| 1. |
- Minnhagen, Petter
(författare)
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Aspects on diagrammatic expansion for models related to a homogeneous electron gas
- 1975
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Ingår i: Journal of Physics C: Solid State Physics. - : IOP Publishing. - 0022-3719. ; 8:10, s. 1535-1548
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Tidskriftsartikel (refereegranskat)abstract
- n a previous paper (see abstr. A76748 of 1974) the expansion of the irreducible self-energy of an electron gas was studied and found to give unreliable results for the satellites of the one-electron spectra function. This was due to the incorrect analytic properties of the corresponding green function. These results are confirmed and extended by studying a simple model (s-model) which allows the nature of different approximation schemes to be demonstrated clearly. A consistent iterative expansion method for the green function is also developed, which, in addition to giving a one-electron green function with correct analyticity and a spectral function fulfilling the sum rule, is computationally simple enough to be used for an electron gas and possibly for simple metals. The method gives quite reasonable results for the s-model when developed to second order in the screened interaction. From comparison with other electron gas calculations it is concluded that the method should also give reasonable results for an electron gas.(9 refs)
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| 2. |
- Andersson, Per, et al.
(författare)
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Effect of guest molecule size on the thermal conductivity and heat capacity of clathrate hydrates
- 1983
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics Publishing (IOPP). - 0022-3719. ; 16:8, s. 1423-1432
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Tidskriftsartikel (refereegranskat)abstract
- Using the transient hot-wire method, we have measured both the thermal conductivity, lambda, and the heat capacity per unit volume, rho cp, for structure II clathrate hydrates of 1,3-dioxolane (DO) and cyclobutanone (CB), and compared the results with similar previous measurements for tetrahydrofuran (THF). All three clathrate hydrates showed a glass-like temperature dependence of lambda. The magnitude of lambda was small, about the same as liquid water, and decreased in the sequence DO-THF-CB which corresponds to an increase in the size of the guest molecule. There was some evidence to support the suggestion that the dominant process in the thermal resistivity was associated with excitation of rotational vibrations of the guest molecules. In all cases, the pressure dependence of lambda was unusually small. We found evidence that there was a phase transition on the CB clathrate hydrate (and almost certainly also in the DO clathrate) at 135K and 1 GPa, which are essentially the same conditions under which we previously found an analogous transition for THF. In each case, the resultant presumably metastable phase may be a new type of clathrate hydrate arising from densification of the host structure. For the three clathrates, our results for rho cp did not depend on the nature of the guest species, and at 0.1 GPa, were the same as previously found for ice Ih.
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| 3. |
- Andersson, Per, et al.
(författare)
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The phase diagram of ammonium iodide (NH4I) under pressure, and a comparison with NH4Cl and NH4Br
- 1987
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics (IOP). - 0022-3719. ; 20:29, s. 4737-4743
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Tidskriftsartikel (refereegranskat)abstract
- During recent measurements of thermal conductivity using the transient hot-wire method, data were obtained for pressure-temperature coordinates corresponding to transitions amongst phases I, II, III and IV of NH4I which extended reliable knowledge of the phase diagram to pressures of 2 GPa. Comparison of the phase diagrams of NH4Cl, NH4Br and NH4I showed that a generalised phase diagram covering these substances was a poor approximation if the higher-order critical points or triple points (as appropriate) were made coincident. However, the ferro-ordered-to-disordered phase transition boundaries of these substances could be made to follow a common curve with an alternative empirical adjustment of pressure and temperature. When this was done, the adjustments of temperature required were correlated with differences in barrier height opposing re-orientational motion of the ammonium species.
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| 4. |
- Andersson, Per
(författare)
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Thermal conductivity under pressure and through phase transitions in solid alkali halides : I. Experimental results for KCl, KBr, KI, RbCl, RbBr and RbI
- 1985
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics (IOP). - 0022-3719. ; 18:20, s. 3943-3955
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity, lambda , of polycrystalline KCl, KBr, KI, RbCl, RbBr and RbI has been measured at temperatures (T) from 100-400K at pressures (P) up to about 2.6 GPa, using the transient hot-wire method. Extensive results were obtained for lambda (T,P) of both the low-pressure (NaCl-type) and high-pressure (CsCl-type) phases. There was generally good agreement with previous results for lambda (P) at room temperature, the decrease of lambda through the phase transition and lambda (T) at atmospheric pressure. The heat capacity per unit volume was also measured simultaneously but for technical reasons data could be obtained only near room temperature. Corresponding values of specific heat capacity were in good agreement with previous work over the whole pressure range.
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| 5. |
- Andersson, Per, et al.
