Low-temperature plasticity and lattice dynamics of solid parahydrogen with an isotopic impurity

The low-temperature plasticity of solid polycrystalline parahydrogen doped with an isotopic impurity (deuterium) is studied. The dependences of the rate of steady-state creep in p-H₂ on the impurity concentration and stress are obtained. The deformation of p-H₂ is described with inclusion of the zero-point mean-square displacements 〈x²〉 of particles making up a crystal. The calculated and experimental values of 〈x²〉 are compared for two possible isotope molecules (HD and D₂) at three stress levels. A correlation between the 〈x²〉 values and an increase in the force constants of a p-H₂ crystal doped with the isotopic impurity is established. An increase in the mean-square displacements of p-H₂ with the tensile load is discussed. Deformation-induced purification of a p-H₂ crystal from the isotopic impurity is suggested to occur.     

Existence of two types of perfect Bi<Subscript>2</Subscript>Sr<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CuO<Subscript>6+δ</Subscript> single crystals

It is found that perfect Bi₂Sr_2?x La _x CuO_6+δ single crystals with the same concentrations of lanthanum x = 0.64 and excess oxygen δ = 0.237 exist in two types. Single crystals of the first type are obtained by slow cooling (the synthesis time is 90–105 h). They have a monoclinic superlattice and exhibit no superconducting transition down to 2 K. Crystals of the second type are obtained by rapid cooling (the synthesis time is 30–40 h) and are characterized by a orthorhombic superlattice and T _c = 18 K. Thus, the superconducting transition temperature is determined not only by the concentration of carriers but also by the configuration of defects. A rhombic superlattice prevails in single crystals obtained by slow cooling in the lanthanum concentration range x = 0.3–0.5, while a monoclinic superlattice dominates in the range x = 0.75–0.85. This fact explains the high values of T _c at optimal doping (x = 0.4) and the absence of high-T _c superconductivity at p < 0.10.     

Effect of electron irradiation on the galvanomagnetic properties of In<Subscript>x</Subscript>Bi<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>3</Subscript> semiconductor single crystals

The effect of 5-MeV electron irradiation of p-In_xBi_2?xTe₃ single crystals (x=0, 0.04, 0.07), performed at 250 K, on the galvanomagnetic properties of the crystals was studied. The irradiation was shown to change the conduction from the p to the n type. Annealing at temperatures of 310–390 K restores the conduction to the p type. The reversal of the conduction type and variation of the carrier concentration can be accounted for by an increase in the concentration of charged point radiation defects produced in In_xBi_2?xTe₃ by irradiation. Electron irradiation of p-type Te single crystals reduces the electrical resistivity without reversing the conduction type. Annealing restores the original properties almost completely.     

Ferromagnetism in a new dilute magnetic semiconductor Sb<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript>x</Subscript>Te<Subscript>3</Subscript>

Magnetic and galvanomagnetic properties of single crystals of a new dilute magnetic semiconductor p-Sb_2?xCr_xTe₃ (x = 0, 0.0115, 0.0215) are investigated in a temperature range of 1.7–300 K. A ferromagnetic phase with a Curie temperature of T_C ≈ 5.8 (x = 0.0215) and 2.0 K (x = 0.0115) is detected. The easy magnetization axis is parallel to the C₃ crystallographic axis. Analysis of the Shubnikov-de Haas effect observed in these crystals in strong magnetic fields leads to the conclusion that the hole concentration decreases as a result of doping with Cr. Negative magnetoresistance and the anomalous Hall effect are observed in Cr-doped samples at liquid helium temperature.     

Anomalous Hall effect and ferromagnetism in the new diluted magnetic semiconductor Sb<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript>x</Subscript>Te<Subscript>3</Subscript>

The magnetic and galvanomagnetic properties of single crystals of the new diluted magnetic semiconductor p-Sb_2?xCr_xTe₃ (0 ≤ x ≤ 0.02) have been studied in the temperature range 1.7–300 K. A ferromagnetic phase with the Curie temperature T_c ≈ 5.8 K and the maximum Cr content x = 0.0215 has been revealed. The easy magnetization axis is parallel to the C₃ crystallographic axis. In the presence of strong magnetic fields, the Shubnikov-de Haas effect has been observed. Analysis of this effect shows that doping with chrome reduces the concentration of holes. Negative magnetoresistance and the anomalous Hall effect are observed at liquid helium temperature.     

Hard antineutrino source based on a lithium blanket: A version for the accelerator target

The β^–-active ⁸Li isotope has a hard and well-defined antineutrino spectrum (E _ν ^max= 13.0 MeV, E _ν= 6.5 MeV) that ensures the reliable detection of the threshold reactions (ν _e, p) and (ν _e, d). An intense ν _e source is proposed within a scheme comprising an accelerator with a neutron-producing target and a lithium blanket. The density analysis of ⁸Li production in this blanket shows that the mass of highly pure ⁷Li can be reduced to 100–200 kg, as compared to ~19.5 t in the option with metallic ⁷Li, and the size of the source can be decreased by a factor of ~2.5, which is important for the proposed short-base experiments on the search for sterile neutrinos.     

