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Peculiarities of sintering of foamy ceramic filters based on submicron aluminum oxide powders with additions of titanium oxide and manganese dioxide nanopowders are considered. The processes of removal of polymeric and binder paraffin material during sintering have been studied. The physical and mechanical properties of the obtained porous permeable filters with a foamy structure were analyzed in details. At a sintering temperature in an air atmosphere of 1350 °C, sufficiently high physical and mechanical properties were obtained, which made it possible to use the developed filters as catalyst carriers for vehicle exhaust gases. Bench comparative tests have shown that ceramic filters with a foamed structure are promising catalysts for afterburning car exhaust gases instead of ceramic honeycomb blocks of catalyst carriers. The developed technology allows reducing the sintering temperature of porous foam ceramic filters to 1350 °C and replacing expensive high-temperature ceramic heaters with cheaper nickel-chromium ones. [ABSTRACT FROM AUTHOR]

The influence of irradiation by electrons with energies of 0.5 … 2.5 MeV at temperatures of about 10 K on the basal-plane resistivity of the YBa 2 Cu 3 O 7− δ single crystals is investigated in the range from T c to 300 K. The resistivity temperature dependence is determined by defects arising due to the irradiation. These defects directly affect the superconducting transition, decreasing T c and increasing the transition width without significant distortions of its shape. The resulting defects also lead to an increase in the Debye temperature due to a reduction of the anisotropy, and a noticeable increase in the scattering by phonons in the sample. The excess conductivity does not change with the irradiation used. [ABSTRACT FROM AUTHOR]

We reveal that the temperature dependence of the basal-plane normal-state electrical resistance of optimally doped YBa 2 Cu 3 O 7 − δ single crystals can be with great accuracy approximated within the framework of the model of s-d electron-phonon scattering. This requires taking into account the fluctuation conductivity whose contribution exponentially increases with decreasing temperature and decreases with an increase of oxygen deficiency. Room-temperature annealing improves the sample and, thus, increases the superconducting transition temperature. The temperature of the 2D-3D crossover decreases during annealing. [ABSTRACT FROM AUTHOR]

Temperature dependences of the basal-plane electrical resistance of underdoped YBa 2 Cu 3 O t − δ single crystals are investigated in a broad temperature range down to the superconducting transition, after a fast cooldown from 650 ° C as well as after a room-temperature annealing. A stepped behavior of the superconducting transition has been observed, pointing to an inhomogeneity of the samples. Annealing has been revealed to lead to a narrowing of the superconducting transition and a reduction of both, the residual resistivity and the phonon scattering coefficient. This is accompanied by a slight increase of the Debye temperature attributed to a decrease of the lattice parameter caused, in turn, by a redistribution of the labile oxygen. The revealed changes of the parameters of the temperature dependence of the electrical resistance point to an equalization of the concentration of the labile oxygen in the layers and its ordering. [ABSTRACT FROM AUTHOR]

In the present study, the time dependencies of the resistivity of ReBa 2 Cu 3 O 7 − x (Re=Y, Ho) single crystals with varying degree of deviation from oxygen stoichiometry was investigated. It was shown that the accelerated transport of oxygen ions in the initial stage of the process can be carried out along the one-dimensional non-stoichiometric vacancies’ accumulation by the single file diffusion mechanism. The final phase redistribution of oxygen ions in ReBa 2 Cu 3 O 7 − x (Re = Y, Ho) is described by the classical mechanism of volume diffusion. The substitution of yttrium by holmium significantly affects the charge redistribution and changes the efficient interaction of ions in CuO-planes, thereby modifying the mass transfer diffusion mechanisms in the oxygen sublattice. Thus, a significant length change of the time intervals occurs, corresponding to the oxygen ions’ single file and volume diffusion mechanisms. [ABSTRACT FROM AUTHOR]

