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Olivine-like NaFePO4 glasses and nanocomposites are promising materials for cathodes in sodium batteries. Our previous studies focused on the preparation of NaFePO4 glass, transforming it into a nanocomposite using high-pressure–high-temperature treatment, and comparing both materials' structural, thermal, and DC electric conductivity. This work focuses on specific features of AC electric conductivity, containing messages on the dynamics of translational processes. Conductivity spectra measured at various temperatures are scaled by apparent DC conductivity and plotted against frequency scaled by DC conductivity and temperature in a so-called master curve representation. Both glass and nanocomposite conductivity spectra are used to test the (effective) exponent using Jonscher's scaling law. In both materials, the values of exponent range from 0.3 to 0.9, with different relation to temperature. It corresponds to the electronic conduction mechanism change from low-temperature Mott's variable range hopping (between Fe2+/Fe3+ centers) to phonon-assisted hopping, which was suggested by previous DC measurements. Following the pressure treatment, AC conductivity activation energies were reduced from E A C ≈ 0.40   e V for glass to E A C ≈ 0.18   e V for nanocomposite and are lower than their DC counterpart, following a typical empirical relation with the value of the exponent. While pressure treatment leads to a 2–3-orders-of-magnitude rise in the AC and apparent DC conductivity due to the reduced distance between the hopping centers, a nonmonotonic relation of AC power exponent and temperature is observed. It occurs due to the disturbance of polaron interactions with Na+ mobile ions. [ABSTRACT FROM AUTHOR]

Olivine-like NaFePO4 glasses and nanocomposites are promising materials for cathodes in sodium batteries. Our previous studies focused on the preparation of NaFePO4 glass, transforming it into a nanocomposite using high-pressure–high-temperature treatment, and comparing both materials’ structural, thermal, and DC electric conductivity. This work focuses on specific features of AC electric conductivity, containing messages on the dynamics of translational processes. Conductivity spectra measured at various temperatures are scaled by apparent DC conductivity and plotted against frequency scaled by DC conductivity and temperature in a so-called master curve representation. Both glass and nanocomposite conductivity spectra are used to test the (effective) exponent using Jonscher’s scaling law. In both materials, the values of exponent range from 0.3 to 0.9, with different relation to temperature. It corresponds to the electronic conduction mechanism change from low-temperature Mott’s variable range hopping (between Fe2+/Fe3+ centers) to phonon-assisted hopping, which was suggested by previous DC measurements. Following the pressure treatment, AC conductivity activation energies were reduced from EAC≈0.40 eV for glass to EAC≈0.18 eV for nanocomposite and are lower than their DC counterpart, following a typical empirical relation with the value of the exponent. While pressure treatment leads to a 2–3-orders-of-magnitude rise in the AC and apparent DC conductivity due to the reduced distance between the hopping centers, a nonmonotonic relation of AC power exponent and temperature is observed. It occurs due to the disturbance of polaron interactions with Na+ mobile ions.

We report an ab initio study of Sb2S3, Sb2Se3, and Bi2S3 sesquichalcogenides at hydrostatic pressures of up to 60 GPa. We explore the possibility that the C2/m, C2/c, the disordered Im-3m, and the I4/mmm phases observed in sesquichalcogenides with heavier cations, viz. Bi2Se3, Bi2Te3, and Sb2Te3, could also be formed in Sb2S3, Sb2Se3, and Bi2S3, as suggested from recent experiments. Our calculations show that the C2/c phase is not energetically favorable in any of the three compounds, up to 60 GPa. The C2/m system is also unfavorable for Sb2S3 and Bi2S3; however, it is energetically favorable with respect to the Pnma phase of Sb2Se3 above 10 GPa. Finally, the I4/mmm and the disordered body-centered cubic-type Im-3m structures are competitive in energy and are energetically more stable than the C2/m phase at pressures beyond 30 GPa. The dynamical stabilities of the Pnma, Im-3m, C2/m, and I4/mmm structural phases at high pressures are discussed for the three compounds. [ABSTRACT FROM AUTHOR]

