Elena Mozhevitina

Homogeneity limits and nonstoichiometry of vapor grown ZnTe and CdTe crystals

The homogeneity regions of zinc telluride ZnTe and cadmium telluride CdTe were studied by the “extraction” technique at 750–1365 K temperature range. It is shown that the homogeneity region of undoped ZnTe contains a stoichiometric composition. The existence of wurtzite-based ZnTe at high temperatures was proven and its lattice parameters were determined. A scheme of the 3C–2H polymorphous transition for ZnTe compounds is proposed in which the transition is followed by peritectic reactions at both the Te-rich and Zn-rich sides. In the case of CdTe, the solidus line near the melting point demonstrated an anomalous behavior, which could be explained in terms of the high-temperature polymorphous transition, but the polymorph was not fixed because of the low transition energy. The undoped ZnTe and CdTe single crystals were obtained by the Markov–Davydov vapor growth technique under pressures close to congruent sublimation conditions in the temperature range 1170–1320 K. The nonstoichiometry and impurity distribution in 60 mm diameter ZnTe and 100 mm diameter CdTe vapor grown crystals were examined.

Purity of MoO3 from different manufacturers

Inductively coupled plasma mass spectrometry with the use of a reaction cell in collision mode has been used to determine the concentrations of 68 elemental impurities in six commercially available molybdenum( VI) oxide reagents. The results indicate that the purity of the reagents is not better than 3N (99.9 wt %). A major impurity in the MoO3 samples is tungsten. Its concentration ranges from 5 × 10–3 to 6 × 10–2 wt %, depending on the manufacturer.

Growth of Li2MoO4 Crystals from Activated Water Solutions

The possibility of obtaining lithium molybdate Li2MoO4 crystals from water solutions activated by low-frequency oscillations of a chemically inert body is examined. It is shown that the activation of the solution increases the equilibrium solubility of Li2MoO4 in the water solution in the temperature interval 25 – 28°C. It is found that the activation of a solution affects the form of the faceting of the crystals grown and the surface morphology of the faces. It is shown that activation of the solution decreases the inclusions of water in the crystals and improves the surface quality of the growing crystal.

Study of the Kroll-process to produce ultra-pure Ti for the low background experiments

To construct G2 & G3 low background experiments for direct Dark Matter search, a lot of ultra-pure construction materials will be needed. Our study of various Ti samples shows that the levels of contaminations of commercially available industrial Ti can varies from 0.2 to 100 mBq/kg for U/Th. It means that the metal Ti is such a promising material for future experiments if the way of production in bulk quantities with very low level of contaminations (below ∼1 mBq/kg of 238U /232Th) would be developed. Our study of the industrial Kroll-process is focused on the possible sources of U and Th and their migration during the multistage Kroll process. To understand migration of U and Th during the Kroll process the set of other impurities available due to precise ICP-MS analysis have been studied. Preliminary results confirm that the Kroll process could be used for the ultra pure Ti sponge production while the following stages of the metal Ti production of from the Ti sponge with necessary mechanical properties...

Deep Tellurium Purification for the Production of Electronic and Photonic Materials

Abstractcarry out the process of obtaining high-purity tellurium by the vacuum distillation method, a reactor design consisting of high-purity quartz glass and graphite is proposed. During the process, the tellurium melt evaporates; and the vapor is transferred from the hot part of the system to the colder one and condenses in the form of a solid phase (distillate) without the formation of a liquid. Regularities in the redistribution of impurities between the distillate and the cube stillage residue, as well as the spatial distribution of impurities in the distillate during the purification of metallic tellurium, are studied. It is established that some impurities, for example, s-metals, Zn, Ni, and V, and rare metals, are distributed uniformly along the length (20 cm) of the distillate. At the same time, Se tends to concentrate in the far (from the still) part of the distillate with a difference of more than one order of magnitude than in the near part.

Selenium solubility in solid zinc selenide

Selenium solubility in solid s-ZnSe (F43m) under mono- and divariant equilibrium conditions has been determined by a direct physicochemical method in the temperature range 850–1173 K. The maximum concentration of excess selenium is 3.76 × 10–4 mol of excess Se per mole of ZnSe at 1173 K. The homogeneity range of the s-ZnSe phase has been shown to be characterized by retrograde solubility at its Se-rich phase boundary. A model has been proposed for defect formation in nonstoichiometric s-ZnSe at temperatures in the range 963–1173 K and pSe2 pressures in the range 1.05 × 10]4 to 5.01 × 105 Pa according to which the dissolution of excess Se is accompanied by the formation of electrically neutral associated vacancy defects in the zinc sublattice.

Spectral properties of powder preparations of cadmium telluride and cadmium selenide with controlled nonstoichiometry

The reflection spectra of powder preparations of cadmium telluride and cadmium selenide with different contents of overstoichiometric components have been investigated in the range of 800–1700 nm. The reflectance is found to be maximum for samples with compositions close to stoichiometric. An increase in the concentration of overstoichiometric cadmium more radically reduces the reflectance in comparison with preparations containing excess chalcogen. It is shown that halftone images in the near-IR range can be formed by using of these materials.

Spectral properties of CdTe-CdSe powders with controlled nonstoichiometry

Chemical compounds based on A^IIB^VI are widely used as phosphors and photosensitive materials for VIS and IR spectral range. It is of common knowledge that functional properties of A^IIB^VI based materials are strongly depended on a deviation from stoichiometry which could be varied within 10^-2 mol.%. At the same time an influence of nonstoichiometry (native point) defects on structure-sensitive properties is no less than that of dopants. Besides phosphors A^IIB^VI powders are applied as inorganic pigments, which color and tint determined both a (CdTe)_x(CdSe)_1-x solid solution composition and a deviation from stoichiometry.