Far infrared transmission properties of metallic and insulating granular free standing $\rm YBa\sb2Cu\sb3O\sb{x}$ thin films were measured. Since no substrate was present, we were able to cover a 10-650 cm$\sp{-1}$ frequency range, wider than in any previous transmission measurements on these materials. The films, prepared by a novel technique, were 0.1-1 $\mu$m thick and about 100 mm$\sp2$ in area. This is compared to the 1 mm$\sp2$ area of free standing films made by previous methods. The metallic films showed the superconducting transition below 85 K. All of the films had the stoichiometric composition and the expected polycrystalline lines in the x-ray spectra. / The transmission spectra of the metallic films were measured both in the normal and the superconducting states. These films behaved as a mixture of conducting and insulating small grains in the vicinity of the percolation threshold. The data were modeled by the two-dimensional effective-medium approximation. The calculated frequency-dependent absorption coefficients and the effective conductivities agreed with some previous theoretical studies. This experiment is the first investigation of percolative phenomena in an insulator-high-T$\sb{\rm c}$-superconductor mixture. / We also measured the reflectance spectra of modified Heusler alloys, UNiSn and ThNiSn, at temperatures 10-300 K in the frequency range 10-700 cm$\sp{-1},$ and at room temperature in the range 10-44800 cm$\sp{-1}.$ These are the first measurements on these materials in this frequency range. The reflectance spectra are consistent with the semiconducting behavior of ThNiSn, and the observed metal-semiconducting transition in the UNiSn system at 43 K. Below 42 K UNiSn orders antiferromagnetically, while the isostructural ThNiSn shows no such ordering. Two phonon lines, observed in the UNiSn spectra, split below 42 K, indicating a lattice change. A single phonon line was present in ThNiSn spectra at all temperatures. The dielectric functions and conductivities were calculated from the reflectance spectra using the Kramers-Kronig analysis. Below 42 K we observed an antiferromagnetic mode at 20 cm$\sp{-1}$ in the UNiSn sample. / Source: Dissertation Abstracts International, Volume: 53-07, Section: B, page: 3567. / Major Professor: Hon-Kie Ng. / Thesis (Ph.D.)--The Florida State University, 1992.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_76706 |
| Contributors | Kilibarda-Dalafave, Snezana., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 162 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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