| 1. |
- Mattsson, A, et al.
(författare)
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MODEL STUDIES OF THE CHEMISORPTION OF HYDROGEN AND OXYGEN ON CU(100)
- 1987
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 36:14, s. 7389-7401
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Tidskriftsartikel (refereegranskat)abstract
- Atomic chemisorption of hydrogen and oxygen on Cu(100) has been studied using up to 25 copper atoms as a model of the surface. The computational procedure used involves a reduction of the metal atoms to one-electron systems and extensive configuration-interaction calculations of the adsorbate and the cluster-adsorbate bonds. The calculations support the fourfold hollow site as the preferred chemisorption site for oxygen, with a barrier-to-surface migration of 25 kcal/mol. The calculated chemisorption energies for both hydrogen and oxygen, 51 and 90 kcal/mol, respectively, are in good agreement with experimental estimates (56 kcal/mol for hydrogen and 97 kcal/mol for oxygen). The effects of reducing the metal atoms to one-electron systems have been investigated through comparisons with all-electron calculations for Cu5H and Cu5O at the self-consistent-field level and by comparisons to previous calculations on Cu5Cl and Cu9Cl in which the 3d electrons were treated explicitly.
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| 2. |
- Slack, Glen A.
(författare)
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Thermal conductivity of ice
- 1980
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969 .- 0163-1829. ; 22:6, s. 3065-3071
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity of ice, the low-pressure Ih phase of H2O, is reviewed and good agreement is found with the theoretical calculations of its absolute value and temperature dependence. Measurements under pressure show an anomalous decrease in conductivity with decreasing molar volume. This is explained by the negative Grüneisen parameter for the transverse acoustic modes which dominate the heat transport. The conductivity behaves predominantly like that of a wurtzite lattice of rigid mass points with an atomic mass of 18. Some traces of the interaction of the lattice phonons with the higher-lying librational modes can be seen. The volume dependence of the conductivity of the higher-pressure phases of ice and of NH4F is related to that of Ih ice.
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| 3. |
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| 4. |
- Jacobsson, Per, et al.
(författare)
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Thermal conductivity and electrical resistivity of gadolinium as functions of pressure and temperatur
- 1989
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 40:14, s. 9541-9551
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Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity ρ and the thermal diffusivity a of gadolinium have been measured as functions of T in the range 45–400 K. The thermal conductivity λ has been calculated from a and experimental data for the specific-heat capacity, cp. λ can be analyzed in terms of simple models for the lattice and electronic components above the Curie temperature TC≃291.4 K. Below TC an additional term, identified as a magnon (spin-wave) thermal conductivity λm, is found. ρ and λ have also been studied as functions of T and P in the range 150–400 K and 0–2.5 GPa. The Lorenz function L=ρλ/T increases by about 20%/GPa under pressure due to a very strong pressure dependence of the lattice thermal conductivity. The pressure coefficients of ρ and λ are -5.1×10-2 and 0.22 GPa-1, respectively, at 300 K (above TC), and 0 and 0.16 GPa-1 at 200 K (below TC). TC and the spin-reorganization temperature Tr≃219 K both decrease under pressure, at the rates -14.0 and -22.0 K/GPa, respectively. Although the magnitude of λm cannot be accurately calculated from the zero-pressure data for λ, the temperature dependence of dλ/dP allows us to distinguish between several models and assign a value of λm≃1.5 W m-1 K-1, or 16.0% of λ, at 200 K.
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| 5. |
- Petersson, L.-G., et al.
(författare)
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Hydrogen desorption versus electronic structure studies on Ag covered Pd with photoemission and a hydrogen sensitive MOS structure
- 1984
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 30, s. 3055-
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Tidskriftsartikel (refereegranskat)abstract
- With a hydrogen-sensitive Pd metal-oxide-semiconductor structure we have investigated how Ag overlayers affect the hydrogen adsorption and desorption properties of Pd. By varying the concentration of Ag in the top layer, we have continuously changed the distribution of d states close to the Fermi energy as determined by photoemission. For moderate amounts of Ag, only blocking of active hydrogen sites on the Pd surface occurs and no effects due to the variation in the electronic density of states can be detected.
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| 6. |
- Rapp, Östen, et al.
(författare)
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The pressure dependence of of the electron-phonon interaction and the normal state resistivity
- 1981
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 24:1, s. 144-154
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Tidskriftsartikel (refereegranskat)abstract
- Accurate measurements of the electrical resistance as a function of temperature and pressure are reported for Sn, Zr, dhcp La, and V. These measurements cover a temperature region around room temperature and pressures up to 1.3 GPa. From these data, including also our previous measurements for Al and published results for Pb, the pressure dependence of d ρ / dT (the resistivity-temperature derivative) is obtained. This quantity is found to be a significant factor in the pressure dependence of the electron-phonon interaction parameter λ. For the nontransition metals the relative pressure dependence of d ρ / dT is much larger than the compressibility. Therefore the pressure dependence of the superconducting Tc is quantitatively well accounted for by the resistance data for these metals. For the transition metals the pressure dependence of d ρ / dT is relatively smaller and Tc(p) calculated from the resistance data is, at the best, only qualitatively correct. These differences are discussed. Estimates for the pressure dependence of the plasma frequency are obtained.
