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The discovery of the superconducting material Y1Ba2Cu3O6+δ ( “123” material) resulted in a world wide interest in the pseudo-ternary system BaO·YO·CuO. A complete study of the phases present in this system was initiated to develop a better understanding and processing of the superconducting 123 material. The crystal structures were established for two of the three ternary compounds in this system immediately after the discovery of superconductivity. One such phase was a green insulating compound Y2Ba1Cu1O5 (”211”) which has the space group. The superconducting 123 compound was found to have the space group Pmmm and an ordered triple-celled perovskite structure.
Mg-doped GaN films grown by metalorganic chemical vapor deposition were characterized by variable-temperature Hall-effect measurements and Fourier-transform infrared absorption spectroscopy. As-grown, thermally activated, and deuterated Mg-doped GaN samples were investigated. The existence of Mg-H complexes in GaN is demonstrated with the observation of a local vibrational mode (LVM) at 3125 cm-1 (8 K). At 300 K this absorption line shifts to 3122 cm-1. The intensity of the LVM line is strongest in absorption spectra of as-grown GaN. Mg which is semi-insulating. Upon thermal activation, the intensity of the LVM line significantly decreases and an acceptor concentration of 2×1019cm-3 is derived from the Hall-effect data. After deuteration at 600°C the resistivity of the Mg-doped GaN increased by four orders of magnitude. A LVM line at 2321 cm-1 (8 K) appears in the absorption spectra which is consistent with the isotopie shift of the vibrational frequency when D is substituted for H.
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