Electrical and thermoelectric properties of nanoporous carbon

This paper reports on a study of the temperature dependences of the electrical resistivity, Hall coefficient, and thermopower of nanoporous carbon prepared from polycrystalline carbides (α-SiC, TiC, Mo₂C) and 6H-SiC single crystals in the temperature range 1.5–300 K. The structural units responsible for the character of charge transport in these materials are carbon nanoclusters measuring ～10–30 Å. The conductivity in all the samples studied was found to be p type with a high carrier concentration (n_h ～ 10²⁰ cm^?3). The behavior of the transport coefficients at low temperatures is discussed.     

Electrical instability of LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript> crystals

The temperature behavior of I-U curves and the field and temperature dependences of the electrical resistivity and dielectric permittivity of crystals of the LiCu₂O₂ phase have been studied. It was established that the crystals belong to p-type semiconductors and that their static resistivity in the range 80–260 K follows the Mott law ρ=Aexp(T₀/T)^1/4 describing variable-range hopping over localized states. At comparatively low electric fields, the crystals exhibit threshold switching and characteristic S-shaped I-U curves containing a region of negative differential resistivity. In the critical voltage region, jumps in the conductivity and dielectric permittivity are observed. Possible mechanisms of the disorder and electrical instability in these crystals are discussed.     

Raman spectroscopy of SrB<Subscript>4</Subscript>O<Subscript>7</Subscript> single crystals in the temperature range 300–1273 K

The polarized Raman spectra of SrB₄O₇ (SBO) single crystals are studied in detail in the temperature range of 300–1273 K. The TO, LO, and IO phonon lines of A₁, A₂, B₁, and B₂ symmetries of rhombic SBO at 300 K are identified. The behavior of the Raman spectra of SBO crystals is studied upon heating up to their melting. The relation of Raman spectra with the structure of boron–oxygen fragments, as well as the transformation of spectra in the process of melting of SBO crystals, is discussed.     

C<Subscript>60</Subscript> heat capacity anomaly at the orientational phase transition

An orientational phase transition in C60 crystals was studied by differential scanning calorimetry with the highest resolution provided by this method. The temperature dependence of the specific heat ΔC _p (T) was found to have a double peak in the range 250–270 K. An analysis of the temperature dependences of heat capacity in the region of the peaks revealed that the lower temperature peak follows a power law of the type ΔC _p = A/(T?T₀)^1/2 characteristic of order-disorder second-order phase transitions, while the high-temperature peak can be identified with a diffuse Λ-shaped first-order phase transition.     

Thermoelectric properties and ferromagnetism of diluted magnetic semiconductors Sb<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>3</Subscript>

Thermoelectric properties of single crystals of a new dilute magnetic semiconductor p-Sb_{2 ? x} Cr _x Te₃ are studied in the temperature interval 7–300 K. The temperature dependences of the thermal conductivity are measured. The Seebeck coefficient S is found to increase upon doping with Cr. At low temperatures, a ferromagnetic phase with Curie temperature T _C ≈ 5.8 K exists for a Cr concentration x = 0.0215, its easy magnetization axis being parallel to the crystallographic axis C ₃. At T = 4.2 K, a negative magnetoresistance and anomalous Hall effect are observed; in strong magnetic fields, the Shubnikov-de Haas effect is manifested.     

Pyroelectric properties of some compounds based on protein aminoacids

Protein aminoacid-based compounds were synthesized, and their single crystals were grown. The dielectric and pyroelectric properties of the crystals were studied in the temperature ranges 80–340 and 140–340 K, respectively. It was established that three of the compounds studied (L-His(H₃PO₄)₂, L-TyrHCl, L-Ala₂H₃PO₃ · H₂O) are linear pyroelectrics, with their room-temperature pyroelectric figures of merit being close to those of ferroelectric triglycine sulfate crystals.     

Optical and electrical properties of β-Tl<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>x</Subscript>InS<Subscript>2</Subscript> (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.015) single crystals

The peculiarities of fundamental optical absorption, thermally stimulated conductivity, and depolarization currents in β-Tl_{1 ? x} Cu_xInS₂ (0 ≤ x ≤ 0.015) single crystals have been investigated in the temperature range 4.2–300 K. It is found that the temperature coefficient of the band gap E _g changes near the temperature of the structural phase transition.     

Piezo-optic effect in Cu<Subscript>6</Subscript>PS<Subscript>5</Subscript>Br crystals

The effect of hydrostatic (P=10–400 MPa) and uniaxial σ=0–5.8 MPa) pressures on birefringence Δn of Cu₆PS₅Br single crystals at the wavelength λ=0.6328 μm has been studied below the temperature of the ferroelastic phase transition (T<268 K). It is found that Δn linearly depends on pressure. The obtained data are analyzed.     

