Techniques for obtaining far infrared transmission spectra of high Tc, superconductors and related synthetic precursors
✍ Scribed by H.D Bist; H Ning; T Datta; T.S Little; J.R Durig
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 439 KB
- Volume
- 50
- Category
- Article
- ISSN
- 1386-1425
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✦ Synopsis
The far infrared (FT-IR) spectra of Y203, CuO, BaO,, YBa$uJ07_6 and Tl,Ca,Ba,Cu,O,,, have been recorded in the range of 350-60 cm-'. A variety of sample handling techniques have been utilized which include dispersion of the samples in nujol and fluorolube. Additionally, we present preliminary results of a technique of preparing thin films (l-20pm thick) of these materials. These films do not require a substrate but are dispersed in a polyethylene matrix fused between two polyethylene plates. Such films are suitable for optical applications.
VIBRATIONAL SPECTROSCOPY, both IR and Raman data, of the recently discovered superconductors of the general formula MBa2Cu307_d (M = Y or any rare earth) can be used to investigate the extent of the electron-phonon coupling mechanism in the production of high superconducting transition temperatures. These techniques can also provide a means of estimating the gap energy. The utility of vibrational spectroscopy for the investigation of high temperture superconducting materials has already been demonstrated [l, 21. These studies have provided information about the low-lying phonon frequencies, other elementary excitations and electronic band structure. For some of the earliest discovered materials of this type reliable studies of the vibrational spectra have been provided on high quality crystals, but results need to be made available on the more recently discovered materials and on the thin films deposited on a variety of substrates.
From some of the initial studies of these materials, variations in the reported data exist and are the result of the presence of "impurities". Such "impurities" occur in the form of additional parasitic phases, variations in the oxygen content, twin and grain boundaries, defects, voids, imperfections, irregularities in the structure, etc. and may drastically affect the superconductors. The utilization of different sample handling techniques and extent of exposure of the surface of the materials to atmospheric water and carbon dioxide could also be sources of variations in the reported data. Other sources include crystal orientation or sample heterogeneity [l, 21. Regardless of the sources of the discrepancies and before these data can be interpreted with any certainty, additional analytical techniques should be developed and applied to the study of these materials and their synthetic precursors.
The far IR reflectance [3] and transmission [4] spectra of YBa,Cu,O,_b have been reported. The differences between spectra are at least partly due to the physical and optical effects produced by the restricted (micron sized) dimension of the sample. The latter can affect light propagation [5] and result in structural resonance [6], as well as produce quantum effects in metallic particles [7] and quantum wells [8]. Thus, it is not only possible to obtain the vibrational and electronic excitations of the superconductors and their synthetic precursors, but also to deduce information regarding the effects of small dimensions from a detailed analysis of the spectra. Presently, we will report the