I. F. Berger

Phase Diagram and High-Pressure Boundary of Hydrate Formation in the Carbon Dioxide−Water System

Experimental investigation of the phase diagram of the system carbon dioxide-water at pressures up to 2.7 GPa has been carried out in order to explain earlier controversial results on the decomposition curves of the hydrates formed in this system. According to X-ray diffraction data, solid and/or liquid phases of water and CO2 coexist in the system at room temperature within the pressure range from 0.8 to 2.6 GPa; no clathrate hydrates are observed. The results of neutron diffraction experiments involving the samples with different CO2/H2O molar ratios, and the data on the phase diagram of the system carbon dioxide-water show that CO2 hydrate of cubic structure I is the only clathrate phase present in this system under studied P-T conditions. We suppose that in the cubic structure I hydrate of CO2 multiple occupation of the large hydrate cavities with CO2 molecules takes place. At pressure of about 0.8 GPa this hydrate decomposes into components indicating the presence of the upper pressure boundary of the existence of clathrate hydrates in the system.

Structural and Magnetic Properties of Nickel Oxide Nanopowders

Structure and magnetic properties of nickel oxide (NiO) nanopowders have been studied by X-ray/neutron diffraction, SQUID magnetometer, and micro-Raman spectroscopy. Our diffraction data indicate that at room temperature all NiO powders are antiferromagnetically ordered and have a rhombohedral (R-3m) phase. The SQUID magnetometry and Raman spectroscopy measurements support the presence of the antiferromagnetic ordering.

Crystal structure of the low-temperature form of K3PO4

The crystal structure of the low-temperature form of K3PO4 has been determined for the first time using neutron diffraction (Rietveld method) and Raman spectroscopy: orthorhombic cell (sp. gr. Pnma, Z = 4), lattice parameters a = 1.12377(2) nm, b = 0.81046(1) nm, c = 0.59227(1) nm. The structure is made up of isolated [PO4] tetrahedra, with the potassium ions in between.

Real disordered crystal structure and Curie temperature of intermetallic compounds Y2Fe17−xMx (M=Si or Al)

Abstract The crystal structure of intermetallic compounds Y 2 Fe 17 , Y 2 Fe 15.3 Al 1.7 and Y 2 Fe 15.3 Si 1.7 was studied by powder X-ray and neutron diffraction. The real disordered structure of the compounds was found to be a disordered variant of the Th 2 Ni 17 -type structure, in which the Y atoms from the 2b sites substitute in part the Fe “dumbbells” on 4f sites and the Fe atoms occupy part of vacant 4e sites. Besides, the Y atoms implant in 2c sites in the iron plane of the compounds, which causes plane distortions and splitting of the 12j Fe sites into two subsites. The substitution of Fe by Si or Al was found to have a preferential character for sites in the order: 12k, 4f, 4e, 6g and 12j. Partial substitution of Al or Si for Fe is established as resulting in an increase in the atomic Fe–Fe spacing in the 4f “dumbbell” site. The Curie temperature of the compounds Y 2 Fe 17 , Y 2 Fe 15.3 Al 1.7 and Y 2 Fe 15.3 Si 1.7 is proportional to the atomic Fe–Fe spacing in the “dumbbell” site.

Enhanced power factor and high-pressure effects in (Bi,Sb)2(Te,Se)3 thermoelectrics

We investigated the effects of applied high pressure on thermoelectric, electric, structural, and optical properties of single-crystalline thermoelectrics, Bi2Te3, BixSb2−xTe3 (x = 0.4, 0.5, 0.6), and Bi2Te2.73Se0.27 with the high thermoelectric performance. We established that moderate pressure of about 2–4 GPa can greatly enhance the thermoelectric power factor of all of them. X-ray diffraction and Raman studies on Bi2Te3 and Bi0.5Sb1.5Te3 found anomalies at similar pressures, indicating a link between crystal structure deformation and physical properties. We speculate about possible mechanisms of the power factor enhancement and suppose that pressure/stress tuning can be an effective tool for the optimization of the thermoelectric performance.

Composition of cementite in the dependence on the temperature. In situ neutron diffraction study and Ab initio calculations

The structure state of carbon eutectoid steel has been studied by the in situ neutron diffraction method in the temperature range from room temperature to 800°C. It has been shown that an increase in the temperature is accompanied by a decrease in the concentration of carbon in cementite, whereas its weight fraction and the parameters of the orthorhombic lattice change slightly. The ab initio calculations of the nonstoichiometric carbides Fe3Cx (0 < x < 1) indicate that the structure of cementite remains stable upon the appearance of vacancies in the carbon sublattice with a relatively low formation energy. Thus, cementite should be considered as an interstitial phase Fe3Cx with a wide homogeneity range.

Evolution of the microstructure and microdistortions in the austenitic Cr-Ni-Ti steel during aging

Structural mechanism of intermetallic aging of the N26Kh5T3 steel at 600 and 700°C with the precipitation of particles of an ordered γ′ phase Ni3Ti of different sizes has been clarified. Neutron diffraction analysis was used to determine variations in the crystal structure, phase composition, and microdistortions in the samples depending on the aging conditions.

Crystal structure and magnetic properties of a one dimensional complex oxide ca3nimno6

Abstract The results of structural refinements and magnetic properties of one-dimensional oxide Ca 3 NiMnO 6 are presented. The structure of Ca 3 NiMnO 6 was solved by Rietveld analysis of powder neutron date in space group R -3 c with a =9.1227(9) A, c =10.5811(17) A, z=6 (type of K 4 CdCl 6 ). Infinite chains of MnO 6 octahedra and (Ni,Mn)O 6 trigonal prisms sharing faces run parallel to the c axis. The chains are separated by Ca 2+ cations, which are located in a distorted square antiprismatic environment. Magnetic susceptibility obeys the Curie-Weiss law at 300–600 K with μ eff value 5.00 μ B consistent with the valence cationic combination Ni 2+ -Mn 4+ . Magnetic measurements display the antiferromagnetic ordering in Ca 3 NiMnO 6 at 16 K.

Crystal structure of the low-temperature forms of cesium and rubidium orthophosphates

The crystal structure of the low-temperature forms of the Cs3PO4 and Rb3PO4 orthophosphates has been determined for the first time by neutron diffraction using the Rietveld method. Cs3PO4 and Rb3PO4 are shown to be isostructural with K3PO4: orthorhombic cell (sp. gr. Pnma, Z = 4); lattice parameters a = 1.23177(6) nm, b = 0.88948(4) nm, c = 0.64197(3) nm for Cs3PO4; a = 1.17362(2) nm, b = 0.81046(1) nm, c = 0.615167(9) nm for Rb3PO4.

Structure of the intermediate high-pressure phases of ternary lead tellurides

In chambers with diamond anvils, the structure of high-pressure phases of ternary lead tellurides Pb1−xSnxTe (x = 0.29) and Pb1−xMnxTe (x = 0.05) and nonstoichiometric crystals Pb0.55Te0.45, Pb0.45Te0.55 is analyzed by the synchrotron radiation diffraction method at pressures of P up to 14 GPa. The orthorhombic structure of the intermediate high-pressure phase (space group Pnma) is determined for all the samples above 6 GPa. Models of the phase transition in PbTe from the initial rock salt structure to the orthorhombic phase, which constitutes a distorted variant of NaCl, as well as the properties of this phase, are discussed.