(författare)
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Thermal resistivity of ice Ih near the melting point
- 1980
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics Publishing (IOPP). - 0022-3719 .- 1747-3802. ; 13:4, s. L73-L76
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Tidskriftsartikel (refereegranskat)abstract
- The thermal resistivity r(T) of ice Ih has been re-measured from 120K to as close as practicable to melting. Measurements were made under isobaric conditions at a pressure of 0.07 GPa, and corrected to isochoric conditions. The resultant deviation from the simple theoretical prediction, r/T=constant, has been plausibly accounted for by interaction between optic and acoustic phonons. Thermal resistivity arising from the presence of point defects has been shown to be of negligible importance.
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| 6. |
- Andersson, Staffan, et al.
(författare)
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The thermal conductivity and heat capacity of single-crystal Si under hydrostatic pressure
- 1988
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics Publishing (IOPP). - 0022-3719. ; 21:20, s. 3727-3735
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity λ and heat capacity ρcP per unit volume of single-crystal Si have been measured under hydrostatic pressure up to 1 GPa at room temperature. The thermal conductivity was found to increase slightly with increasing pressure. For the volume dependence of λ expressed in terms of the Bridgman parameter g=-( δ(ln λ )/ δ(ln V))T, the authors obtained g=0.4. The specific heat capacity cP, calculated from their measured ρcP, was found to be constant against pressure.
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| 7. |
- Andersson, Staffan, et al.
(författare)
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Thermal conductivity and heat capacity of single-crystal LiF and CaF2 under hydrostatic pressure
- 1987
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics Publishing (IOPP). - 0022-3719. ; 20:35, s. 5951-5962
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity, lambda , and heat capacity per unit volume, rho cp, have been measured under hydrostatic pressure up to 1 GPa at room temperature, using a dynamic two-strip method. The standard deviation of lambda and rho cp was always better than 0.2%. The volume dependence of lambda expressed in terms of the Bridgman parameter, -( delta ln (lambda) / delta ln V)T, was found to be 7.9 for LiF and 9.2 for CaF2. The specific heat capacity, cp, calculated from the measured rho cp, was found to decrease slightly with increasing pressure.
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| 8. |
- Brydsten, Ulf, et al.
(författare)
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Thermal conductivity of single-crystal NaCl under uniaxial compression
- 1983
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics Publishing (IOPP). - 0022-3719. ; 16:1, s. 143-146
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Tidskriftsartikel (refereegranskat)abstract
- The variation of the thermal conductivity of single-crystal NaCl under uniaxial compression is investigated by the dynamic hot-strip method. Over a stress range of 0-1.0 MPa no effect whatsoever is found. The relative change in thermal conductivity under uniaxial compression must be smaller than 1.5*10-9 Pa-1, contrary to the result of an earlier investigation.
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| 9. |
- Fransson, Åke, et al.
(författare)
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Thermal conductivity, heat capacity and phase stability of solid sodium chlorate (NaClO3) under pressure
- 1983
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics Publishing (IOPP). - 0022-3719. ; 16:15, s. 2861-2869
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity, lambda, and the specific heat capacity at constant pressure, cp, have been measured for solid sodium chlorate (NaClO3) in the temperature range 100-300K. Differential scanning calorimetry (DSC) was used to measure cp at atmospheric pressure, whilst the transient hot-wire method was used to measure simultaneously both lambda and the heat capacity per unit volume, rho cp, up to a pressure of 2 GPa. We found that our measured DSC values of cp exceeded those previously predicted from a lattice dynamical model, consistent with a previous prediction of disorder in Cl atom positions at high temperatures. However, such disorder, if it exists, did not affect the transport of heat, since we found that lambda (T) under isochoric conditions appeared to be determined entirely by three-phonon umklapp interactions. We found no evidence for a phase transition in NaClO3 up to 2 GPa at 300K, contrary to some previous results. However, we did observe an explosive chemical instability to occur at about 1 GPa and 130K.
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| 10. |
- Gerlich, David, et al.
(författare)
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Temperature and pressure effects on the thermal conductivity and heat capacity of CsCl, CsBr and CsI
- 1982
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Ingår i: Journal of Physics C: Solid State Physics. - : Institute of Physics (IOP). - 0022-3719. ; 15:25, s. 5211-5222
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity and the heat capacity per unit volume of CsCl, CsBr and CsI have been measured as a function of temperature and pressure over the ranges 100-400 K and 0-2.5 GPa. For CsCl and CsBr most of the contribution to the thermal conductivity comes from acoustical phonons, while in the case of CsI there is an appreciable contribution from optical phonons. The part of the thermal conductivity due to propagating acoustic phonons has essentially a T-1 temperature dependence. The heat capacity is found to be essentially constant over the measured temperature and pressure range for all three materials. The pressure dependence of the Gruneisen constant, derived from the change in the thermal conductivity under pressure, is correlated with the same quantity obtained by other methods, and the reasons for the discrepancies are discussed.
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