions and violation of cooling uniformity in its bottom part on the occurrence of convection and asymmetrical thermal field. By means of the conductive-radiative heat transfer model for the entire hot zone there were carried out parametric calculations and it was analyzed an influence of hot zone components (their locations and temperatures) on the heat exchange conditions at the cassette unit boundaries. By means of the conductive-convective model for a cassette it was determined that the boundary thermal conditions asymmetry, as well as an unstable vertical temperature gradient, result in the convective vortices and a significant deviation of the crystallization front from a flat shape. The calculations with using the convective mass transfer model showed that an increase of the crystallization rate by an order significantly increases a tellurium flux into the crystal, thereby substantially changing a melt composition near crystallization front and, thus, being a potential cause of dendritic growth. The reliability of the calculation results was checked on a number of tests, in which the influence of heat and mass transfer on the crystallization front shape was analyzed at cassette cooling rates corresponding to the growth processes of bismuth telluride polycrystals.

Modelling and numerical analysis of structures made of single-crystal materials

In gas turbine construction, heat-resistant single-crystal materials have taken a strong place. Single-crystal alloy blades are used in aircraft, ships, power plants, etc. Today, the temperature of the blades exceeds the temperature of heat-resistant alloys in normal operating conditions, and they can withstand such high temperatures only with the help of an effective cooling system. In the production of single-crystal blades of a gas turbine engine, the directional crystallization method has been widely used.