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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 12 (1990), S. 685-701 
    ISSN: 0392-6737
    Keywords: Kinetic and transport theory ; Classical, semiclassical, quantum theories of liquid structure ; Studies of specific liquid structures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Negli ultimi due decenni la tecnica di diffrazione neutronica di sostituzione isotopica è stata applicata a un grande numero di studi strutturali di sali fusi. Il metodo di analisi sviluppato recentemente della simulazione di Monte Carlo inversa offre un modo di usare quantitativamente tutte le informazioni disponibili per elaborare modelli a tre dimensioni della struttura liquida. Ciò mostra che l'analisi qualitativa basata su posizioni di picco e numeri di coordinazione da funzioni di distribuzione radiali parziali può essere deviante. La sostituzione isotopica è stata applicata solo a studi dinamici negli ultimi cinque anni e poi qualitativamente e al primo ordine. Comunque ciò ha permesso la determinazione di variabili appropriate con le quali si possono descrivere modi collettivi di moto. In un recente e unico esperimento su NiI2 fuso la sostituzione di terz'ordine è stata usata per separare quantitativamente tutti i fattori di struttura dinamici parziali. Questi dati forniranno un test estremamente stringente per ogni descrizione teorica della stato fuso.
    Abstract: Резюме В последние два десятилетия методика дифракции нейтронов широко применялась для структурных исследований расплавленных солей. Недавно развитый подход к моделированию по метолу Монте-Карло позволяет количественно, используя всю имеющуюся информацию, построить трехмерные модели структуры жидкости. Изотопическое замещение применяется к динамическим исследованиям только последние пять лет. Однако, этот подход позволяет определить соответствующие величины, которые описывают коллективные моды движения. В недавнем уникальном эксперименте на расплавленной соли NiI2 была использована замена третьего порядка, чтобы количественно разделить все парциальные динамические структурные факторы. Такие данные обеспечивают строгую проверку для любого теоретического описания расплавленного состояния.
    Notes: Summary Over the past two decades the neutron diffraction technique of isotopic substitution has been applied to a large number of structural studies of molten salts. The recently developed analysis method of reverse Monte Carlo simulation offers a way of quantitatively using all the available information to build three-dimensional models of the liquid structure. This shows that qualitative analysis based on peak positions and coordination numbers from partial radial distribution functions can be misleading. Isotopic substitution has only been applied to dynamical studies within the past five years, and then qualitatively and to first order. However, this has enabled the determination of appropriate variables with which to describe collective modes of motion. In a recent unique experiment on molten NiI2 third-order substitution has been used to quantitatively separate all of the partial dynamical structure factors. Such data will provide an extremely severe test of any theoretical description of the molten state.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Materials Research 22 (1992), S. 217-242 
    ISSN: 0084-6600
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2093-2095 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High- and low-temperature resistance measurements have been carried out on Bi2Sr2CaCu2O8+y and YBa2Cu3O7−x in air and in vacuum. Both the ceramics exhibit a significant change in oxygen content during annealing between 350 and 450 °C. The Bi2Sr2CaCu2O8+y sample exhibits an increase in resistance with increased oxygen content resulting in deterioration of superconductivity, whereas YBa2Cu3O7−x shows improvement in superconducting behavior with increase in oxygen content. Consequently Bi2Sr2CaCu2O8+y prepared by fast cooling from the sintering temperature possesses a higher Tc , whereas slow cooling of YBa2Cu3O7−x produces a higher Tc .
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 393-398 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A large single-crystal of α-AgI was grown in situ from the melt on the SXD single-crystal neutron time-of-flight Laue diffractometer using a specially designed furnace. A wide range of reciprocal space was accessed with minimal rotation of the arbitrarily aligned sample. Weak rings of diffuse scattering were observed together with strong scattering around some Bragg peaks. The results are discussed with reference to earlier powder diffraction data and indicate significant correlations between the motion of the silver ions and the vibrations of the iodide ions.
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  • 5
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 29 (1996), S. 285-290 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A Monte Carlo algorithm for the analysis of powder diffraction patterns is presented. One aim of this algorithm, which can be used as a supplement to the regular Rietveld refinement, is to provide a self-consistent determination of the thermal displacements of the atoms. This is achieved by modelling the total scattered intensity, comprising both the Bragg peak intensity and the diffuse contribution to the spectrum from the scattering density of an assembly of atoms. This assembly, which is constructed by the reverse Monte Carlo technique so as to yield a best fit with the data, is then used to calculate the average atomic thermal displacements. This allows for a refinement that, in principle, no longer requires angle-dependent background parameters, and that is well suited for dealing with highly anisotropic Debye–Waller factors and split atomic sites.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 51 (1995), S. 763-771 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The scattering from crystals has two components, Bragg and diffuse. In the case of disordered crystalline materials, or those at high temperature, the latter contribution is considerable and contains a great deal of information about any static or thermal disorder in the system. However, interpretation of this diffuse scattering is in general difficult. A new and widely applicable technique for modelling single-crystal diffuse scattering has been developed, which is most useful for the study of disordered crystalline materials. The algorithm, based on the reverse Monte Carlo method, is described in detail, and the information that can be obtained using it is discussed with reference to a study on ice Ih.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 783-789 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new reverse Monte Carlo (RMC) method for modelling both lattice and magnetic disorder in powder crystalline materials by direct calculation of the structure factor has been developed. The method, the program and the basic theory are described in some detail. Initial results from modelling the lattice and magnetic structure of MnO around the Néel temperature are also presented.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 344 (1990), S. 423-425 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 62 (1985), S. 15-19 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have determined partial radial distribution functions describing the distribution of ions around anions and around cations in α-AgI at 573 K by measuring the diffuse neutron scattering and using the method of isotopic substitution on the silver ions. The results show that it is necessary to consider all three partial diffuse structure factors (A ++,A +−, andA −−) and not just two (A ++ andA +−) as has been done previously. The pair distribution functions show that the short range order in displacements of ions from the lattice sites appears remarkably similar to the short range order in molten CuCl. Of particular note is the similarity of the Ag−Ag and the Cu−Cu correlations which show very little structure.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Ionics 1 (1995), S. 153-158 
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract For the first time neutron diffraction, X-ray diffraction and EXAFS data have been combined simultaneously using the RMC method to model the fast-ion conducting glass, (AgI)x(AgPO3)1−x. This material is of considerable technological and scientific interest due to its high ionic conductivity at ambient temperature. We present some details of the RMC technique and highlight some of the structural information obtained from our models. The origin of the “first sharp diffraction peak” in the neutron diffraction data is explained, about which there has been considerable speculation. Diffusion pathways for ionic conduction are observed. A simple analysis of available free volume shows that a percolation transition in the ionic conductivity occurs between x=0.2 and 0.3, in agreement with a prediction based on conductivity measurements. This study highlights the considerable power that these developments of the RMC method have for the structural modelling of complex amorphous materials.
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