Growth of 6Li-enriched LiCl/BaCl2 eutectic as a novel neutron scintillator

In this study, Eu:6LiCl/BaCl2 with a high Li concentration was developed as a novel thermal neutron scintillator. Eu ions were doped as activators for the BaCl2 phase, and Eu:6LiCl/BaCl2 eutectics were grown via the vertical Bridgman–Stockbarger method in quartz ampoules (inner diameter = 4 mm). The Eu:6LiCl/BaCl2 eutectic exhibited a lamellar eutectic structure and optical transparency. The 400-nm emission due to the Eu2+ 4f–5d transition was observed in the BaCl2 phase by a cathode luminescence measurement. The light yield under neutrons was estimated to be over 20,200 photons/MeV. A pulse shape discrimination study was also performed using gamma and alpha-rays. The Eu:6LiCl/BaCl2 eutectic scintillator showed good potential of pulse shape discrimination.

Positron lifetime spectroscopy of defect structures in Cd1–x Zn x Te mixed crystals grown by vertical Bridgman–Stockbarger method

Positron annihilation lifetime spectroscopy was used to examine grown-in defects in Cd1–x Zn x Te mixed crystals as a function of Zn content (x = 0, 0.07, 0.11, 0.49, 0.9, 0.95, 1) and measuring temperature. All samples were prepared using the high-pressure modified vertical Bridgman–Stockbarger method. The crystal structure and material phase were characterized by X-ray diffraction. The positron lifetime spectra reveal the presence of both open volumes and shallow traps regardless of the sample composition. In particular, both average and bulk lifetimes are found to be much higher in ternary alloys (CdZnTe) than those in binary systems (CdTe and ZnTe). This originates from distinct differences in average electron densities and the nature of open-volume defects between binary and ternary samples. Competition in positron trapping with increasing Zn content is observed between defects characteristic for both structural systems. Moreover, a clear correlation is shown between defects and the lattice thermal conductivity of studied samples. The applicability of the positron trapping model to CdTe-based materials is discussed.

Numerical simulation of heat transfer processes during single crystal growth by the Bridgman - Stockbarger method in fixed and rotating crucibles

Численно методом конечных элементов исследованы процессы кристаллизации кремния в плоскодонных неподвижных и равномерно вращающихся графитовых цилиндрических тиглях в режимах сопряженного конвективного теплообмена. Процессы кристаллизации кремния изучены при фиксированной скорости опускания тигля в холодную зону и различных скоростях его вращения. Опускание тигля имитировалось перемещением точки излома в распределении температуры на внешней стороне стенок тигля. Точка излома - это граница перехода от нагретого до начальной температуры участка стенки к области с заданным градиентом температуры. Использованы адаптивные сетки на треугольниках, отслеживающие положение фронта кристаллизации на каждом временном шаге. Использован пакет программ собственной разработки. The dependence of both spatial shape and intensity of the convective flow of silicon melt during the growth of a silicon ingot by the Bridgman-Stockbarger method was studied numerically by the finite element method. Stationary and uniformly rotating graphite crucible in conjugate convective heat transfer regines were examined. The simulation was carried out on the basis of dimensionless system of equations for the thermogravitational convection in the Boussinesq approximation using the bipolar approach. In the mixed convection regine, the system of equations was augmented by an equation for the azimuthal velocity. Adaptive grids on triangles were used to track the position of the crystal-melt interface at each time step. The calculations were carried out at a constant rate of lowering the crucible from the hot to the cold zone, equal to 2.81 cm/h, and at a constant temperature gradient equal to 35 K/cm. Lowering the crucible was simulated by moving the inflection point in the temperature distribution on the outside of the crucible walls. The range of angular velocities of crucible rotation from 0 to 10 rpm is considered. It is shown that as the angular velocity of crucible rotation in the axial region increases, both the velocity of the downward flow arising in the regines of thermogravitational convection gradually and the convective heat flux to the crystal-melt interface decrease. As a result, in the range of angular velocities from 2 to 10 rpm, the shape of the crystal-melt interface gradually approaches to the one typical for the thermal conductivity regime. It is shown that at the initial stage of the process at an angular velocity of 10 rpm in the axial region of the cooled crucible bottom, the nucleation of a single crystal is possible.

Growth and physical properties of CaSrBaF6 single crystals

Using the Bridgman-Stockbarger method, crystals of triple fluoride CaF2-SrF2-BaF2 were grown in a composition range similar to that of CaSrBaF6. The crystals were 10-12 mm in diameter and 50–60 mm in length. The CaSrBaF6 crystal is a new optical material which is transparent in the mid-IR, visible and UV ranges. The uneven distribution of the components along the length of the crystal did not exceed 10 %. The edge of the absorption band in the IR range was 14.3 μm, and the optical absorption at the wavelength of 200 nm did not exceed 18 % (less than 0.2 cm–1). The refraction indices were 1.4527, 1.4488, and 1.4458 for the wavelengths of 633, 969, and 1539 nm respectively. The crystal melts in the temperature range of 1150–1210 °С. The CaSrBaF6 composition is an appropriate matrix for doping with rare-earth ions in order to obtain functional single-crystal and ceramic materials of the visible and IR ranges.

QUASIBINAR SECTION OF AgGaS2-AgSbS2

The aim of this work is to study phase equilibrium and build a state diagram of the AgGaS2-AgSbS2 system. For research, the initial sulfides (AgGaS2 and AgSbS2) were synthesized from elements of high purity in quartz ampoules evacuated to 0.133 Pa. Quaternary alloys of the AgGaS2 – AgSbS2 systems were synthesized from ligatures at a temperature of 800–1300 K, depending on the composition. To homogenize the alloys, annealing was performed at 50–60 K below solidus for 300 h. Using complex methods of physicochemical analysis (differential thermal, X-ray phase, microstructural, microhardness measurement and density determination), phase equilibria in the AgGaS2-AgSbS2 system were studied. It was established that the AgGaS2-AgSbS2 system is a quasibinary section of the eutectic type and its state diagram is constructed. The coordinates of the eutectic correspond to 65 mol. % AgSbS2 and a temperature of 750 K. Based on the starting components in the section, the regions of solid solutions were determined. At room temperature, the regions of solid solutions based on AgGaS2 (8 mol. % AgSbS2) and based on AgSbS2 (14 mol. % AgGaS2) were revealed. At a eutectic temperature, solubility reaches 20 and 25 mol. %, respectively. According to the XRD data, α-solid solutions belong to monoclinic syngony, and with an increase in the concentration of AgGaS2, the lattice parameter increases (a = 12.861-12.972; b = 4.409-4.474; c = 13.282-13.324Å). AgSbS2 triple sulfide solid solutions crystallize in monoclinic syngony. These solid solutions are of the type of substitution. For structural and optical measurements, technological conditions for the growth of crystals of solid solutions were developed and their single crystals were grown. Single crystals of (AgSbS2)1-x(AgGaS2)x solid solutions were obtained by the Bridgman-Stockbarger method.

The Effect of Isovalent Cation Substitution on Mechanical Properties of (CuxAg1–x)7SiS5I Superionic Mixed Single Crystals

(CuxAg1−x)7SiS5I mixed crystals were grown by the Bridgman–Stockbarger method. The microhardness measurements are carried out at room temperature using a Vickers indenter. The compositional dependence of the microhardness is studied. The dependence of the microhardness on the depth of imprint is analyzed in the model of geometrically necessary dislocations. The indentation size effect is observed. It is established that the microhardness of (CuxAg1−x)7SiS5I mixed crystals decreases at the substitution of Cu atoms by Ag atoms.