The effect of external hydrostatic pressure on the electrical resistance of optimally doped and underdoped YBa 2 Cu 3 O 7 - δ single crystals is investigated in a broad temperature range, which includes the normal state and the region of superconducting fluctuations. The temperature dependences of the resistivity in the normal state are determined by scattering of charge carriers by phonons and defects. The application of pressure leads to significant changes in the electronic structure of the sample and reduces the degree of their defectiveness. This is accompanied by changeû in the lattice characteristics as the sample volume decreases. The fluctuation conductivity only exists within the range of ∼ 0.1 T c . With increasing δ the superconducting characteristics are close to the values typical for conventional low-temperature superconductors. [ABSTRACT FROM AUTHOR]

The understanding of self- and dopant diffusion properties over a range of temperatures and pressures can be technologically important for the formation of defined and efficient nanoelectronic devices. Phosporous, Arsenic and antimony are n -type dopants that can be considered for n -channel germanium metal oxide semiconductor field effect transistors. Using recent experimental data we show that elastic and expansivity data can reproduce the self-diffusion and n -type dopant diffusion coefficient of germanium in the temperature range 702–1177 K. This is achieved in the framework of the cBΩ model, which assumes that the defect Gibbs energy is proportinal to the isothermal bulk modulus and the mean volume per atom. [ABSTRACT FROM AUTHOR]

Measured is the transverse electrical resistance of YBa 2 Cu 3 O 7− δ single crystals with different oxygen deficiency values ( δ ) in the temperature range T c − 300 K. The experimental data are approximated by an empiric expression accounting for the fluctuation conductivity near T c and the semiconductor-like resistance regime. Our analysis of the concentration dependences of the fitting parameters, in particular, reveals that the resistance temperature dependence is largely affected by the sample's non-homogeneity. The latter, in turn, causes a T c anisotropy and variable-range hopping conductivity between different phases. The deduced maximal values of the basal-plane coherence length, ξ xy (0), are comparable with those for low-temperature superconductors. [ABSTRACT FROM AUTHOR]

The effect of high hydrostatic pressure up to 17 kbar on the fluctuation conductivity of lightly Pr-doped Y 1− x Pr x Ba 2 Cu 3 O 7− δ ( x ≈ 0.05) single crystals is investigated. We show that in contrast to non-doped YBa 2 Cu 3 O 7− δ samples, application of a high pressure leads to a substantial increase of the pressure derivative of the coherence length dξ c / dP and a temperature shift of the 2D-3D crossover point. Possible mechanisms of the influence of high pressure on the critical temperature and the coherence length are discussed within the framework of a model assuming the presence of singularities in the charge carriers electron spectrum typical for lattices with strong coupling. [ABSTRACT FROM AUTHOR]

Abstract: The electrical resistivity in the ab-plane of the Y1−y Pr y Ва2Сu3О7−δ single crystals with high degree of perfection in the interval of Т c – 300K was investigated. The increasing of praseodymium content leads to the reduction of the critical temperature (T c ) from 92 to 30K. The experimental results can be approximated by the expression, taking into account the scattering of electrons by phonons, defects, the fluctuation conductivity in the 3D Aslamazov–Larkin model, as well as the transition to a “semiconductor” type behavior of the resistivity at the high praseodymium concentrations. The concentration dependences of all fitting parameters indicate a structural transition in the region 0.35≤у≤0.43. In particular, the Debye temperature changes in this range from 350 to 550K, and the transverse coherence length passes through a maximum ξ С (0)≈5Å. The concentration dependence of the critical temperature testifies the d-pairing of the BCS model. [Copyright &y& Elsevier]

Abstract: We investigate the conducting properties in the basal ab-plane before and after a long time exposure in air atmosphere of the optimally oxygen doped YBa2Cu3O7−δ single crystals. Prolonged exposure leads to an increase of the effective scattering centers of the normal carriers. The excess conductivity in a wide temperature range has exponential temperature dependence and near the critical temperature is well described within the Aslamazov–Larkin theoretical model. The prolonged exposure increases to a great extent the temperature range of the implementation of the pseudogap state, narrowing the linear section of the temperature dependence of the resistivity in the ab-plane, ρ ab(Т). [Copyright &y& Elsevier]

