T. B. Shatalova

Germanium diffusion in lead telluride crystal

Abstract Germanium diffusion in p-type PbTe ( p = 8 × 10 17 −2.6 × 10 18 cm −3 ) was investigated by sputtered neutrals mass-spectrometry (SNMS) and layer-by-layer X-ray analysis at temperatures T = 853–973 K. The problem of optimization of annealing conditions for diffusion study was discussed. From the temperature dependence of the germanium diffusion coefficient ( D Ge ) activation energy was calculated ( E A = 1.4±0.1 eV). It was found that D Ge is proportional to hole concentration. The vacancy mechanism is likely predominant.

Chemical and electrochemical processes in low-temperature superionic hydrogen sulfide sensors

Effect the morphology of the surface of the working electrode (PbS) exerts on the sensitivity of a low-temperature potentiometric hydrogen sulfide sensor is studied. The sensor, which is based on electrochemical cell NaxWO3/NASICON/PbS, may be used for fast selective detection of hydrogen sulfide in air in natural conditions. It is demonstrated that the sensors with PbS that are deposited out of solution have a faster response than the pressed-to ones. The dependence of EMF on the hydrogen sulfide concentration for the former is linear in semilogarithmic coordinates. Thus difference is explained by the microstructure of the lead sulfide layer. It is shown that the lead sulfide interaction with hydrogen sulfide involves a reversible partial reduction of sulfur and lead at the surface. The species that form in so doing contain sulfur atoms in lower oxidation degrees (poly-and oligo sulfides, sulfite). A mechanism of the sensor operation is proposed on the basis of data yielded by experiment and quantum-chemical simulation. The mechanism includes reversible transport of hydrogen from sulfur atoms to oxygen atoms.

Thermally stable, electrically conductive diamond material prepared by high-pressure, high-temperature processing of a graphite + boron carbide mixture

An electrically conductive boron-doped diamond material with high thermal stability and good mechanical properties has been synthesized at high pressures from powder mixtures of graphite and boron carbide. Specific microstructure and high elastic moduli of samples obtained indicate the formation of polycrystalline diamond matrix in the material. The unique combination of physicochemical properties offered by heavily boron-doped diamond can extend its application area as an electrostructural material capable of operating in aggressive media.

Ceramics Based on Brushite Powder Synthesized from Calcium Nitrate and Disodium and Dipotassium Hydrogen Phosphates

Brushite (CaHPO4 · 2H2O) powder has been synthesized in aqueous 1.0 M solutions of calcium nitrate dipotassium hydrogen phosphate, and disodium hydrogen phosphate at a Ca/P ratio of unity, without adjusting the pH of the reaction. After synthesis and drying, the fraction of a reaction by-product (NaNO3, KNO3, or their mixture) in the powder was about 20 wt %. After firing at temperatures from 800 to 1000°C, the ceramics prepared using the powder synthesized from Ca(NO3)2 and Na2HPO4 consisted of β-Ca2P2O7 and β-NaCaPO4. After firing at temperatures from 900 to 1100°C, the ceramics prepared using the powder synthesized from Ca(NO3)2 and K2HPO4 consisted of Са10К(РО4)7 and СаК2Р2О7. The ceramic composites produced in this study can be recommended as materials for resorbable bone implants.

Ge Diffusion in SnTe Crystal

This work is devoted to the study of Ge diffusion in crystalline Sn 1-δ Te 1+8 with δ=0.0065±0.0008 in temperature range T=878-973 K by electron probe microanalysis and layer by layer X-ray analysis. For the latter lattice constant dependence on composition was determined: a (A)= a (SnTe)-(0.368±0.008)× where 0

Ceramics Based on Powder Mixtures Containing Calcium Hydrogen Phosphates and Sodium Salts (Na2CO3, Na4P2O7, and NaPO3)

Ceramic materials in the Na2O–CaO–P2O5 system have been produced using powder mixtures containing calcium hydrogen phosphates (monetite/brushite: CaHPO4/CaHPO4 ∙ 2H2O) and sodium salts (Na2CO3 ∙ H2O, Na4P2O7 ∙ 10H,O, and NaPO3). These salts were used as precursors to the following high-temperature phases: Сa2P2O7, Na2O, Na4P2O7, and NaPO3. The amount of the salts in the powder mixtures was such that the oxide composition of the ceramics corresponded to 10 mol % sodium oxide for each mixture in the Na2O–CaO–P2O5 system. The powder mixtures were prepared using mechanical activation in acetone, which was accompanied by monetite rehydration to brushite. X-ray diffraction characterization showed that, after firing, the phase composition of the ceramics produced from the powder mixtures thus prepared lay in the Сa2P2O7–NaCaPO4–Na2СaP2O7–Са(РО3)2 phase field. The resultant ceramic materials contain biocompatible and bioresorbable phases and can be recommended for bone implant fabrication.

Synthesis of calcium phosphate powder from calcium lactate and ammonium hydrogen phosphate for the fabrication of bioceramics

A calcium phosphate powder has been synthesized from aqueous 0.25, 0.5, and 1.0 M calcium lactate and ammonium hydrogen phosphate solutions atat a Ca/P = 1, without pH adjusting. According to X-ray diffraction data, the as-synthesized powder consisted of brushite (CaHPO4 · 2H2O) and octacalcium phosphate (Ca8(HPO4)2(PO4)4 · 5H2O). After heat treatment in the range 500–700°C, the powders were gray in color because of the destruction of the reaction by-product. The powders heat-treated in the range 500–700°C consisted largely of γ-Ca2P2O7. The ceramics prepared from the synthesized powders by firing at 1100°C consisted of β-Ca2P2O7 and β-Ca3(PO4)2.