Thermal conductivity and thermoelectric power of high-quality YBa2Cu3O7-delta crystals

The thermal conductivity kappa, and thermoelectric power S, curves as a fun ction of temperature and applied magnetic fields have been presented for th e two principal orientations of a large, high-quality, flux grown, twinned YBa2Cu3O7-delta (Y123) crystal having an oxygen content of 6.95 +/- 0.02. T he overall shape of the kappa (ab), kappa (c), and S-ab, S-c curves, includ ing their general behaviour with magnetic fields, were very similar to thos e previously reported for Y123 crystals. However, the absolute value of the kappa (ab) curve above T-c was significantly larger than that previously f ound even though the peak value at similar toT(c)/2 was comparable with oth er high-quality Y123 crystal results. The absolute value of the kappa (c) c urve was similar to that previously reported for Y123 crystals, showed a co ntinuous increase of conductivity with temperature and there was the hint o f a peak below T-c but no inflection point at T-c. The application of magne tic fields always decreases the value of the kappa (ab) curve below T-c and that of the kappa (c) curve below 120 K. The resistivity of the crystal ov er the same temperature range studied was also determined and the data used to discuss the electron and phonon contributions to the total thermal cond uctivity in the normal state. The S-ab curve showed a change in sign for th e 'foot' region of this overdoped crystal, which is considered significant. (C) 2001 Elsevier Science B.V. All rights reserved.