Journal of Physics F: Metal Physics最新文献

{"title":"Fermi surfaces in Nb3Sn through positron annihilation","authors":"L. Hoffmann, Ashutosh Kumar Singh, H. Takei, N. Toyota","doi":"10.1088/0305-4608/18/12/011","DOIUrl":"https://doi.org/10.1088/0305-4608/18/12/011","url":null,"abstract":"In order to understand superconductivity in A15 structure compounds, two-dimensional angular correlation of positron annihilation radiation (2D-ACPAR) has been measured in a single crystal of Nb3Sn for three orientations (100), (110) and (210). Also band-structure calculations using the self-consistent linear muffin-tin orbital (LMTO) method are performed for Nb3Sn. A comparison between experiment and theory at different stages of the analysis shows in general good agreement. The measured momentum distributions are folded to the crystal momentum space, followed by a three-dimensional reconstruction of the occupation density. The extracted Fermi surfaces (FS) reveal the presence of a cube-shaped hole pocket, responsible for the high superconducting transition temperature (Tc=18 K), which seems to be a feature of all FS of high-Tc A15 compounds.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"15 1","pages":"2605-2616"},"PeriodicalIF":0.0,"publicationDate":"1988-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80225813","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The heat capacity of high-purity dysprosium from 0.5 to 20 K","authors":"R. W. Hill, K. Gschneidner","doi":"10.1088/0305-4608/18/12/006","DOIUrl":"https://doi.org/10.1088/0305-4608/18/12/006","url":null,"abstract":"Measurements have been made on a two single-crystal specimens of high purity dysprosium. After heat treatment to remove hydrogen, the specimens give identical results. Analysis shows that there may still be small (1%) effects due to hydrogen, and this is the main cause of uncertainty in the deduced values of the electronic specific heat coefficient gamma =4.9+or-0.1 mJ K-2 mol-1 and the Debye temperature in the low temperature limit theta 0=192+or-2 K. At the higher temperatures the magnetic contribution accounts for about half the total specific heat, and its temperature dependence can be represented by an expression of the form AT\" exp(-Eg/kT). For n=1.5 it is found that Eg=26 K, but other pairs of n and Eg fit equally well.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"22 1","pages":"2545-2557"},"PeriodicalIF":0.0,"publicationDate":"1988-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85935293","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrogen mobility parameters and dislocation pinning rates at very low temperatures in tantalum","authors":"J. Lauzier, J. Hillairet, A. Vieux-Champagne, H. Schultz","doi":"10.1088/0305-4608/18/12/005","DOIUrl":"https://doi.org/10.1088/0305-4608/18/12/005","url":null,"abstract":"Pinning rates of dislocations by hydrogen and deuterium have been analysed in monocrystalline tantalum samples of ultrahigh purity. For this purpose, measurements of internal friction and elastic modulus were performed down to 2 K, using a vibrating strip system. A marked pinning stage located between 8 K and 11 K was revealed for hydrogen. The authors show that it reflects the arrival of the hydrogen atoms at dislocation sites, resulting in the pinning of the dislocation kinks. The inferred jump rate of hydrogen atoms is 3*102+or-1 s-1 at 8.3 K. The temperature dependence of diffusion was found to obey a power law, with a large exponent, 15+or-3. Deuterium migration was also detected, at around 14 K. The results obtained are compared with previous data at higher or similar temperatures and discussed in relation to the existing theories for quantum diffusion.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"48 1","pages":"2529-2544"},"PeriodicalIF":0.0,"publicationDate":"1988-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84682137","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Direct evidence of two different relaxation processes induced by heat treatment on Fe40Ni40B20 glassy ribbons","authors":"M. Clavaguera-Mora, M. D. Baró, S. Suriñach, N. Clavaguera, J. Parellada, D. Crespo, T. Pradell","doi":"10.1088/0305-4608/18/12/017","DOIUrl":"https://doi.org/10.1088/0305-4608/18/12/017","url":null,"abstract":"The effect of heat treatment on Fe40Ni40B20 glassy ribbons (V0040) has been studied by differential scanning calorimetry, X-ray diffraction, TEM and Mossbauer spectroscopy. Mossbauer data were fitted considering the asymmetry of the lines using an appropriate model (that of Brand et al.). Calorimetrically there are two effects, one exothermic and the other endothermic, that can be separated by selective heat treatments of the samples. X-ray diffraction, TEM and Mossbauer spectroscopy do not show any evidence of crystallisation or phase separation. Heat treatments induce changes in long-range order parameters but there is no such evidence on short-range order parameters. The analysis of the set of results provides direct evidence of the existence of two different relaxation mechanisms induced by heat treatment. One of them forces the local magnetisation to be more aligned with the ribbon plane than in the as-quenched glass, while the other randomises it.