Intermediate phases in [111]- and [001]-oriented PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>–29PbTiO<Subscript>3</Subscript> single crystals

Phase transformations in [111]- and [001]-oriented PbMg_1/3Nb_2/3O₃–29PbTiO₃ single crystals have been studied using dielectric and optical measurements before and after applying an electric field. It is shown that the subsequence of phase transitions rhombohedral (R)—tetragonal (T)—cubic (C) phases is observed in nonpolarized samples of both orientations as temperature increases. In the [111]-oriented crystal, an additional intermediate monoclinic phase (it is possible, M _a ) is induced after preliminary polarization at room temperature and the R–M _a –T–C phase transitions are observed on heating. In the [001]-oriented crystal, after its polarization, the monoclinic phase forms instead of the rhombohedral phase even at room temperature and the M _a –T–C transitions occur on heating. The results are discussed from the point of view of the existence polar nanoregions with different local symmetries in a glasslike matrix.     

Heat capacity of the Pb<Subscript>5</Subscript>(Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>)<Subscript>3</Subscript>O<Subscript>11</Subscript> ferroelectric system

The temperature dependences of the molar heat capacity at constant pressure, C_p, of Pb₅(Ge_1?xSi_x)₃O₁₁ crystals with x=0, 0.39, and 0.45 in the range 5–300 K, as well as of their permittivity, dielectric losses, and the pyroelectric effect, have been measured. Experimental data on the temperature behavior of the heat capacity are presented in the form of a sum of two Debye and one Einstein terms, C_p(T)=0.405C_D1(Θ_D1=160 K, T)+0.53C_D2(Θ_D2=750 K, T)+0.046C_E(Θ_E=47 K, T). Besides a peak in the region of the ferroelectric Curie point T_c=450 K for crystals with x=0, the temperature dependences of the heat capacity did not reveal any other pronounced anomalies.     

Effect of chromium and tellurium impurities on the thermoelectric parameters of galena

Concentration dependences of the Seebeck coefficient, resistivity, and thermal conductivity of thermoelectric PbS crystals with chromium (0 < x ≤ 0.01) and tellurium (0 < y ≤ 0.03) impurities are examined in the temperature region of 300–800 K. It is shown that the introduction of chromium increases the number of free electrons in PbCr _x S _1–x crystals and reduces the Seebeck coefficient. However, an increase in the concentration of tellurium in PbCr _x S _1–x–y Te _y alloys raises the Seebeck coefficient while simultaneously reducing the thermal conductivity. As a result, the thermoelectric efficiency of PbCr _x S _1–x–y Te _y crystals increases. The reasons for the observed effects are discussed.     

Isotope shifts of the ground state of neon: Refining the measurement results

Abstract—It has been revealed that the published results of measurements of the isotope shift of the ground state of even neon isotopes contain systematic errors. The errors are caused by the use of erroneous data regarding the absolute values of specific mass shifts of excited states and by the measurement errors of the isotope shifts themselves for transitions to the ground state. The isotope shift of the 2p⁵4s[3/2]₁ → 2p⁶(¹S₀) transition has been measured to be 2305 ± 20 MHz, the absolute specific mass shift of the 3p[3/2]₂: (2_р9) level has been determined to be 647 ± 10 MHz, and the isotope shift of the ground state has been found to be–3156 ± 30 MHz.     

Crystallographic and dynamic characteristics of K<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Rb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiOPO<Subscript>4</Subscript> solid solutions in the low-temperature ranges

The unit cell parameters a and c of K_{1 ? x} Rb _x TiOPO₄ (x= 0, 0.3, and 0.5) crystals are investigated using x-ray diffraction in the temperature range 90–320 K. The thermal expansion coefficients along the principal crystallographic axes of the crystals are determined from the obtained temperature dependences of the unit cell parameters. It is found that the parameter a increases with increasing temperature, while the parameter c decreases. For the crystals under investigation, the elastic moduli c ₁₁ and c ₃₃ along the [100] and [001] directions are determined by the ultrasonic pulse-echo technique in the temperature range 100–350 K. It is shown that c ₃₃ > c ₁₁. The anomalies revealed in the temperature dependences of the crystallographic and dynamic characteristics of the samples at a temperature T ≈ 280 K indicate the occurrence of a phase transition. The temperature of the phase transition is found to increase with increasing rubidium content x.     

Structure,microstructure, and thermopower of highest manganese silicide crystals grown from zinc solution-melt

MnSi_1.71–1.75 single crystals are grown using the combination of solidification from solution-melt and the Bridgman crystal growth technique. The single crystals represent tetrahedral bipyramids and correspond to the highest manganese silicide (HMS) modification with lattice parameters a = b = 5.52(1) Å and c = 65.7(8) Å. The thermopower measured between the parallel faces of these single crystals is anomalously high for plain HMS (180–190 μV/K).