The Characterization of Cryogenic Materials by X-Ray Absorption Methods
X-ray absorption techniques have in recent years been developed into powerful probes of the electronic and structural properties of materials difficult to study by other techniques. In particular, the extended x-ray absorption fine structure (EXAFS) technique can be applied to a variety of cryogenic materials. Three examples will be used to demonstrate the power of the technique. The first is the determination of the lattice location of dilute alloying additions such as Ta and Zr in Nb3Sn. The Ta additions are shown to reside predominately in Nb lattice sites, while Zr is not uniquely located at either Nb or Sn sites. In addition to structural information, temperature dependent EXAFS studies can be used to determine the rms deviations of atomic bond lengths, providing information about the temperature dependence of interatomic force constants. For Nb3Sn deviations are found from simple harmonic behavior at low temperatures which indicate a softening of the Nb-Sn bond strength. The final example is the study of interfacial properties in thin film systems. This is accomplished by making x-ray absorption measurements under conditions of total external reflection of the incident x-rays. As some examples will show this technique has great potential for studying interfacial reactions, a process used in the fabrication of many superconducting materials.
KeywordsTotal External Reflection Cryogenic Material Atomic Bond Length Bronze Process Ternary Molybdenum Chalcogenide
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- 1.E. A. Stern and S. M. Heald, Basic principles and applications of EXAFS, in: “Handbook on Synchrotron Radiation,” E. E. Koch, ed., North Holland, Amsterdam (1983), pp. 955–1014.Google Scholar
- 2.“EXAFS Spectroscopy,” B. K. Teo and D. C. Joy, eds., Plenum, New York (1981).Google Scholar
- 3.“EXAFS and Near Edge Structure,” A. Bianconi, L. Incoccia, and S. Stipcich, eds., Springer-Verlag, Berlin (1983).Google Scholar
- 4.“Synchrotron Radiation Research,” H. Winick and S. Doniach, eds., Plenum, New York (1980).Google Scholar
- 7.M. Suenaga, D. O. Welch, R. L. Sabatini, O. F. Kämmerer, and S. Okuda, Superconducting critical temperatures, critical magnetic fields, lattice parameters, and chemical compositions of “bulk” pure and alloyed Nb3Sn produced by the bronze process, to be published.Google Scholar
- 9.M. Suenaga, K. Aihara, K. Kaiho, and T. S. Luhman, Superconducting properties of (Nb,Ta)3Sn wires fabricated by the bronze process, Adv. in Cryogenic Engineering-Materials 26:442 (1980).Google Scholar
- 12.K. R. Keller and J. J. Hanak, Ultrasonic measurements in singlecrystal Nb3Sn. Phys. Rev. 154:629 (1967).Google Scholar