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| 7. |
- Sundqvist, Bertil
(författare)
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Electrical resistance of nickel in the range 300-725 K and 0-2 GPa
- 1988
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 38:17, s. 12283-12289
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Tidskriftsartikel (refereegranskat)abstract
- The electrical resistance R of Ni has been measured as a function of temperature T and pressure p over the range 300–725 K and 0–2 GPa (0–20 kbar). In contrast to recent reports, we see no anomalies in R(p) at 300 K, and we see no change in sign in dR/dp at the Curie temperature TC. The pressure coefficient of R was -1.82×10-2 GPa-1 at 300 K, increasing with T to a peak value of -2.5×10-2 GPa-1 at TC, above which it rapidly decreased to a value 20% below the room-temperature value. The data are analyzed using simple models; the resistivity at constant volume is found to deviate significantly from the constant-p data above TC and a small anomaly is detected in d(lnR)/dp that could possibly be an effect of band-structure changes at TC.
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| 8. |
- Sundqvist, Bertil, et al.
(författare)
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Pressure dependence of the electron-phonon interaction and Fermi-surface properties of Al, Au, bcc Li, Pb, and Pd
- 1985
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 32:4, s. 2200-2212
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Tidskriftsartikel (refereegranskat)abstract
- The electrical resistance of Li, Pd, Au, and Pb is measured as a function of temperature and pressure in the region -20 °C to +30 °C and 0–1.3 GPa. Self-consistent linear muffin-tin orbital band-structure calculations of these elements and of Al are performed at normal and reduced volumes. Results are obtained for the density of states N(EF), the average Fermi ve- locity, the optical mass, the plasma frequency ω, and the volume dependence of these parameters. The pressure dependence of the electron-phonon interaction λ(p) is obtained from these measurements and the calculated ω(p). For the superconducting elements there is good agreement with the measured superconducting Tc(p). Results from our previous measurements and calculations on Al, V, Nb, and La and published results for ω(p) are included in this comparison. λ(p) increases with pressure for bcc Li and decreases for Pd and Au. Pressure is expected to suppress spin fluctuations much faster than λ(p) in Pd. The possibility of inducing superconductivity by pressure in Pd and bcc Li is discussed. The electronic Grüneisen parameter γe is obtained from λ(p) and the volume dependence of N(EF). Comparison with other results for γe generally shows good agreement.
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| 9. |
- Sundqvist, Bertil, et al.
(författare)
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Pressure-temperature phase boundaries in KC24: Evidence for a kinetically-hindered low-temperature staging transition
- 1986
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 34:5, s. 3532-3535
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Tidskriftsartikel (refereegranskat)abstract
- The pressure-temperature phase diagram of KC24 was mapped out using in-plane resistivity anomalies to identify phase boundaries. Surprisingly, the 300-K staging transitions at 3.4 and 6.4 kbar are found to connect to the 1-bar ordering-stacking transitions at Tu=123 K and Tl=96 K, respectively, whereas the loci of P, T anomalies cannot be equilibrium phase boundaries since the low-P, low-T transitions do not involve stage transformations. We suggest that this unusual behavior is due to kinetic hindering of the low-T staging transitions, predicted by simple equilibrium models and observed in the analogous Li compound. A possible origin of the slow staging kinetics at low T in KC24 is the pinning of discommensurations at Daumas-Herold boundaries.
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| 10. |
- Sundqvist, Bertil, et al.
(författare)
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Pressure-temperature phase diagrams of stage-2-4 potassium-graphite intercalation compounds deduced from anomalies in the basal plane resistivity
- 1987
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 35:15, s. 8231-8242
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Tidskriftsartikel (refereegranskat)abstract
- The basal-plane resistivities ρ of stage-2–4 potassium-graphite intercalation compounds (K-GIC’s) have been measured as functions of temperature T and pressure p using a contactless method. The pressure range investigated was 0–1.4 GPa. For stage-2 K-GIC (KC24) measurements were made in the temperature range 90–300 K, while for the higher-stage materials the range was mainly limited to 245–300 K. In all cases ρ increases with p through the anomalous regime near the phase transitions, whereas dρ/dp is always negative in the stable high-p (high-stage) phases. Approximate p-T phase diagrams are deduced from anomalies in ρ corresponding to the staging and in-plane order-disorder transitions, respectively. In all cases the slopes dp/dT of the phase boundaries for the high-pressure staging transitions are such that the transitions extrapolate to positive T at atmospheric p, although no such transitions have been reported. The low-p staging-ordering phase boundary of KC24 is particularly complex, involving segments with both dp/dT→0 (125<200 K) and dp/dT→∞ (T≊125 K). The p-T diagrams are compared with recent structural experiments and models. We suggest that the complexity of the KC24 phase diagram is attributable to the weakly incommensurate in-plane structure at low p and T.
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