Abstract: We investigate the influence of the disorientation angle between the direction of a constant magnetic field (up to 15kOe) and the ab-plane α ≡∠(H,ab) to the temperature dependence of the excess conductivity in the temperature interval of the transition to the superconducting state in untwinned YBa2Cu3O7−δ single crystals. We discuss the appearance of low temperature “tails” (para-coherent transitions) on the resistive transitions, corresponding to different phase regimes of the vortex-matter state. At temperatures above the critical temperature, the temperature dependence of the excess para-conductivity is interpreted within the Hikami–Larkin theoretical model of the fluctuation conductivity for layered superconductors. [Copyright &y& Elsevier]

Abstract: Perovskites and related oxides are a very important class of functional materials that exhibit a range of stoichiometries and crystal structures. The oxygen diffusion mechanisms and activation energies in these materials are highly influenced by the composition, stoichiometry and crystal structure. We review the significance of a range perovskite related oxides but focus on two characteristic materials: La2NiO4+δ and LnBa2Cu3O7−δ (where Ln =rare-earth cations). La2NiO4+δ is considered as a cathode material for solid-oxide fuel cells, whereas LnBa2Cu3O7−δ is the archetypal superconducting oxides. [Copyright &y& Elsevier]

Abstract: The effect of annealing at room temperatures on the conductivity in the basis plane of oxygen deficient HoВа2Сu3О7− δ single crystals, tempered from a temperature of 650°C is investigated. We determine that during the annealing process an extension of the area of the linear dependence of the resistivity ρab (T) occurs. A shift downwards of the temperature interval corresponding to the metal-to-insulator transition and a considerable transformation of the form of the resistivity transfers to the superconducting state was observed. The absolute value of the temperature that the pseudo-gap regime commences is reduced by about 20K. The results are attributed to labile oxygen ordering without changing the concentration of oxygen in the sample. The estimation of the cluster sizes is characterized by the differences in oxygen content. We perform a comparative analysis between the experimental data with the predictions of the high temperature superconductivity cluster theory. [Copyright &y& Elsevier]

Abstract: The temperature dependence of the transport anisotropy of ReBa2Cu3O7−δ (Re=Y, Ho) single crystals is investigated. We experimentally determine the parallel and perpendicular conductivity in oxygen deficient single crystals. It is found that, in these single crystals, oxygen deficiency results to uneven oxygen distribution within their volume that leads to the formation of superconducting phases with different critical temperatures. We present an analysis regarding the agreement of the experimental data with the predictions of different theoretical models. It is determined that, the absolute values of the energy gaps along and perpendicular to the basis plane are changed, with different signs of their derivatives. When the value of Δ c increases, the value of the pseudo-gap decreases and vice versa, testifying that the PG regime is suppressed, with a synchronous strengthening of the localization effects. In distinction to YBa2Cu3O7−δ , the temperature dependence of the anisotropy of the resistivity ρ c /ρ ab (T) for the HoBa2Cu3O7−δ samples is well described, by the universal “law of 1/2” for the thermally activated hopping conductivity. [Copyright &y& Elsevier]

Abstract: The influence of hydrostatic pressure of up to 11kbar on the fluctuation conductivity in the ab plane of the YBa2Cu3O7−δ (YBCO) single crystals with various oxygen concentrations is studied. In contrast to samples of stoichiometric composition, the application of high pressure on samples with oxygen deficiency, leads to the decrease of the coherence length perpendicular to the ab plane ξ c(0). The pressure-induced redistribution of the labile oxygen causes a shift of the temperature interval in which three-dimensional superconducting fluctuations exist and a diffusion redistribution of the labile components from the phase of lower critical temperature to the high-temperature superconducting phase. [Copyright &y& Elsevier]

