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VOLUME 55 (1992) | ISSUE 10 | PAGE 574
Variable valence and ESR of yttrium ceramics
Expressions are derived for the spin susceptability, the width of the ESR line, and the shift of the resonant frequency of paramagnetic ions in a variable-valence state. The theoretical temperature dependence of the parameters of the ESR spectrum of nonsuperconducting phases of ceramic YBa2Cu,Ox agrees with experimental data. It is suggested that, as the oxygen content in YBa2Cu,Ox increases from 6.1, the valence of the copper ions in Cul sites decreases, reaching values S 1.6-1.7 for the superconducting phases of this ceramic. The same effect would explain the sharp decrease in the intensity of the ESR signal in superconducting YBa,Cu ,Ox samples.