Effects of carbon incorporation on the doping state of YBa 2 Cu 3 O y (Y-123) were investigated.Quantitative carbon analysis revealed that carbon could be introduced into Y-123 from both the precursor and the sintering gas. Nearly carbon-free (< 200 ppm) samples were prepared from a vacuum-treated precursor by sintered at 900 ˚C and cooling with 20 ˚C /min in flowing oxygen gas. The lower T c (= 88 K) and higher oxygen content (y = 6.98) strongly suggested the overdoping state, which was supported by the temperature dependence of resisitivity and thermoelectric power. The nuclear quadrapole resonance spectra and the Raman scattering spectra indicated that there was almost no oxygen defect in the Cu-O chain in these samples.On the other hand, in the same cooling condition, the samples sintered in air stayed at optimal doping level with T c = 93 K, and the intentionally carbon-doped sample was in the underdoping state. It is revealed that about 60% of incorporated carbon was substituted for Cu at the chain site in the form of CO 3 2+ , and the rest remains at the grain boundary as carbonate impurities. Such incorporation affected the oxygen absorption process in Y-123. It turned out that the oxygen content in Y-123 cannot be controlled only by the annealing temperature and the oxygen partial pressure but also by the incorporated carbon concentration.

No abstract

No abstract

We succeeded in obtaining amorphous SiGe thin films containing ³6 nm nanocrystals by means of a vapor deposition. The thermal conductivity was controllable using the particle size of the nanocrystals, and a very small value of thermal conductivity ³1 W/mK was obtained with an averaged particle size less than 6 nm. The electron transport properties were improved using Au-doping to form impurity levels near the valence band top, and B-doping to control the Fermi level. With the effect of this co-doping technique and nano-structuring, we estimated obtaining ZT = 1.38 at 1100 K.