The understanding of oxygen self-diffusion over a range of temperatures is important in UO 2 and ThO 2 particularly for nuclear fuel applications. A way to realize this is by the cBΩ model in which the defect Gibbs energy is proportional to the isothermal bulk modulus (B) and the mean volume per atom (Ω). In the present study elastic and expansivity data is used in the framework of the cBΩ model to derive the oxygen self-diffusion coefficient in UO 2 and ThO 2 in the temperature range of 2000 K to 3000 K. The derived results are in excellent agreement with the most recent experimental and theoretical data. [ABSTRACT FROM AUTHOR]

Abstract: The electrical resistance in the range of Т C–300K in the layer planes of YВа2Сu3О7−δ single crystals with a range of oxygen deficiency (providing a range of T C from 78 to 92K) was investigated. The experimental data is approximated by an expression that accounts for the scattering of electrons on phonons, as well as on defects and the fluctuation conductivity in a 3-D model of the Aslamazov-Larkin theory. According to this approximation, depending upon the oxygen deficiency, the Debye temperature varies from 245 to 400K, coherence length ξ С(0)≈0.5Å. [Copyright &y& Elsevier]

Abstract: In the present work the effect of hydrostatic pressure up to 10kbar on in-plane electrical resistivity of well-structured YBa2Cu3O7−δ (δ<0.15, Т с≈91K, ΔТ с≈0.3K) single crystals was investigated. The influence of the twin boundaries on the electrical resistivity was minimized. The resistivities temperature dependences in the interval Т с up to 300K can be approximated by taking into account the linear term at high temperatures and the fluctuation conductivity (Maki–Thompson model) near Т с. The parameters of the linear dependence of R(T) are decreasing as the pressure is increasing. Т с increases linearly when the pressure increases with the derivative dT c /dP≈0.080K/kbar. Among the Maki–Thompson model parameters the inter-layer distance, d, can be considered to be independent from pressure, the transverse coherence length, ξ c (0)∼0.1d. [Copyright &y& Elsevier]

Abstract: We investigate the influence of praseodymium content on the basis plane conductivity of Y1− х Pr х Ba2Cu3O7− δ single crystals. An increase of the praseodymium concentration leads to the enhancement of the localization effects and the appearance of a metal–insulator transition in the system, which always precedes the superconducting transition. The increase of the concentration of praseodymium, leads to a significant displacement of the point of the metal–insulator transition in the low temperature region. [Copyright &y& Elsevier]

Abstract: We investigate the relaxation of the normal electrical resistivity, induced by high-pressure in YBa2Cu3O6.45 single crystals. It is determined that the pressure affects to the phase composition of the sample. Under pressure phases with different (but similar) critical temperatures form. It is determined that the application-removal pressure process is completely reversible. Above T c the temperature dependence of the resistivity in the layers'' plane at different hydrostatic pressures can be approximated with high accuracy with the scattering of electrons by phonons model. With increasing pressure, the residual resistance is reduced and the contribution of intraband s–s scattering increases. Additionally, the role of the interband s–d scattering and the Debye temperature is enhanced. [Copyright &y& Elsevier]

Abstract: We have investigated the conductivity in the basis plane of YBaCuO single crystals slightly doped by Al and Pr with a pre-specified topology of twin boundaries. The excess conductivity for the analyzed samples shows dependence in a wide temperature range , where is the mean field temperature of superconducting transition. The temperature dependence of the pseudogap can be satisfactorily described in terms of the BCS–BEC crossover theoretical model. [Copyright &y& Elsevier]

Evolution of the excess conductivity in YBCO single crystals is investigated after their step-by-step irradiation with fast electrons. The dependence of the coherence length ξ c (0) along the c -axis on the irradiation dose dependence is obtained. It is revealed that an increase of the irradiation dose from 1.4 to 8.8 × 1018 cm − 2 leads to a considerable extension of the temperature range of the excess conductivity. This is accompanied by a factor of about 1.5 increase of ξ c (0) and a shift ot the 2D-3D crossover point in temperature. [ABSTRACT FROM AUTHOR]

