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Generating experimental results: high temperature superconductors

As an example of a predominantly experimental publication, we consider [Ihara et al, 1997]. This short publication is one of hundreds of contributions to the proceedings of the International Conference on Materials and Mechanisms of Superconductivity, which are published as six special volumes of the journal Physica C. These contributions may not exceed two pages, which often leads to very cramped publications. A telling example is that, to save room, authors in many cases even abbreviate the list of references by only mentioning the first author of cited articles. In an electronic environment, there is no need for this draconian page limit.

The subject of research in this domain is superconductivity. In 1911, it was discovered that at very low temperatures certain materials do not have any electrical resistance, which implies that an electrical current can run through them unimpeded. The main purpose of research in this domain is to find a material that is superconducting at temperatures that can easily be reached outside a laboratory, so that the material can be applied in everyday life. The temperature below which the material is superconducting is called the critical temperature ${\rm T_c}$. A good superconductor not only has a high critical temperature, but it also satisfies some other requirements, e.g. it should remain in the superconducting state in high magnetic fields and be easy to make. There are no theoretical rules for determining what type of material will be a good superconductor. Therefore, the search is predominantly experimental: based on intuition, trial and error, samples of materials are prepared and studied. The accumulated results of work in this area could be presented in the format of a `catalogue' of superconducting materials.

[Ihara et al, 1997] consists of the sections 1.Introduction, 2.Experimental and Results and discussion, which may be recast into the following modules.

Positioning
  The central question addressed in this publication is whether the critical temperature of the compound ${\rm CuBa_2Ca_3Cu_4O_{12-y}}$, which is abbreviated as Cu-1234, can be increased by doping it with Tl, Hg, Pb, Bi, Au, Ag, C, N, S or another element (i.e. by replacing some of the Cu atoms in the sample with atoms of another type). In addition, the authors search for a preparation method at lower pressures. This information may be presented in a module Central problem .

The reason why the authors consider this compound can be presented in a  Situation module: they have found in previous work that Cu-1234 will be a promising superconductor if its critical temperature can be increased and if it can be synthesised at low pressure.

Methods
  Roughly speaking, the experimental methods concern the preparation and the characterisation of the sample. The sample preparation is described very briefly in section 2.Experimental. In section 3.Results and discussion, additional details are given. In a modular, electronic environment, the editors could instruct authors to provide all information necessary for others to repeat the sample preparation in a module Experimental methods .

The characterisation of the sample, firstly, involves the determination of the structure of the sample by an x-ray diffraction analysis and of its composition by an energy disperse x-ray analysis. The characterisation, secondly, involves the determination of the critical temperature ${\rm T_c}$, by electrical resistivity and magnetisation measurements left unspecified, and the determination of the anisotropy based on the measurement of the magnetic susceptibility of a powder sample and a straightforward calculation. No details are given about these analyses or the apparatus used to perform the measurements. In a modular environment, these details could be made available by means of a link to a mesoscopic or macroscopic module published elsewhere, for instance by the manufacturers of the apparatus.

Results
  Measurements have been performed for samples with various types of doping. Only the results with Tl are given in the original publication, because only the sample
${\rm Cu_{1-x}Tl_xBa_2Ca_3Cu_4O_{12-y}}$ allows for an improvement. If that would be of interest to specific readers, the complete results could in a modular, electronic environment be given in a cluster module Results consisting of constituent modules, each concentrating on a different type of sample.

The x-ray diffraction patterns of the samples form raw data. The data sets can be given in a module Raw data, accompanied by the visualisation in the figure shown in the original publication. By comparing these patterns with patterns stored in a database, using existing software, the structure of the sample can be determined; that structure can be represented in a module Treated results. The techniques for this data treatment are not mentioned in the original publication. In a modular version, they may be made explicit by means of a link to a mesoscopic Numerical methods module. Other raw data are generated in, for example, the measurement of the resistivity at different temperatures. The treated results derived from those data are the values for the critical temperature and anisotropy for the samples.

In a modular environment, the Results module would be the core module of this publication, rather than a module Interpretation . Although there is some discussion about the results (for example, the structure of the sample ${\rm Cu_{0.5}Tl_{0.5}}$-1234 is briefly compared with that of the `parent materials' Cu-1234 and Tl-1234), this discussion does not warrant the creation of a separate Interpretation module.

Outcome
  The main result presented in this publication is the fact that the samples ${\rm Cu_{1-x}Tl_x}$-1234 (with x=0.4 to 0.5) show a superconducting anisotropy of ${\rm\gamma = 4}$ and a critical temperature of 126 K, which is higher than that of the `parent' materials Cu-1234 and Tl-1234. In a modular environment, it may be summarised in a module Findings.


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Next: The development of new Up: Appendix: modularisation in other Previous: Appendix: modularisation in other