We report an ab initio study of Sb2S3, Sb2Se3, and Bi2S3 sesquichalcogenides at hydrostatic pressures of up to 60 GPa. We explore the possibility that the C2/m, C2/c, the disordered Im-3m, and the I4/mmm phases observed in sesquichalcogenides with heavier cations, viz. Bi2Se3, Bi2Te3, and Sb2Te3, could also be formed in Sb2S3, Sb2Se3, and Bi2S3, as suggested from recent experiments. Our calculations show that the C2/c phase is not energetically favorable in any of the three compounds, up to 60 GPa. The C2/m system is also unfavorable for Sb2S3 and Bi2S3; however, it is energetically favorable with respect to the Pnma phase of Sb2Se3 above 10 GPa. Finally, the I4/mmm and the disordered body-centered cubic-type Im-3m structures are competitive in energy and are energetically more stable than the C2/m phase at pressures beyond 30 GPa. The dynamical stabilities of the Pnma, Im-3m, C2/m, and I4/mmm structural phases at high pressures are discussed for the three compounds.

At present, metal hydrides are considered highly promising materials for phonon-mediated superconductors that exhibit high values of the critical temperature. In the present study, the superconducting properties of the compressed selenium hydride in its simplest form (HSe) are analyzed, toward quantitative characterization of this phase. By using the state-of-art Migdal-Eliashberg formalism, it is shown that the critical temperature in this material is relatively high ( T c = 4 2. 6 5 K) and surpasses the level of magnesium diboride superconductor, assuming that the Coulomb pseudopotential takes value of 0. 1. Moreover, the employed theoretical model allows us to characterize other pivotal thermodynamic properties such as the superconducting band gap, the free energy, the specific heat, and the critical magnetic field. In what follows, it is shown that the characteristic thermodynamic ratios for the aforementioned parameters differ from the predictions of the Bardeen-Cooper-Schrieffer theory. As a result, we argue that strong-coupling and retardation effects play important role in the discussed superconducting state, which cannot be described within the weak-coupling regime. [ABSTRACT FROM AUTHOR]

Bilayer molybdate Sr 3 Mo 2 O 7 has been successfully synthesized by a modified solid-state reaction method. Magnetization measurements show that the compound is a paramagnetic material with a weak spin-glass state below about 4.5 K. Fitting to the magnetic susceptibility under a high magnetic field based on the Currie–Weiss law yields a magnetic moment of about 1.61 μ B per Mo atom. The temperature dependence of resistivity exhibits a metallic behaviour in wide temperature region from 20 K to 300 K, but a slight upturn of resistivity with the behaviour of ρ ∝ − ln ⁡ (T) is observed at temperatures below about 20 K. Negative magneto-resistance behaviour has also been observed in the temperature region with resistivity upturning. Both effects indicate that a Kondo-like scattering occurs in the material. Resistivity measurements under high pressures up to 33.7 GPa are carried out, no superconductivity above 2 K has been observed, which is in contradiction to the theoretical prediction. We argue that the absence of superconductivity maybe because the flat-band is still too far away from the Fermi energy. [ABSTRACT FROM AUTHOR]

For La1–xPrxCoO3 cobaltites (x = 0, 0.1, 0.2, and 0.3), the dependence of magnetic susceptibility χ(T) is studied in the temperature range 5–400 K. Also, the crystal structure of these cobaltites is investigated, and the effect of pressure up to 2 kbar on their susceptibility is measured at T=78, 150, and 300 K. The specific dependencies χ(T) and the large negative pressure effect are assumed to arise from Co3+ ions contribution to the total susceptibility evaluated using La1−xPrxAlO3 as a reference system. The obtained experimental data on temperature and pressure effects in magnetism are analyzed within a two‐level model with energy gap Δ between the ground state of the system with zero spin of Co3+ ions and the excited higher‐spin state. In this model, magnetism of Co3+ ions is determined by the temperature‐induced population of the excited state, and magnitude of the pressure effect is governed by the volume dependence of Δ. The results of the analysis, supplemented by the theoretical calculations of the electronic structures of LaCoO3 and PrCoO3, indicate significant increase in Δ with decrease in the unit cell volume both under hydrostatic pressure and by substituting La with Pr having a smaller ionic radius. [ABSTRACT FROM AUTHOR]