• YBCO single crystals are irradiated with fast electrons and annealed in oxygen atmosphere. • The irradiation and annealing lead to a broadening of the superconducting transition. • Resistivity temperature dependence is described by a combination of different conductivity mechanisms. • Annealing allows one to recover the normal conducting properties to the initial, non-irradiated state. The effect of annealing on the conductivity of optimally doped YBa 2 Cu 3 O 7 − δ single crystals irradiated with fast electrons is investigated. The variation of width of the superconducting transition with increase of the irradiation dose and in the course of annealing is associated with the evolution of the sample inhomogeneity. A recovery of the critical temperature T c after annealing to some intermediate value between those in the initial and irradiated states is observed. This recovery of T c is accompanied by a substantial narrowing of the superconducting transition whose width nicely matches that in the non-irradiated state. The observed transition narrowing is attributed to an improvement of the sample homogeneity in consequence of the diffusion-induced growth and eventual coalescence of superconducting domains. In addition, the complete recovery of the normal conductivity after annealing points to a reversible change of parameters of the charge carriers scattering on phonons and defects. [ABSTRACT FROM AUTHOR]

It has been determined that carbon-oxygen-self-interstitial defects in silicon (Si) can influence the operation of devices through the concentration of intrinsic point defects. Doping with larger isovalent dopants such as germanium (Ge) and tin (Sn) can impact the formation, energetics and structure of defect clusters in Si. In the present study we use density functional theory calculations to gain insights on the formation and stability of the C i O i (Si I ) n (n = 0, 1, 2) defects in Si doped with Ge or Sn. It is calculated that the C i O i (Si I ) n defects will preferentially form away from the oversized dopants. This result for the interstitial clusters is opposite to what is expected for vacancy-containing clusters which strongly associate with oversized dopants. [ABSTRACT FROM AUTHOR]

The influence of the hydrostatic pressure P up to 0.95 GPa on the excess conductivity σ ′( T ) and the pseudogap Δ ∗ ( T ) in optimally doped YBa 2 Cu 3 O 7− δ single crystals ( T c ≃ 91.1 K at ambient pressure) is investigated by electrical resistivity measurements. A pronounced enhancement of the pseudogap under pressure of d lnΔ ∗ / dP ≈ 0.32, which is only a factor of 1.12 smaller than in slightly doped single crystals, is revealed for the first time. This implies a somewhat more moderate increase of the coupling strength in optimally doped cuprates with increasing pressure. Simultaneously, the ratio 2Δ ∗ ( T c )/ k B T c ≈ 5 at P = 0 GPa, which is typical for high-temperature superconductors with strong coupling, increases by 16% with increasing pressure. At the same time, the pressure effect on T c is minor: dT c / dP ≈ +0.73 K GPa −1 , whereas d ln ρ / dP ≈ (−17 ± 0.2)% GPa −1 is comparable with that in lightly doped YBCO single crystals. This suggests that the mechanisms of the pressure effect on ρ ( T ) and T c are noticeably different. Independently of pressure, near T c , σ ′( T ) is well described by the Aslamazov-Larkin (3D-AL) and 2D Hikami-Larkin fluctuation theories, exhibiting a 3D–2D crossover with increasing temperature. However, the temperature interval T c < T < T 01 , in which σ ′( T ) obeys the classical fluctuation theories, is exceptionally narrow (≈1.16 K). Nevertheless, a peculiarity at the temperature T 01 , up to which the wave function phase stiffness in the superconductor is maintained, is clearly observed in the dependence Δ ∗ ( T ). Below T 01 a fast growth of Δ ∗ ( T ) is revealed for the first time. It can be associated with a sudden increase of the superfluid density, n s , that is the density of fluctuating Cooper pairs (short-range phase correlations) forming in the sample when T approaches T c . [ABSTRACT FROM AUTHOR]

