| 1. |
- Andersson, Göran, et al.
(författare)
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A high-pressure cell for electrical resistance measurements at hydrostatic pressures up to 8 GPa : Results for Bi, Ba, Ni, and Si
- 1989
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 65:10, s. 3943-3950
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Tidskriftsartikel (refereegranskat)abstract
- A modified Bridgman anvil high-pressure device, capable of producing hydrostatic pressures up to 8 GPa (80 kbar), was designed and built. The size of the pressure chamber (10 mm in diameter) allows the use of large specimens and simple experimental procedures. Experimental results show that hydrostatic conditions are necessary if accurate quantitative information is desired about the electrical properties of materials under pressure. Accurate data on resistance (and resistivity) versus pressure at 294 K are given for Bi, Ba, Ni, and Si. The initial pressure coefficients of R were d(ln R)dP=0.13, −7.6×10−2, −2.0×10−2, and −0.26 GPa−1, respectively. Barium has a resistance minimum near 0.9 GPa. For Bi we observe sharp transitions at 2.55, 2.7, and 7.7 GPa, and for Ba at 5.55 GPa, but we cannot verify the existence of a transition in Ba near 7 GPa. Neither do we confirm the phase transformation in Ni recently reported to occur above 2.5 GPa. For Si, R(P) agrees very well with a theoretical function calculated from the change in band gap and electron mobility with pressure.
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| 2. |
- Andersson, Göran, et al.
(författare)
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Pressure dependence of the c-axis resistance of stage 2 SbCl5 intercalated graphite to 4 GPa
- 1988
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 65:7, s. 735-738
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Tidskriftsartikel (refereegranskat)abstract
- The c-axis electrical resistance R has been measured under pressure up to 4 GPa (40 kbar) at room temperature for stage 2, HOPG-based SbCl5 intercalated graphite. In addition to the well known ordering transition at 0.3–0.5 GPa a second anomaly in R is observed above 1 GPa, corresponding to a further phase transition which is not completed until above 2.4 GPa. In all phases R depends more strongly on p for the intercalated material than for HOPG, and the total decrease in R is over 80% to 4 GPa.
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| 3. |
- Andersson, Odd E., et al.
(författare)
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C-axis resistance of HgCl2 intercalated graphite as a function of temperature and pressure
- 1989
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Ingår i: Synthetic Metals volume 34. - Lausanne : Elsevier Sequoia SA. ; , s. 485-490
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Konferensbidrag (refereegranskat)abstract
- The c-axis resistance of stage 3 HgCl2 intercalated graphite has been measured as a function of temperature T and pressure p in the range 40 to 300 K and up to 1 GPa (10 kbar). The absolute resistivity and its T- and p- dependence are all in good agreement with data for other acceptor compounds. The measurements show that a previosly unknown phase transformation occurs above 0.4 GPa. Below 250 K the high pressure phase is metastable down to zero pressure, and an x-ray diffraction analysis of metastable material shows that no stage change occurs. The transition thus probably leads to a different in-plane structure characterized by a more densely packed intercalate layer.
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| 4. |
- Andersson, Odd E., et al.
(författare)
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Structure, c-axis resistivity, and p-T phase diagram of SbCl5 intercalated graphite
- 1989
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Ingår i: Synthetic Metals volume 34. - Lausanne : Elsevier Sequoia SA. ; , s. 187-192
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Konferensbidrag (refereegranskat)abstract
- Experimental data are reported for the c-axis resistivity varrhoc of stages n = 3,4,5 and 8 SbCl5 intercalated graphite as a function of T and p, in the range 40 – 300 K and 0-0.5 GPa (5 kbar). varrhoc varied in a systematic way with p, T, and n. Well ordered low-T phases were obtained for all stages; disordering at 200 – 235 K gave rise to well defined multiple anomalies in varrhoc. We also report x-ray diffraction data on the stage 2 compound: evidence was found for large variations in the in-plane structure even for nominally identical samples.
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| 5. |
- Jacobsson, Per, et al.
(författare)
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Pressure dependence of the thermal and electrical conductivities of the intermetallic compounds AuCu and AuCu3
- 1988
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Ingår i: Journal of Physics and Chemistry of Solids. - : Elsevier BV. - 0022-3697 .- 1879-2553. ; 49:4, s. 441-450
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Tidskriftsartikel (refereegranskat)abstract
- The thermal diffusivity, a, electrical resistivity, ρ, and Seebeck coefficient, S, of ordered and disordered AuCu3 and AuCu have been measured as functions of T and P in the range 100–300 K and 0–2 GPa, and the thermal conductivity, λ, has been calculated from the data for a. The experimental data for ρ agree well with literature data. The ρ dependence of ρ and λ differs significantly between ordered and disordered specimens, but apart from the effect of impurity scattering the disordered materials behave much like the noble metals. For the temperature-dependent part of p (and λ) the P dependence differs by a factor of 2–3 between ordered and disordered states. This is shown to result from the difference in electron band structure, as reflected also in the thermoelectric parameter ξ. The P dependence of the relatively large lattice thermal conductivity of these materials causes the Lorenz ratio L = λρ/T to increase with ρ in all cases.