For La1–xPrxCoO3 cobaltites (x = 0, 0.1, 0.2, and 0.3), the dependence of magnetic susceptibility χ(T) is studied in the temperature range 5–400 K. Also, the crystal structure of these cobaltites is investigated, and the effect of pressure up to 2 kbar on their susceptibility is measured at T=78, 150, and 300 K. The specific dependencies χ(T) and the large negative pressure effect are assumed to arise from Co3+ ions contribution to the total susceptibility evaluated using La1−xPrxAlO3 as a reference system. The obtained experimental data on temperature and pressure effects in magnetism are analyzed within a two‐level model with energy gap Δ between the ground state of the system with zero spin of Co3+ ions and the excited higher‐spin state. In this model, magnetism of Co3+ ions is determined by the temperature‐induced population of the excited state, and magnitude of the pressure effect is governed by the volume dependence of Δ. The results of the analysis, supplemented by the theoretical calculations of the electronic structures of LaCoO3 and PrCoO3, indicate significant increase in Δ with decrease in the unit cell volume both under hydrostatic pressure and by substituting La with Pr having a smaller ionic radius. [ABSTRACT FROM AUTHOR]

The crystal structure, magnetic susceptibility as a function of temperature χ(T) in the range 5–400 K, and the hydrostatic pressure effect on χ at fixed temperatures T = 78, 150, and 300 K, were studied in perovskite-like compounds La1−xPrxCoO3 (x = 0, 0.1, 0.2, and 0.3). The obtained experimental data were analyzed using a two-level model with an energy gap Δ between the ground and excited states of the system that correspond to the spin values S = 0 and 1 for Co3+ ions. In this model, the magnetism of Co3+ ions, which determines the features of the χ (T) dependence, is ensured by the temperature-induced change in the population of the excited state. The anomalously large magnitude of the observed pressure effect is associated with the high sensitivity of Δ to changes in the lattice volume, under the influence of both hydrostatic and chemical pressures, when La is replaced by the smaller Pr ion in the considered system. Theoretical calculations of the electronic structure for the boundary compounds LaCoO3 and PrCoO3 confirm the significant increase in the excitation energy Δ with a decrease in the lattice volume, and also support the scenario of a spin crossover between the states of cobalt ions with low and intermediate spin values. [ABSTRACT FROM AUTHOR]

At present, hydrogen-based compounds constitute one of the most promising classes of materials for applications as phonon-mediated high-temperature superconductors. Herein, the behavior of the superconducting phase in tellurium hydride (HTe) at high pressure (p = 300 GPa) is analyzed in detail, by using the isotropic Migdal–Eliashberg equations. The chosen pressure conditions are considered here as a case study which corresponds to the highest critical temperature value (T c) in the analyzed material, as determined within recent density functional theory simulations. It is found that the Migdal–Eliashberg formalism, which constitutes a strong-coupling generalization of the Bardeen–Cooper–Schrieffer (BCS) theory, predicts that the critical temperature value ( T c = 5 2. 7 3 K) is higher than previous estimates of the McMillan formula. Further investigations show that the characteristic dimensionless ratios for the thermodynamic critical field, the specific heat for the superconducting state, and the superconducting band gap exceed the limits of the BCS theory. In this context, also the effective electron mass is not equal to the bare electron mass as provided by the BCS theory. On the basis of these findings it is predicted that the strong-coupling and retardation effects play pivotal role in the superconducting phase of HTe at 300 GPa, in agreement with similar theoretical estimates for the sibling hydrogen and hydrogen-based compounds. Hence, it is suggested that the superconducting state in HTe cannot be properly described within the mean-field picture of the BCS theory. [ABSTRACT FROM AUTHOR]

In this article, we review how pressure effects in pores affect both the physics of the confined fluid and the properties of the host porous material. Molecular simulations in which high-pressure effects were observed are first discussed; we will see how the strong dependence on bulk phase pressure of the freezing temperature of a fluid confined in nanopores can be explained by important variations of the pressure within the pore. We then discuss recent works in which direct calculations of the pressure tensor of fluids confined in pores provide evidence for large pressure enhancements. Finally, practical applications of these pressure effects in which gas adsorption in microporous solids (pore size < 2 nm) was found to enhance their mechanical properties by increasing the elastic modulus by a factor 4 are discussed. [ABSTRACT FROM PUBLISHER]

The properties of the superconducting state in the Cmca phase of silane (SiH4) at the pressure of 250 GPa have been considered. In particular, the critical temperature (Tc), the free energy difference between the superconducting and normal state (ΔF = FS - FN ), the thermodynamic critical field (HE) and the specific heat jump (ΔC = CS - CN) have been determined. It has been shown that the dimensionless ratios: RH = TCCN(TC)/HBC(0) and RC = ΔC(TC)/CN(TC) assume the values: RH(μ) € (0.147,0.154) and Rc(μ*) 6 (2.20,1.79), where the symbol μ* denotes the Coulomb pseudopotential and &mu* (0.1,0.3). [ABSTRACT FROM AUTHOR]

