Vol 83, No 6 (2019)

A phase diagram describing the structural, magnetic, transport, and Jahn–Teller properties and their interrelation as a function of the composition and temperature is constructed using the results from measuring elastic moduli, electrical conductivity, and magnetization for lanthanum–strontium manganites of the form La_1 – xSr_xMnO₃ (0.165 ≤ x ≤ 0.18). Local and cooperative Jahn–Teller distortions of the structural MnO₆ octahedra and their effect on the physical properties of materials are studied.

Dependences of Seebeck coefficient S, resistivity ρ, and thermal conductivity κ of narrow-gap PbS_1 –y (0 ≤ y ≤ 10⁻³) semiconductor crystals are studied at a temperature of Т = 305 K. It is found via EPR and the Hall approach that the number of sulfur vacancies and vacancy clusters grows along with nonstoichiometry parameter y of PbS_1 − y samples. Analysis of dependences S(y), ρ(y), and κ(y) shows that the sulfur vacancies and vacancy clusters form resonance levels in the conduction band of the PbS_1 − y crystals that affect their thermoelectric figure of merit.

Explosive dynamic impact on coal samples placed in steel storage ampoules is investigated experimentally. The structural features of coal and the nature of its fragmentation are studied via electron microscopy and laser spectrometry for particle size. The different reaction of coal to the impact was determined, depending on the content of gas (methane) in them and their predisposition to dynamic gas destruction. A high share of particles with sizes of around 0.1 microns is observed in disintegrated samples of coal containing methane and prone to dynamic gas destruction, while particles with sizes on the order of several microns formed a substantial fraction of other coal samples. The main phenomenological difference was that storage ampoules with gas-containing coal were partially destroyed during the tests. The possibility of using the results from coal tests to predict hazardous dynamic gas phenomena in mines is considered.

In situ Raman spectroscopy combined with a resistively heated diamond anvil cell was used to study the behavior of serpentine (chrysotile) Mg₃Si₂O₅(OH)₄ in the presence of NaCl at 100–400°С and 10 kbar. Low H₂O activity leads to a decrease in the dehydration temperature by about 200°C compared to a salt-free system, as well as the formation of only anhydrous products.

An in situ X-ray diffraction (XRD) study of chrysotile Mg₃Si₂O₅(OH)₄ compressed in water under conditions of high Р–Т (up to 8 GPa and 420°С) is performed to clarify the effect an aqueous medium has on the stability of this mineral from the group of serpentine recognized as the most important transporter of water in subduction zones. The transformation of chrysotile to OH-chondrodite Mg₅Si₂O₈(OH)₂ (at 5 GPa and 410–420°С) is observed, along with the onset of decomposition to the 10 Å phase. Compared to a dry system, where chrysotile transitions directly to the 10Å phase, an intermediate phase of OH-chondrodite forms first in a chrysotile–water system.

It is shown that the fcc lattice parameter and the total mean-square displacements of atoms increase when copper is doped with aluminum. Parameters а and с of the hcp α-Ti lattice decrease when titanium is doped with aluminum and vanadium. This effect is attributed to the size factor of radii of alloy elements. The lattice parameter of Ti–6Al–4V alloy samples subjected to electron-beam processing may vary either way compared to α-Ti prior to processing. It is demonstrated that the observed variation of the lattice parameter is induced by the redistribution of aluminum and silicon in surface layers. The mean-square displacement of atoms and the lattice parameters in α-Ti and the Ti–6Al–4V alloy are directly proportional.

The parameters of coordination bonds M ← OH₂ (the magnetic moments of transition metals, interatomic distances, force constants, and break energies) in isostructural nitrilo-tris-methylenephosphonate complexes of transition metals of 3d-series [M^II(H₂O)₃μ–NH(CH₂PO₃H)₃] (M^II = Cr–Zn) are analyzed. It is shown that the correlation of force constants with interatomic distances is in good agreement with the Badger rule, and the break energy of bond M ← OH₂ deviates strongly from the empirical Poling dependence. It is shown that deviations of the break energy of bond M ← OH₂ from the Poling rule are due to the presence of an uncompensated spin density at the central atom. This explains the stability of Fe-containing heterometallic coordination polymers [(Fe,M)(H₂O)₃μ–NH(CH₂PO₃H)₃], which determines the high efficiency of nitrilo-tris-methylenephosphonate complexes as inhibitors of the corrosion of steel in aqueous media.

