Магнитные свойства сплавов Pb-=SUB=-1-y-=/SUB=-Sс-=SUB=-y-=/SUB=-Te

The magnetic field dependences of the magnetization (B < 9 Т, T = 2.0 - 70 K) of the samples from a single crystal Pb1-yScyTe (y=0.01) ingot, synthesized by the Bridgman method, are studied. It is established that, in accordance with the generally accepted model of the rearrangement of the electronic structure of alloys during doping, there is no paramagnetic contribution of single scandium ions located in the nodes of the metal sublattice in the studied samples. The magnetization of the samples contains several contributions: superparamagnetism of scandium clusters, linear in field diamagnetism of the crystal lattice and the paramagnetism of free electrons, as well as the oscillating contribution of the de Haas – van Alphen effect. The field dependences of the main contribution of scandium clusters are successfully approximated using the Langevin function. The average concentration, magnetic moment and the total magnetic moment of the clusters per unit volume of the sample were determined with an increase in the impurity concentration along the ingot.

Novel Multicomponent B2-Ordered Aluminides: Compositional Design, Synthesis, Characterization, and Thermal Stability

For the first time, multicomponent alloys belonging to a B2-ordered single phase were designed and fabricated by melting route. The design concept of high entropy alloys is applied to engineering the transition metal sublattice of binary B2 aluminide. The equiatomic substitution of transition metal elements in the Ni sublattice of binary AlNi followed to produce Al(CoNi), Al(FeNi), Al(CoFe), Al(CoFeNi), Al(CoFeMnNi), and Al(CoCuFeMnNi) multicomponent alloys. CALculation of PHAse Diagrams (CALPHAD) approach was used to predict the phases in these alloys. X-ray diffraction and transmission electron microscopy were used to confirm the B2 ordering in the alloys. Thermal stability of the B2 phase in these alloys was demonstrated by prolonged heat treatments at 1373 K and 1073 K up to 200 h.

Ориентационные соотношения при структурном превращении моноклинной и кубической фаз в сульфиде серебра

Based on the experimental data on high-temperature X-ray diffraction and high resolution transmission electron microscopy of silver sulfide, the orientation relationships between the low-temperature monoclinic semiconductor acantite alfa-Ag2S and the high-temperature body-centered argentite beta-Ag2S are determined. It is found that, in contrast to acanthite, the possible distances between silver atoms in a cubic argentite are too small for the positions of the metal sublattice to be occupied by Ag atoms with a probability of 1. It is shown that the acanthite (010) and (001) atomic planes are parallel to the planes ( 1-10) and (221) of argentite, respectively. The orientational relationships found between acanthite and argentite are important for understanding the physical action of the Ag2S/Ag heteronanostructure, considered as a potential basis for creating resistive switches and nonvolatile memory devices.

Эффекты легирования сульфида свинца серебром на решеточных и оптических свойствах твердых растворов Pb-=SUB=-1-x-=/SUB=-Ag-=SUB=-x-=/SUB=-S

Single-phase limited cubic solid solutions Pb1-xAgxS based on PbS with a metal sublattice alloyed with silver are obtained. The maximum relative content of silver in solid solutions Pb1-xAgxS reaches x = 0.15. For the first time the thermal expansion of semiconductor solid solutions Pb1-xAgxS was measured by dilatometry method in the temperature range 295-580 K. Substitution of lead atoms by silver atoms in Pb1-xAgxS leads to a decrease in the coefficient of thermal expansion associated with a change in the anharmonicity of atomic vibrations and a weak increase in the elastic properties. For single-crystal particles PbS and solid solutions Pb1-xAgxS, spatial distributions of the elastic modulus E, Poisson's ratio , and linear compressibility  as a function of the direction (hkl) are found. The reflection spectra of the synthesized powders PbS, Ag2S and Pb1-xAgxS are measured and it is shown that the replacement of lead with silver in PbS is accompanied by an increase in the width of the band gap.

Электронная структура и обменные взаимодействия соединений RNi-=SUB=-4-=/SUB=-Co (R=Eu,Yb)

The electronic structure and the exchange interactions in EuNi_4Co and YbNi_4Co compounds have been calculated in terms of a theoretical approach with the inclusion of electronic correlations (LSDA + U method); the variants of substitution of cobalt ion for nickel in the 3 d lattice in both types of crystallographic positions 2 c and 3 g are considered. The total energies obtained in self-consistent calculations show that individual cobalt impurities are more preferably arranged in position of the 3 g type. A Co ion in RNi_4Co (R = Eu, Yb) is characterized by a significant magnetic moment, which leads to significant increase in the exchange interaction of Co and Ni ions in the 3 d metal sublattice.

Structure of superhard tungsten tetraboride: A missing link between MB2 and MB12 higher borides

Superhard metals are of interest as possible replacements with enhanced properties over the metal carbides commonly used in cutting, drilling, and wear-resistant tooling. Of the superhard metals, the highest boride of tungsten—often referred to as WB4 and sometimes as W1–xB3—is one of the most promising candidates. The structure of this boride, however, has never been fully resolved, despite the fact that it was discovered in 1961—a fact that severely limits our understanding of its structure–property relationships and has generated increasing controversy in the literature. Here, we present a new crystallographic model of this compound based on refinement against time-of-flight neutron diffraction data. Contrary to previous X-ray–only structural refinements, there is strong evidence for the presence of interstitial arrangements of boron atoms and polyhedral bonding. The formation of these polyhedra—slightly distorted boron cuboctahedra—appears to be dependent upon the defective nature of the tungsten-deficient metal sublattice. This previously unidentified structure type has an intermediary relationship between MB2 and MB12 type boride polymorphs. Manipulation of the fractionally occupied metal and boron sites may provide insight for the rational design of new superhard metals.

Improvement of the Thermoelectric Properties of the Chimney–Ladder Compounds in the Ru-Mn-Si System

Directionally solidified alloys in the Ru-Mn-Si system exhibit a particular microstructure including columnar compositional variation due to the formation of many different chimney-ladder phases along the growth direction. Despite the existence of the compositional variation, the crystal orientations of the neighboring chimney-ladder phases are preserved. Over the compositional interfaces, the metal sublattice is considered to be continuous while the Si sublattice is not. Heat treatment of the directionally solidified alloy with the nominal composition of Ru0.10Mn0.90Si1.732 at 1100°C coarsens the compositional domains so as to reduce the density of the compositional interfaces. The values of the thermal conductivity increase with the decrease in the density of the compositional interfaces whereas those of the Seebeck coefficient and electrical resistivity are almost unchanged after the heat treatment. It is considered that the thermoelectric properties of the chimney-ladder compounds in the Ru-Mn-Si system can be enhanced by introducing a high density of the compositional interfaces.