In this paper, the thermodynamic properties of the superconducting state in the metallic hydrogen under the pressure at 347 GPa have been determined. In the framework of the Eliashberg formalism, it has been shown that the characteristic thermodynamic parameters deviate from the predictions of the BCS theory. In particular, the ratio ΔC(TC)/CN(TC) decreases from 1.96 to 1.72 depending on the assumed value of the Coulomb pseudopotential (μ* ∈ 〈0.08, 0.15〉). On the other hand, the ratio increases from 0.150 to 0.158. [ABSTRACT FROM AUTHOR]

The thermodynamic parameters of the superconducting state in PtH at the pressure 76GPa have been examined. The calculations have been carried out in the framework of the Eliashberg formalism. It has been found that the critical temperature ( [ABSTRACT FROM AUTHOR]

Abstract: The ab initio calculations suggest that the superconducting state in CaH6 under the pressure (p) at 150 GPa has the highest critical temperature among the examined hydrogen-rich compounds. For this reason, the relevant thermodynamic parameters of the superconducting state in CaH6 have been determined; a wide range of the Coulomb pseudopotential has been assumed: μ ⋆∈〈0.1,0.3〉. It has been found that: (i) The critical temperature (T C ) changes in the range from 243 K to 180 K (ii) The values of the ratio of the energy gap to the critical temperature (R Δ ≡ 2Δ(0)/k B T C ) can be found in the range from 5.42 to 5.02. (iii) The ratio of the specific heat jump (ΔC(T C )) to the value of the specific heat in the normal state (C N (T C )), which has been represented by the symbol R C , takes the values from 3.30 to 3.18. (iv) The ratio , where H C (0) denotes the critical thermodynamic field, changes from 0.122 to 0.125. The above results mean that even for the strong electron depairing correlations the superconducting state in CaH6 is characterized by a very high value of T C , and the remaining thermodynamic parameters significantly deviate from the predictions of the BCS theory. The study has brought out the expressions that correctly predict the values of the thermodynamic parameters for the superconducting state in CaH6 and for the compounds: SiH4(H2)2, Si2H6, B2H6, SiH4, GeH4, and PtH. Next, in the whole family of the hydrogen-rich compounds, the possible ranges of the values have been determined for T C , R Δ, R C , and R H . It has been found that the maximum value of the critical temperature can be equal to 764 K, which very well correlates with T C for metallic hydrogen (p = 2 TPa). Other parameters (R Δ, R C , and R H ) should not deviate from the predictions of the BCS theory more than the analogous parameters for CaH6. [Copyright &y& Elsevier]

The thermodynamic properties of the superconducting state in CaLi at 60 GPa have been described in the paper. The numerical analysis has been carried out in the framework of the Eliashberg formalism. It has been shown that: (i) the critical value of the Coulomb pseudopotential is equal to 0.20, which corresponds to the value of 1795 meV for the Coulomb potential; (ii) the critical temperature ( T) cannot be correctly calculated by using the Allen-Dynes (AD) formula; (iii) the dimensionless ratios: $T_{C}C^{N} (T_{C} )/H^{2}_{C} (0 )$, ( C( T)− C( T))/ C( T) and 2Δ(0)/ k T take the non-BCS values: 0.157, 1.78 and 3.85, respectively. The symbol C represents the specific heat in the normal state, C denotes the specific heat in the superconducting state, H(0) is the thermodynamic critical field near the temperature of zero Kelvin, and Δ(0) is the order parameter; (iv) the ratio of the electron effective mass ( $m^{\star}_{e}$) to the electron band mass ( m) assumes a high value, in the whole range of the temperature, where the superconducting state exists. The maximum of $m^{\star}_{e}/m_{e}$ is equal to 2.15 for T= T. [ABSTRACT FROM AUTHOR]