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"47 1","pages":"2669-2681"},"PeriodicalIF":0.0,"publicationDate":"1988-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77724881","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Non-local positron-electron density functional theory and the positron surface state","authors":"K. O. Jenson, A. Walker","doi":"10.1088/0305-4608/18/12/002","DOIUrl":"https://doi.org/10.1088/0305-4608/18/12/002","url":null,"abstract":"The authors describe a non-local positron-electron density functional theory and show how it can be used to find the correlation potential for a positron in inhomogeneous systems where non-local effects are important. The theory is applied to the image potential induced surface state at a metal surface. Here the image potential arises from interactions between the positron and its screening cloud, which become increasingly long ranged and non-local as the positron leaves the surface. They have tested the theory with calculations of the binding energy and lifetime of a positron at an aluminium surface which agree well with experimental values.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1988-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90205431","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of localised modes on spin fluctuations and transition temperatures of Zr metallic glass superconductors","authors":"S. K. Roy, A. Mondal","doi":"10.1088/0305-4608/18/12/015","DOIUrl":"https://doi.org/10.1088/0305-4608/18/12/015","url":null,"abstract":"The effects of localised phonons on transition temperatures in three binary metallic systems Ni-Zr, Co-Zr and Fe-Zr have been theoretically evaluated from the renormalised electron-phonon parameter and compared with their metallic glass counterparts. The influence of spin fluctuations has also been evaluated within the range 0.50<x<0.71 for Ni-Zr, 0.53<x<0.70 for Co-Zr, and 0.72<x<0.80 for Fe-Zr compounds (x being the concentration of Zr). The results obtained using a modified form of the McMillan equation clearly show the influence of spin fluctuations in reducing the superconducting transition temperatures. The transition temperatures of these binary metallic compounds have been found to be very sensitive to the variations of concentrations of Ni, Co and Fe in Zr, and agree well with the reported values at definite concentrations, indicating a possibility of phase transition in these systems.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"101 1","pages":"2649-2657"},"PeriodicalIF":0.0,"publicationDate":"1988-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89288780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Criticalbehaviour of the planar helical to or from paramagnetic phase transition in dysprosium and holmium","authors":"G. Brits, P. D. Plessis","doi":"10.1088/0305-4608/18/12/016","DOIUrl":"https://doi.org/10.1088/0305-4608/18/12/016","url":null,"abstract":"The planar helical to or from paramagnetic phase transition for Dy is inferred to be of second-order nature from the continuous behaviour of neutron scattering as well as ultrasonic attenuation and velocity measurements. This result is corroborated by the absence of thermal hysteresis at the critical point. Integrated neutron scattering measurements yield a value of the critical exponent beta , which describes the spontaneous sublattice magnetisation, of beta =0.39+or-0.01. Finally, thermal hysteresis was observed for Ho in the ordered region.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"142 1","pages":"2659-2668"},"PeriodicalIF":0.0,"publicationDate":"1988-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81434914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermodynamic properties of liquid Na-Cd and Na-In","authors":"S. Harada, S. Takahashi, S. Takeda, S. Tamaki, P. Gray, N. Cusack","doi":"10.1088/0305-4608/18/12/007","DOIUrl":"https://doi.org/10.1088/0305-4608/18/12/007","url":null,"abstract":"New measurements of the free energy and entropy of mixing and the associated thermodynamic properties of liquid Na-Cd and Na-In alloys are reported. It is inferred that there exists some kind of short-range order of Na, whilst there is a phase separation tendency in the alloys in the Na-rich region. These contradictory features are interpreted in terms of the interchange energies in the alloys which vary as a function of Na concentration.