The concentrations of paramagnetic centers in Cu3Ba2YO7-d were determined as a function of δ. The concentration of the centers increased with increasing δ but, contrary to the common expectation that any such increase would be comparable to the increase in the concentration of O vacancies, it was some 2 orders of magnitude smaller. A new expression for the specific heat, which took account of the presence of spin-2 as well as spin-½ paramagnetic centers, accurately described the experimental data.

Specific Heat of YBa2Cu3O7-δ: Concentrations of Paramagnetic Centers and Values of Other Parameters as Functions of δ. J.P.Emerson, D.A.Wright, B.F.Woodfield, J.E.Gordon, R.A.Fisher, N.E.Phillips: Physical Review Letters, 1999, 83[7], 1546-9