A first principles calculation of the lattice dynamical properties of rutile SnO2 has been performed using density functional perturbation theory at ambient and high-pressure conditions to understand the pressure-induced phase transition. The calculated zone centre phonon modes at ambient and high pressures have been compared with Raman scattering and infrared measurements. Full phonon dispersion curves and phonon densities of states and Raman intensities at high pressures are calculated and given for the first time in literature. The ferroelastic transition from the rutile to the CaCl2-type structure was confirmed. It is clearly illustrated that the first transition is associated with macroscopic shear instability which arises from the strong coupling between elastic constants and softening of Raman active B1g mode. The observed pressure of phase transition in experimental measurements was reproduced more accurately than in previous calculations, and the difference between observed and calculated transition pressure is only of the order of 2%. The mode Grüneisen parameter is quantitatively as well as qualitatively different from the earlier reported values. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The thermodynamic parameters of the superconducting state, that gets induced in the metallic molecular hydrogen under the influence of the pressure at 414 GPa (T C  = 84 K), have been determined. The calculations have been conducted in the framework of the three-band Eliashberg equations. The order parameters (Δ α ) and the wave function renormalization factors (Z α ) have been derived; the symbol α denotes the band index: α ∈ {a, b, c}. It has been stated that the dimensionless ratios 2Δ α (0)/k B T C are equal to: 5.55, 3.96 and 3.53, respectively. Next, the total normalized function of the density of states, the free energy, the thermodynamic critical field and the specific heat have been determined. The obtained results differ significantly from the results achieved in the framework of the one-band Eliashberg model for the comparable value of the pressure (p = 428 GPa). In the last step, the values of the wave function renormalization factors have been estimated for T C . It allowed us to calculate the maximum value of the electron effective mass in a given band . The following results have been achieved: , and , where stands for the electron band mass. [Copyright &y& Elsevier]

The thermodynamic properties of the superconducting state that induces in selenium at the pressure of 100 GPa have been described in the paper. In the framework of the Eliashberg theory values of the energy gap at the temperature of close to zero Kelvin and electron effective mass have been determined. Our study shows that the ratio of the electron effective mass to electron band mass (m"e/me) in the entire range of the superconducting state existence takes a high value and its maximum equals 1:505 for T = TC. Furthermore, it has been shown that the dimensionless ratio: 2Δ (0) /kBTC deviates from the predictions of the conventional BCS theory. [ABSTRACT FROM AUTHOR]

Abstract: The thermodynamic parameters of the superconducting state for SiH4(H2)2 compound under the pressure at 250 GPa have been investigated. The calculations have been made in the framework of the Eliashberg formalism. In particular, the free energy difference () between the superconducting (S) and normal (N) state, the specific heat (C), as well as, the thermodynamic critical field () have been determined. It has been shown that the considered thermodynamic functions are beyond the BCS predictions; the ratio decreases from to with increase of the Coulomb pseudopotential (), and the parameter increases from to . The numerical results have been supplemented with the interpolation approach. [Copyright &y& Elsevier]

The thermodynamic parameters of the superconducting state in calcium under the pressure of 161 GPa have been calculated within the framework of the Eliashberg approach. It has been shown that the value of the Coulomb pseudopotential is high ( $\mu _{{\rm C}}^{*} = 0.24$) and the critical temperature ( TC = 25 K) should be determined from the modified Allen-Dynes formula. In addition, it has been found that the basic dimensionless ratios of the thermodynamic parameters significantly diverge from the BCS predictions, and take the following values: (i) The zero-temperature energy gap to the critical temperature ( $R_{1} \equiv 2\Delta (0)/k_{{\rm B}} T_{{\rm C}} $) is equal to 4.01. (ii) The ratio $R_{2} \equiv {\left( {C^{{\rm S}} (T_{{\rm C}} )- C^{{\rm N}} (T_{{\rm C}} )} \right)}/C^{{\rm N}} (T_{{\rm C}} )$ equals 2.17, where CS and CN denote the specific heats for the superconducting and normal states, respectively. (iii) The quantity $R_{3} \equiv T_{{\rm C}} C^{{\rm N}} (T_{{\rm C}} )/H_{{\rm C}}^{2} (0) = 0.158$, where HC indicates the thermodynamic critical field. Finally, it has been proven that the electron effective mass is large and takes the maximum of 2.32 me at TC. [ABSTRACT FROM AUTHOR]

We report a successful observation of pressure-induced superconductivity in a topological compound Bi21e3 with Tc of ∼3 K between 3 to 6 GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the holetype carrier in the pressure-induced superconducting Bi2Te3 single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi2Te3 due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor [ABSTRACT FROM AUTHOR]

We report a successful observation of pressure-induced superconductivity in a topological compound Bi21e3 with Tc of ∼3 K between 3 to 6 GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the holetype carrier in the pressure-induced superconducting Bi2Te3 single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi2Te3 due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor [ABSTRACT FROM AUTHOR]