The influence of hydrostatic pressure P up to 1.05 GPa on resistivity ρ , excess conductivity σ ′ ( T ) and pseudogap Δ ⁎ ( T ) is investigated in slightly doped single crystals of YBa 2 Cu 3 O 7− δ ( T c ( P = 0 ) ≈ 49.2 K and δ ≈ 0.5 ). The critical temperature T c is found to increase with increasing pressure at a rate dT c / dP =+ 5.1 KGPa − 1 , while ρ ( 300 K ) decreases at a rate d ln ρ / dP = ( − 19 ± 0.2 ) % GPa − 1 . Near T c , independently on pressure, σ ′ ( T ) is well described by the Aslamasov–Larkin and Hikami–Larkin fluctuation theories, demonstrating a 3D–2D crossover with increase of temperature. The crossover temperature T 0 determines the coherence length along the c -axis ξ c ( 0 ) ≃ ( 3.43 ± 0.01 ) A ˚ at P =0, which is found to decrease with increasing P . At the same time, Δ ⁎ and the BCS ratio 2 Δ ⁎ / k B T c both increase with increasing hydrostatic pressure at a rate d ln Δ ⁎ / dP ≈ 0.36 GPa − 1 , implying an increase of the coupling strength with increasing P . At low temperatures below T pair , the shape of the Δ ⁎ ( T ) curve is found to be almost independent of pressure. At high temperatures, the shape of the Δ ⁎ ( T ) curve changes noticeably with increasing P , suggesting a strong influence of pressure on the lattice dynamics. This unusual behavior is observed for the first time. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the conductivity in the basis plane of the non-stoichiometric ReBa2Cu3O7−δ (Re=Y, Ho) single crystals. The excess conductivity (Δσ) is described by in the wide temperature range T f < T < T*, where T* is the mean field temperature of the superconducting transition. We determined that the temperature dependence of the pseudogap (PG) is described in terms of the BCS–BEC crossover theoretical model. It is observed that a reduction in the oxygen content leads to the widening of the temperature interval, in which the PG region is realized, and to the narrowing of the area of the ρ(T) linear dependence in the ab-plane. [Copyright &y& Elsevier]

Highlights: [•] The substitution of Y by Ho significantly affects the charge distribution. [•] The disordering in the oxygen subsystem which is affected by pressure. [•] Twin boundaries are effective scattering centers of normal carriers. [•] Near the conductivity is described by the Aslamasov–Larkin theory. [•] demonstrates two representative maxima which disappear under pressure. [ABSTRACT FROM AUTHOR]

Investigates the effect of low-temperature annealing on the superconducting transition temperature and electrical resistance of single crystals of YBa(sub 2)Cu(sub 3)O(sub 7-sigma) quenched from temperatures of 620-650 degrees Celsius. Increase in transition temperature and decrease in resistance during annealing; Isothermal relaxation of resistance.

The temperature dependence of electrical resistivity in the temperature range from 4.4 to 300 K for Ti 41 Zr 41 Ni 18 (at.%) thin coatings of various crystal perfection and phase compositions has been investigated. The films were deposited by the magnetron sputtering method. The following vacuum annealing in various modes provided several combinations of the film phases such as 1/1 and 2/1 crystal-approximant phases, the quasicrystalline icosahedral phase, Laves (Ti,Zr) 2 Ni phase and α-Ti(Zr) solid solution phase. The structure and composition of the films before and after annealing were studied in detail by X-ray diffractometry and cross-sectional high-resolution transmission electron microscopy. Samples with predominant amorphous, quasi-crystalline, and approximant 2/1 phases have a temperature coefficient of resistance less than zero, while samples dominated by crystalline phases exhibit the characteristic metallic conductivity. For the quasicrystalline Ti 41 Zr 41 Ni 18 film, the temperature dependence of the electrical resistance turned out to be similar to that of bulk samples with the composition Ti 40 Zr 40 Ni 20. A significant effect of the presence of phases with metallic conduction on the overall conductivity of the coating is described. The electrical resistance of the 2/1 approximant phase with a low content of the additional Laves phase in the film has an almost constant value over the entire temperature range under study. • Ti 41 Zr 41 Ni 18 alloy films with various structural phases were obtained by heat treatment. • Films consisting of amorphous, quasicrystalline, 2/1 approximant, solid solution, Laves phases were studied. • Drastically different behavior of temperature dependences of the electrical resistance was observed for various phases. • The 2/1 approximant phase with a small content of the Laves phase has an almost constant resistance from 4.4 to 300 K. [ABSTRACT FROM AUTHOR]