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"25 1","pages":"2559-2567"},"PeriodicalIF":0.0,"publicationDate":"1988-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88147923","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"X-ray diffuse scattering from β'-AgZn alloy","authors":"Y. Matsuo, K. Ohshima, H. Iwasaki, Y. Kuroiwa, H. Maeta, K. Haruna","doi":"10.1088/0305-4608/18/12/003","DOIUrl":"https://doi.org/10.1088/0305-4608/18/12/003","url":null,"abstract":"Measurements were made of X-ray diffuse scattering from quenched AgZn single crystals which are in a metastable beta '-phase state having the B2-type structure. Two notable features were found in the distributions of diffuse scattering intensity: one is intensity streaks running through the fundamental reflection points in the (110) and its equivalent directions and the other is intensity sheets extending uniformly parallel to the (111) and its equivalent reciprocal lattice (REL) planes. The former is the diffuse scattering often observed in the B2 alloys and is associated with the (110) (110) transverse acoustic phonons. The latter shows the presence of random displacements of the (111) atom rows in the (111) direction. The structural relationship between the beta ' and the stable zeta phase suggests that the displacements are a precursive fluctuation of the beta ' to zeta transition, but the temperature dependence of the intensity of the (111) sheets show that they are purely thermal in their origin.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"21 1","pages":"2505-2512"},"PeriodicalIF":0.0,"publicationDate":"1988-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87844843","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The atomic and electronic structure of metallic glasses: search for a structure-induced minimum in the density of states","authors":"J. Hafner, S. Jaswal, M. Tegze, A. Pflugi, J. Krieg, P. Oelhafen, H. Güntherodt","doi":"10.1088/0305-4608/18/12/010","DOIUrl":"https://doi.org/10.1088/0305-4608/18/12/010","url":null,"abstract":"The atomic and electronic structures of amorphous and crystalline Mg-Zn alloys are studied by computer simulation, electronic band-structure calculations and photoemission measurements. The spectra for the metallic glasses and for pure crystalline zinc show a narrow band of Zn 3d states centred at a binding energy EB of about -9.7 eV, overlapping the bottom of a broad sp band. There are indications of a minimum in the electronic density of states at the Fermi level for the glasses and for the pure metals. Molecular dynamics and potential-energy mapping calculations based on pseudopotential-derived interatomic forces are used to construct models for the atomic structure, with no other input than the composition and the atomic numbers and atomic weights of the components. The analysis of these models-which are in reasonable agreement with X-ray and neutron diffraction data-shows that the local topology of the glassy structure is very similar to that of the stable crystalline intermetallic compounds. The glassy structure is best described as a disordered tetrahedral close packing with a weak tendency to chemical short-range order whose precise degree remains to be detailed. The linearised muffin-tin orbital method in the atomic sphere approximation is used to perform self-consistent calculations of the electronic DOS of crystalline Mg and Zn, of the hexagonal Laves phase MgZn2 and of 'amorphous' supercells (each containing 60 atoms) representing glassy MgZn2 and Mg7Zn3 alloys. In each case the authors find a minimum in the DOS at EF, and d bands centred at EB approximately=-7.5 eV. A transition-state calculation shows that the d-band position in the photoemission spectra is shifted relative to the electronic eigenvalue due to self-energy corrections. Photoemission and X-ray emission intensities are calculated from the partial local DOS and the self-consistent potentials in a single-scatterer final-state approximation. The comparison with experimental confirms the validity of the electronic structure calculations. The work represents one of the first ab initio calculations of the atomic and the electronic structure of a metallic glass, and the first confirmation of the existence of a minimum in the electronic DOS at EF. The relevance of the DOS minimum to the structure-potential relationship and to the stability of the glassy phase is discussed.","PeriodicalId":16828,"journal":{"name":"Journal of Physics F: Metal Physics","volume":"1 1","pages":"2583-2604"},"PeriodicalIF":0.0,"publicationDate":"1988-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76096741","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}