Temperature Dependence of the NQR Frequency and Linewidth of the High-Jc Superconductor YBa

For Y B a 2 C u 3 0 7 _ a powder samples of different average grain sizes the temperature dependences of 6 Cu NQR frequencies and signal intensities are reported for the Cu (1) site in a temperature range of 4 300 K. Both quantities show a non-monotonic behaviour in the vicinity of the superconduction transition temperature Tc. In the superconducting state the line shape of the NQR signal in zero-field depends on the strength of the dc magnetic field applied during the cooling-procedure. The resulting linewidth yields information about the internal trapped magnetic field.