Abstract: The dependence of two-level systems in disordered atomic chain on pressure, both positive and negative was studied numerically. The disorder was produced through the use of interatomic pair potentials having more than one energy minimum. It was found that there exists a correlation between the energy separation of the minima of two-level systems Δ and the variation of this separation with pressure. The correlation may have either positive or negative sign, implying that the asymmetry of two-level systems may in average increase or decrease with pressure depending on the interplay of different interactions between atoms in disordered state. The values of Δ depend on the sign of pressure. [Copyright &y& Elsevier]

We report here on a pressure-induced phase transition in nanocrystalline La-deficient perovskite oxide, synthesised through the sol-gel technique, using Mossbauer spectroscopy, electrical resistivity and X-ray diffraction measurements at room temperature. At ambient pressure, the high-spin Fe3+ ion is distributed in two different environments. Below 0.6 GPa, a sudden dip in the resistivity curve and a single-environment Fe3+ doublet in the Mossbauer pattern are indicative of lattice compaction. A high-spin to low-spin Fe3+ transition at 2.1 GPa, and an orthorhombic to monoclinic structural transformation at 4.9 GPa, as revealed through Mossbauer patterns, are also associated with sudden dips in the electrical resistivity. X-ray diffraction patterns support the results. [ABSTRACT FROM AUTHOR]

Abstract: Open-loop dynamic responses of vaporizing droplet to high-frequency pressure waves are theoretically-numerically investigated. Conservation equations for liquid and gas phases are solved separately for spherically symmetric vaporization and transports, and flow parameters are matched at liquid–vapor interfacial boundary. The pressure-coupled response of the droplet vaporization is commanded by the coupling between the acoustic and thermal processes occurring in an immediate vicinity of the interfacial boundary. The vaporization response strongly depends on the ambient pressure, and the acoustic instabilities are expected at higher pressures and lower frequencies. [Copyright &y& Elsevier]

The density dependence of the structural relaxation time of water has been determined by inelastic ultraviolet scattering (IUVS). The observed trend is opposite to the expected one. This striking experimental result calls for further investigations. [ABSTRACT FROM AUTHOR]

High-pressure X-ray diffraction studies on gadolinium sesquioxide (Gd2O3) have been carried out up to a pressure of ∼25 GPa in a diamond-anvil cell at room temperature. Gadolinium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase at around 12 GPa. The high-pressure phase has been identified as a hexagonal La2O3-type structure. The bulk modulus and its pressure derivative of this phase have been calculated. [ABSTRACT FROM AUTHOR]

The pressure dependence of the components of the recombination current at threshold in 1.3-μm GaInNAs single quantum-well lasers is presented using for the first time high-pressure spontaneous emission measurements up to 13 kbar. It is shown that, above 6 kbar, the rapid increase of the threshold current with increasing pressure is associated with the unusual increase of the Auger-related nonradiative recombination current, while the defect-related monomolecular nonradiative recombination current is almost constant. Theoretical calculations show that the increase of the Auger current can be attributed to a large increase in the threshold carrier density with pressure, which is mainly due to the increase in the electron effective mass arising from the enhanced level-anticrossing between the GaInNAs conduction band and the nitrogen level. [ABSTRACT FROM PUBLISHER]

We report on the epitaxial growth of YSr/sub 2/Cu/sub 2.75/Mo/sub 0.25/O/sub 7-/spl delta// (YSCMO) thin films by pulsed laser ablation, and discuss the superconducting find normal state transport properties of microbridges patterned from such films. To investigate the dopant oxygen mobility of this material, we have used electrical biases applied at near room temperature to induce long range displacement of chain oxygen vacancies in these microbridges. We find that with electromigration, the T/sub c/ of the microbridges can be raised to |60 K. This transition temperature is higher than any previously achieved for this compound, including the T/sub c/'s achieved. As result of extended very high pressure oxygen anneals, or by high pressure in situ measurements. Micro-Raman spectroscopy measurements have been used to examine and characterize the oxygen order in the film before and After electromigration. These measurements indicate that, as suggested by the final T/sub c/ achieved, a very high degree of oxygenation and chain oxygen order can be induced in the microbridge by this process. Thus the as-grown properties of YSCMO appear to be dominated by the low level of oxygenation and the low degree of oxygen homogeneity obtained by normal annealing processes. [ABSTRACT FROM PUBLISHER]