In this study, density functional theory (DFT) calculations were performed to investigate the key structural, elastic, mechanical, thermal, and electronic properties of the MAX phases of Zr 2 AlC and Nb 2 AlC, and particularly their solid solutions (Zr 1- x Nb x) 2 AlC, which are found to be thermodynamically stable. The partial inclusion of Nb in the M-site improves the bond strength and the hardness of Zr 2 AlC. The stiffness of (Zr 1- x Nb x) 2 AlC increases with the Nb-content x , and thus improves its ability to resist the shear deformation. With large negative Cauchy pressure, all of the compositions of (Zr 1- x Nb x) 2 AlC are predicted to exhibit directional covalent bonding. The composition with x = 0.2 is expected to be more brittle than the other compositions. The other properties including the anisotropy in elasticity, average sound velocity, Debye temperature (predicted to be highest for the composition with x = 0.4 in (Zr 1. x Nb x) 2 AlC), melting point, electronic structures, and Vickers hardness were examined. The covalency increases in (Zr 1- x Nb x) 2 AlC as the Nb-content x increases, which may explain the increase in the stiffness of the compositions. Image 1 • (Zr 1- x Nb x) 2 AlC are thermodynamically stable. • Elastic moduli of (Zr 1- x Nb x) 2 AlC increase with Nb content x. • (Zr 0.6 Nb 0.4) 2 AlC composition predicted to be highly thermally conductive. • Covalency in (Zr 1- x Nb x) 2 AlC increases with Nb-content x. [ABSTRACT FROM AUTHOR]

Abstract Lithium metatitanate, Li 2 TiO 3 , is a material that is being considered for the breeder blanket region of fusion reactors, and as a cathode material in lithium batteries. We employ atomistic simulations to study the point defect processes and lithium diffusion in Li 2 TiO 3. It is calculated that the activation energy of migration of Li ions via the vacancy mechanism is 0.51 eV along the ab plane. The energetically favorable intrinsic defect type is Li Frenkel (1.25 eV/defect). This is important as the formation of Li vacancies is required as they act as vehicles for Li diffusion in the vacancy mechanism. The solution of trivalent dopants can contribute further Li vacancies, however, the synthesis routes should be determined experimentally. Highlights • Atomic scale simulations based on classical pair potentials have been employed to study the point defect processes and lithium diffusion in Li 2 TiO 3. • The energetically favourable intrinsic defect type is Li Frenkel (1.25 eV/defect). • It is calculated that the activation energy of migration of Li ions via the vacancy mechanism is 0.51 eV along the ab plane. • Subvalent doping by Al on the Ti site is calculated to be an energetically favourable process and an efficient way to increase the Li content in Li 2 TiO 3. [ABSTRACT FROM AUTHOR]

The elastic behavior and thermodynamic properties of recently synthesized (Zr 3− x Ti x )AlC 2 MAX phases are investigated for the first time using density functional theory and the quasi-harmonic model. The unit cell properties and elastic tensors are evaluated and the total energy is utilized to calculate the equation of state along with free energy in the scheme of the phonon-based quasi-harmonic model. The consistency between the theoretical and experimental lattice parameters is very good, with the lattice constants a and c decreasing significantly with the increase of Ti content x in (Zr 3− x Ti x )AlC 2 . The mechanical stability of the (Zr 3− x Ti x )AlC 2 MAX phase solid solutions is verified. The increase of Ti content x , increases the stiffness of (Zr 3− x Ti x )AlC 2 . The solid solutions (Zr 3− x Ti x )AlC 2 should be brittle in nature. The thermodynamic properties such as the thermal expansion coefficient α , Debye temperature θ D , bulk modulus B , heat capacities C p and C v , entropy S , Grüneisen parameter γ , and normalized volume V / V 0 are calculated at temperatures from 0 to 1000 K and pressures from 0 to 50 GPa, respectively. We expect that the calculated elastic and thermodynamic data can provide an essential reference as some of the physical properties can be difficult to be experimentally determined for a wide composition range. [ABSTRACT FROM AUTHOR]

