Yttrium and Lead NMR Investigation of a 1212 Superconductor (Pb_(1+x)/2Cu(_1-x)/2Sr₂Y_1-xCa_xCu₂O_{7+ d}

We present NMR experiments on the normal state of the 1212 superconductor Pb(1+x/2)Cu(1-x/2)Sr2Y1-xCaxCu2O7+delta: the samples have x-values ranging from 0.2 to 0.5, and most samples have delta-values of zero but there is one sample with a delta-value of 0.1. The bulk magnetic susceptibility for all of the samples presents a temperature variation which can be fitted by the sum of a Curie-Weiss and a Pauli, temperature-independent, term. The Y-89 shift and relaxation data are compared to those from the thallium 1212 superconductor, and to those from YBCO, showing a correlation between the shifts and the distances between the yttrium nuclei and the copper oxide planes. We find an unusual dimerization of the yttrium nuclei, strongly temperature dependent, revealed by Meiboom-Gill spin-echo measurements. The Pb-207 resonance at room temperature exhibits a significant shift as the x-value (the calcium concentration) is varied, possibly indicating a monotonic variation of the Pb valence.