| 11. |
- Jacobsson, Per, et al.
(author)
-
Thermal conductivity and electrical resistivity of gadolinium as functions of pressure and temperatur
- 1989
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 40:14, s. 9541-9551
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Journal article (peer-reviewed)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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| 12. |
- Jacobsson, Per, et al.
(author)
-
Thermal conductivity and Lorenz function of zinc under pressure
- 1988
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In: International journal of thermophysics. - 0195-928X .- 1572-9567. ; 9:4, s. 577-585
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Journal article (peer-reviewed)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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| 13. |
- Jacobsson, Per, et al.
(author)
-
Thermal diffusivity of zinc as a function of pressure and temperature
- 1985
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In: High Temperatures - High Pressures Vol. 17. - London : Pion Press. - 0 85086 124 1 ; , s. 103-109
-
Conference paper (peer-reviewed)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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| 14. |
- Jarlborg, Thomas, et al.
(author)
-
Electron-Phonon Interaction of fcc and dhcp La under Pressure
- 1987
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In: Japanese Journal of Applied Physics, volume 26, Supplement 26-3-2. - : The Japan Society of Applied Physics. ; , s. 919-920
-
Conference paper (peer-reviewed)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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| 15. |
- Jarlborg, Thomas, et al.
(author)
-
Resistivity, bandstructure and superconductivity of DHCP and FCC La under pressure
- 1989
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 1:44, s. 8407-8424
-
Journal article (peer-reviewed)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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| 16. |
- Lundberg, Bo, et al.
(author)
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Basal plane resistivity and phase diagram of HNO3 intercalated graphite in the range 130–320 K and 0–1.6 GPa
- 1986
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In: Solid State Communications. - : Elsevier Science Ltd.. - 0038-1098 .- 1879-2766. ; 58:10, s. 747-751
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Journal article (peer-reviewed)abstract
- The basal plane resistivity varrho of stages 3–5 HNO3 intercalated graphite has been measured as a function of temperature T and pressure p in the range 130–320 K and 0–1.6 GPa (16 kbar). A contactless method was used. The phase boundary of the 250 K ordering transition at zero pressure was traced up to 320 K through the corresponding anomaly in varrho. The pressure dependence of varrho was strongly stage dependent, such that for stages 3, 4 and 5 the observed pressure coefficients (1/varrho)dvarrho/dp were approximately 0.08, −0.08, and −0.22 GPa−1, respectively, near zero pressure.
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| 17. |
- Lundberg, Bo, et al.
(author)
-
Pressure-dependent electrical conductivity of polypyrrole
- 1985
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In: Molecular Crystals and Liquid Crystals vol. 118. - : Informa UK Limited. - 0026-8941. ; , s. 155-158
-
Conference paper (peer-reviewed)abstract
- The results of pressure dependent electrical conductivity measurements in polypyrrole are consistent with a simple extension of the variable-range-hopping model of electronic transport in disordered media.
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| 18. |
- Lundberg, Bo, et al.
(author)
-
Pressure effects on electrical conductivities in intercalated graphite and doped polypyrrole
- 1984
-
In: Journal de Physique Colloque vol. 45. - : EDP Sciences. - 0449-1947. ; , s. 213-216
-
Conference paper (peer-reviewed)abstract
- We have measured the pressure dependence up to 2.5 GPa of the electrical resistance of the acceptor intercalated graphites CnFeCl3, CnSbF5, and CnHNO3. The slope of resistance versus pressure is approximately the same in all cases. Two different types of high pressure transitions are observed in CnSbF5 and CnHNO3. The results of electrical resistance measurements under pressure in polypyrrole are consistent with a simple extension of the variable-range-hopping model. We infer for this material that the density of states at the Fermi level increases with pressure.
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| 19. |
- Lundberg, Bo, et al.
(author)
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Resistivity of a composite conducting polymer as a function of temperature, pressure, and environment: Applications as a pressure and gas concentration transducer
- 1986
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 60:3, s. 1074-1079
-
Journal article (peer-reviewed)abstract
- The resistivity of a commercial carbon-filled composite conducting polymer (ET-Semicon[large-closed-square]) has been measured as a function of temperature between 80 and 400 K and under pressure up to 1.5 GPa (15 kbar). Large changes in resistivity were observed. The resistivity was also very sensitive to the presence of certain solvents and hydrocarbons. The results are explained as percolation effects caused by changes in volume due to pressure, thermal expansion, or dissolved solvents. The material studied is found to have a wide range of potential applications for pressure measurements and as a transducer for gas or liquid concentration.
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| 20. |
- Neve, Jesper, et al.
(author)
-
Electron band structure, resistivity, and the electron-phonon interaction for niobium under pressure
- 1983
-
In: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 28:2, s. 629-637
-
Journal article (peer-reviewed)abstract
- Accurate measurements of the electrical resistance of Nb are presented as a function of temperature and pressure in the region 0-40°C and 0-1 GPa. From these measurements and published results for the compressibility and the pressure dependence of the superconducting transition temperature Tc we evaluate the pressure dependence of the electron-gas plasma frequency ω(p). The electronic structure of Nb is calculated from a self-consistent linear muffin-tin orbital method and results are obtained for the pressure dependence of the density of states at the Fermi surface, the root mean square over the Fermi surface of the Fermi velocity, the optical mass, and the plasma frequency. The experimental and calculated results for the pressure dependence of ω(p) are both close to dlnω2 / dlnV=-1.9. This agreement suggests that measurements of the electrical resistance as a function of temperature and pressure provide a new test of band-structure calculations. From our measurements of the resistance and calculations of ω(p) and from published results for the compressibility we obtain the pressure dependence of the electron-phonon interaction λ(p). With p given in gigapascals, the result is dlnλ / dp=-0.0047.
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