The effect of hydrostatic pressure up to 12 kbar on electrical resistance in the basal ab-plane of optimally oxygen-doped Y 1– x Pr x Ba 2 Cu 3 O 7–δ single crystals doped with praseodymium (х ≈0.23) has been investigated. It was determined that the introduction of praseodymium leads to a fivefold increase in the baric derivative dT c / dP at zero pressure; however, as the pressure rises, dT c / dP decreases to a level characteristic of undoped Y 1– x Pr x Ba 2 Cu 3 O 7–δ samples with an optimal oxygen content. • hydrostatic pressure does not affect the morphology of a superconducting cluster in Y 1- x Pr x Ba 2 Cu 3 O 7-δ. • Pr leads to a fivefold increase in the baric derivative dT c / dP at zero pressure. • As pressure rises, dT c / dP decreases to a level characteristic of undoped Y 1– x Pr x Ba 2 Cu 3 O 7–δ. [ABSTRACT FROM AUTHOR]

A systematic density functional theory study with two functionals –generalized gradient approximation (GGA) and local density approximation (LDA)–is carried out to explore the structural, electronic, elastic, thermal, vibrational and optical properties of a new 211 MAX phase Nb 2 CuC. To facilitate comparison we also study Nb 2 AlC, the precursor of Nb 2 CuC. The calculated band structures reveal the metallic conductivity of both compounds. The replacement of Al with Cu modifies the band profiles of Nb 2 CuC and consequently leads to its improved physical properties. Considering the position of the Fermi level on the total density of states (DOS), the new compound Nb 2 CuC is structurally less stable than Nb 2 AlC. The total DOS at the Fermi level obtained with GGA is slightly larger than those obtained with LDA. The Nb–C and Nb–A (A = Cu/Al) are covalent bonds, and Nb–Nb bonds lead to antibonding states in both MAX phases. The charge transfer among constituent atoms indicates some ionic character in the chemical bonds of Nb 2 CuC and Nb 2 AlC. Both MAX phases are mechanically and dynamically stable. The Nb 2 CuC is ductile and consequently damage tolerant, whereas Nb 2 AlC is brittle. However, Nb 2 CuC is relatively soft and machinable. In most cases Nb 2 CuC is more elastically anisotropic than Nb 2 AlC, and Nb 2 CuC is expected to be a promising thermal barrier coating material. We propose that Nb 2 CuC is a better coating material for preventing solar heating than Nb 2 AlC, and Nb 2 CuC is expected to be superconductive because its Fermi surface has a nesting nature. Image 1 • Nb 2 CuC is ductile and consequently damage tolerant. • Nb 2 CuC is relatively soft, machinable and elastically more anisotropic than Nb 2 AlC. • Nb 2 CuC is expected to be a promising thermal barrier coating material. • Nb 2 CuC is expected to be a superconductor. [ABSTRACT FROM AUTHOR]

Studies the effect of hydrostatic pressure on pressure, temperature and time dependences of the conductivity in the ab-plane of single crystals with different oxygen concentrations. Parameters of single crystals with different superconducting transition temperature; Peculiarities in the behavior of dependences due to several mechanisms.

Abstract: The system of equations that describes the temporal and spatial evolution of low-energy phonons (l-phonons) is obtained for the cases of plane and axial symmetry. From the solutions of these equations, we discuss the time-resolved measurements of the angular distribution of l-phonons. These show a rather unusual mesa shape with a flat top in the direction normal to the heater. We consider that the flat top is due to the creation of high-energy phonons (h-phonons). [Copyright &y& Elsevier]