Correlations of the internal structure (crystalline, grain) and macroresponses (dielectric, ferroelastic, and piezoelectric) in the ferroelectric ceramics of the quasi-binary cross section of the four-component system NaNbO₃–KNbO₃–PbTiO₃–PbZrO₃ are established that allow targeted searches for functional materials for specific applications.

The mechanism of change in the structural, chemical, physicochemical, and technological properties of Lavozero-deposit eudialyte, caused by the effect of high-voltage nanosecond pulses and combined (sequential) electropulse and acid treatment of mineral samples, is studied by means of X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, electrophoretic light scattering (zeta-potential), confocal laser scanning microscopy, microhardness testing, etc. The results show it is possible in principle to use pulsed energy and combined physical and physicochemical effects to improve the effectiveness of disintegration and softening, and to alter the hydrophobicity, sorption activity, and technological properties of eudialyte-group rock-forming minerals.

The block structure of Na_1 – xCa_xNbO₃ (0.0 ≤ x ≤ 0.20) solid solutions formed by the crystallographic shear planes is studied via powder X-ray diffraction. A correlation between the block sizes and the dielectric properties of the samples is established as well.

The dislocation structures and stress–strain curves of Ni single crystals with a [100] compression axis are studied at temperatures of 293 and 673 K. The dislocation structures for both temperatures are shown to arise in the sequence cellular, band, and fragmentary. A rise in temperature has no effect on the type of substructures that are observed in strained Ni single crystals, despite the difference between their parameters.

Transitions in the resistive switching of diode heterostructures based on bismuth selenide, in which bipolar resistive switching is implemented, are investigated. It is found that the time of transitions from one metastable state to another has a fast component on the order of microseconds and a slow component (a shuttle tail). Results are described using the model of a critical electric field, and the parameters of the investigated structures are calculated numerically.

An approach is proposed and used to describe the dependence of surface tension on the composition and temperature of a binary solution without using the traditional approximation of the ratio of coordination numbers on the surface and in the volume of the solution. The values of the surface tension and adsorption of components on different dividing surfaces, and the characteristics of interparticle interactions on the flat surface of an In–Pb liquid solution at T = 643 K are calculated.

The results are presented from an electron microscopic study of the curvature/torsion (χ) of the crystal lattice that occurs upon the deformation of polycrystalline solid FCC solutions. Alloys Cu + 0.4 at % Mn and Cu + 19 at % Mn with mean grain size 〈d〉 = 10–240 μm are investigated. Samples are deformed by tension at room temperature. Causes of curvature/torsion found. It is found that the highest values of χ are characteristic of the joints of grains and grain boundaries.

A comparative analysis is performed of temperature waves passing through matter when initiated by a sinusoidally modulated heat flux and a meandering heat flux. An increase in the thermal conductivity of the material in the dynamic mode is shown to reduce the amount of heat passed through the sample.

Polytherms of the density and surface tension of lead alloys with small additions of sodium in the heating mode from temperatures of melting of Pb–Na alloys up to 650°C in an atmosphere of pure He of grade A (99.995%) are studied using the large sessile drop approach. It is found that the density and surface tension fall as the temperature rises, and raising the content of sodium in the studied alloys to 4 wt % leads to a a substantial drop in surface tension.

The temperature dependence of coercive force H_c(T) of pressed powders of ferromagnetic half metal CrO₂ is compared to the temperature dependence of the maximum field of positive tunneling magnetoresistance H_p(T). It is established that the multidomain alters the nature of the reverse magnetization of transport channels and violates relation H_p ≈ H_c at low temperatures (4.2–70 K).

The linear relationship between surface tension γ_s and radius \(~{{R}_{{\text{s}}}}\) of small particles (nanoparticles) was derived in the 1960s by Rusanov as \({{{\gamma }}_{{\text{s}}}} = K{{R}_{{\text{s}}}},\) where K is the coefficient of proportionality. In this work, a more generalized dependence is obtained in the context of Gibbs’ theory of thermodynamics for curved interfaces on the same size scales for a randomly selected interface, including an equimolecular surface with radius \({{R}_{{\text{e}}}}{\text{.}}\) It is shown that when \({{R}_{0}} \geqslant R \geqslant {\delta }\) (where \({\delta } = {{R}_{{\text{e}}}} - {{R}_{{\text{s}}}},\)\({{R}_{0}}\) is a characteristic radius limiting the range of the Rusanov equation’s applicability), linear dependence \({\gamma } = KR\) should be valid for all \(R \in \left[ {{{R}_{{\text{s}}}},{{R}_{{\text{e}}}}} \right].\) Parameter \(K~\) is estimated for metal nanodroplets and solid metal nanoparticles as well.