Interdisciplinary Materials Research Program Semiannual Progress Report, 1 Mar. - 31 Aug. 1967

Materials science research on inorganic nonmetallic materials, metallic solids, polymers, and solid state physic

Research in materials, science and engineering Annual report 1965-1966

Research projects in materials engineering and science, and solid state, plasma, and low temperature physic

An evaluation of absorption spectroscopy to monitor YBa₂Cu₃O₇₋[x] precursors for metal organics chemical vapor deposition processing

Absorption spectroscopy was evaluated as a technique to monitor the metal organic chemical vapor deposition (MOCVD) process for forming YBa2Cu3O7-x superconducting coated conductors.Specifically, this study analyzed the feasibility of using absorption spectroscopy to monitor the MOCVD supply vapOr concentrations of the organic ligand 2,2,6,6-tetramethyl-3,5-heptanedionate (TMHD) metal chelates of barium, copper, and yttrium.Ba(TMHD)2, Cu(TMHD)2, and Y(TMHD)3 compounds have successfully been vaporized in the MOCVD processing technique to form high temperature superconducting coated conductors, a promising technology for wire fabrication.The absorption study of the barium, copper, and yttrium (TMHD) precursors was conducted in the ultraviolet wavelength region from 200nm to 400nm. To simulate theMOCVD precursor flows the Ba(TMHD)2, Cu(TMHD)2, and Y(TMHD)3 complexes were vaporized at vacuum pressures of (0.03-10)Torr. Spectral absorption scans of each precursor were conducted to examine potential measurement wavelengths for determining vapor concentrations of each precursor via Beer\u27s law.The experimental results show that under vacuum conditions the barium, copper,and yttrium (TMHD) precursors begin to vaporize between 90°C and 135°C, which are considerably lower vaporization temperatures than atmospheric thermal gravimetric analysis indicate. Additionally, complete vaporization of the copper and yttrium (TMHD)precursors occurred during rapid heating at temperatures between 145°C and 195°C and after heating at constant temperatures between 90°C and 125°C for approximately one hour,whereas the Ba(TMHD)2 precursor did not completely vaporize. At constant temperatures,near constant vaporization levels for each precursor were observed for extended periods of time. Detailed spectroscopic scans at stable vaporization conditions were conducted

Materials sciences research

Research projects involving materials research conducted by various international test facilities are reported. Much of the materials research is classified in the following areas: (1) acousto-optic, acousto-electric, and ultrasonic research, (2) research for elucidating transport phenomena in well characterized oxides, (3) research in semiconductor materials and semiconductor devices, (4) the study of interfaces and interfacial phenomena, and (5) materials research relevant to natural resources. Descriptions of the individual research programs are listed alphabetically by the name of the author and show all personnel involved, resulting publications, and associated meeting speeches

Electron-lattice interaction and its impact on high Tc superconductivity

In this Colloquium, the main features of the electron-lattice interaction are discussed and high values of the critical temperature up to room temperature could be provided. While the issue of the mechanism of superconductivity in the high Tc cuprates continues to be controversial, one can state that there have been many experimental results demonstrating that the lattice makes a strong impact on the pairing of electrons. The polaronic nature of the carriers is also a manifestation of strong electron-lattice interaction. One can propose an experiment that allows an unambiguous determination of the intermediate boson (phonon, magnon, exciton, etc.) which provides the pairing. The electron-lattice interaction increases for nanosystems, and this is due to an effective increase in the density of states

The pseudogap in high-temperature superconductors: an experimental survey

We present an experimental review of the nature of the pseudogap in the cuprate superconductors. Evidence from various experimental techniques points to a common phenomenology. The pseudogap is seen in all high temperature superconductors and there is general agreement on the temperature and doping range where it exists. It is also becoming clear that the superconducting gap emerges from the normal state pseudogap. The d-wave nature of the order parameter holds for both the superconducting gap and the pseudogap. Although an extensive body of evidence is reviewed, a consensus on the origin of the pseudogap is as lacking as it is for the mechanism underlying high temperature superconductivity.Comment: review article, 54 pages, 50 figure