Copper nuclear quadrupole resonance (NQR) and zero field nuclear magnetic resonance (ZFNMR) studies of YBa2Cu3O6.5 show that a magnetic phase appears in underdoped 123 superconductors treated in ambient wet air. The studies give convincing evidence that the ``empty'' CuO chains play the role of easy water insertion channels. The reaction occurs first in ordered regions of the crystallites. The final product of the reaction is a non-superconducting antiferromagnetic compound characterized by at least two types of magnetically ordered copper ions with ZFNMR spectra respectively in the frequency ranges of 46-96 and 96-135 MHz respectively. Even for powder samples fixed in an epoxy resin, the reaction is found to occur partly after a few years.
@article{arxiv.cond-mat/9906295,
title = {Antiferromagnetism in hydrated 123 compounds},
author = {A. V. Dooglav and A. V. Egorov and I. R. Mukhamedshin and A. V. Savinkov and H. Alloul and J. Bobroff and W. A. MacFarlane and P. Mendels and G. Collin and N. Blanchard and P. G. Picard},
journal= {arXiv preprint arXiv:cond-mat/9906295},
year = {2009}
}