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| 6. |
- 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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| 7. |
- Jacobsson, Per, et al.
(författare)
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Thermal conductivity and Lorenz function of zinc under pressure
- 1988
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Ingår i: International journal of thermophysics. - 0195-928X .- 1572-9567. ; 9:4, s. 577-585
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity lambda and the Lorenz function L of polycrystalline zinc have been calculated from measured values of the thermal diffusivity a and the electrical resistivity gamma as functions of pressure P up to 2 GPa at room temperature. The effects of convection in, and freezing of, the pressure transmitting medium are discussed. Both lambda and L increase with increasing P, with pressure coefficients of 8.7×10–2 and 1.5×10–2 GPa–1, respectively. The volume dependence of L is found to be similar to that found for other simple metals. Data are also given for the Seebeck coefficient S as a function of P and for a(T) and lambda(T) between 55 and 300 K.
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| 8. |
- Jacobsson, Per, et al.
(författare)
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Thermal diffusivity of zinc as a function of pressure and temperature
- 1985
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Ingår i: High Temperatures - High Pressures Vol. 17. - London : Pion Press. - 0 85086 124 1 ; , s. 103-109
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Konferensbidrag (refereegranskat)abstract
- The thermal diffusivity and the electric resistivity of polycrystalline zinc have been measured as functions of temperature between 90 and 480 K at atmospheric pressure, and as functions of pressure up to 2 GPa (20 kbar) at room temperature. The pressure and temperature dependence of the thermal conductivity has been calculated by using literature data for the specific heat capacity. No minimum was found in the thermal conductivity at low temperatures. The pressure coefficient of the thermal conductivity was found to be 4.1 x 10-2 /GPa, which indicates that the Lorenz function of zinc decreases with increasing pressure.
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| 9. |
- Jarlborg, Thomas, et al.
(författare)
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Electron-Phonon Interaction of fcc and dhcp La under Pressure
- 1987
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Ingår i: Japanese Journal of Applied Physics, volume 26, Supplement 26-3-2. - : The Japan Society of Applied Physics. ; , s. 919-920
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Konferensbidrag (refereegranskat)abstract
- The pressure dependence of the electron-phonon interaction of La has been studied for both phases by two methods: One is a calculation of λ and the other uses the calculated plasma frequency and the measured temperature and pressure dependence of the electrical resistivity. These results as well as a calculation of the spin-fluctuation contribution suggest that quenching of spin-fluctuations with pressure contribute to the increase of Tc with pressure in La.
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| 10. |
- Jarlborg, Thomas, et al.
(författare)
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Resistivity, bandstructure and superconductivity of DHCP and FCC La under pressure
- 1989
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 1:44, s. 8407-8424
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Tidskriftsartikel (refereegranskat)abstract
- Electronic and superconducting properties of DHCP and FCC La are studied both by measurements of the electrical resistance as a function of temperature and pressure and by calculations of the band structure, Fermi surface properties and the electron-phonon interaction lambda . The importance of a hydrostatic environment for reliable resistance measurements is stressed. The transport properties of both phases are similar with small and negative values of the pressure coefficient of resistance. In contrast, the band structure calculations show large differences between the two phases, particularly in the pressure dependence, e.g. of the density of states (DOS) and the plasma frequency. Two new remarkable properties of La have been found, adding to previously known anomalies. One is a strong temperature dependence of the pressure coefficient of resistance which decreases with increasing temperature in both phases. The other is a strong pressure dependence of the plasma frequency in the FCC phase, which is larger than in any other element known to us. From these results the pressure dependence of lambda is obtained by two independent methods for each phase. For FCC, both methods give d ln lambda /dp=0.05+or-0.02 GPa-1, while for DHCP, a decrease of lambda with pressure or an almost pressure independent lambda is suggested. These results cannot fully explain the observed Tc(p) in the FCC phase and fail completely in the DHCP phase. The contribution from spin fluctuations is calculated approximately and found to account qualitatively for this discrepancy. In particular, the DOS decreases slowly with pressure in the FCC phase which gives some decrease of the spin fluctuation contribution in this phase, while in the DHCP phase the DOS decreases strongly, leading to suppression of the spin fluctuations under pressure.
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