Determination of the oxidizing ability of HTSC materials containing two elements with a variable degree of oxidation

Abstract

The presence of mixed valence states of elements is supposed to be a common characteristic feature of the high-Tc superconductors, based on copper oxides. Methods have been suggested for the determination of Cu(llI) in the Y-Ba-Cu-O ceramics and separate determination of two oxidants: Bi(V) and Cu(llI), TI(IlI) and Cu(llI) in the corresponding materials. Compounds of Bi(V) oxidize in the ions of Mn(II) to MnO2 in the acidic medium. Active oxygen, bound to Cu(Ill) is isolated, not oxidizing Mn(ll). MnO,~ is titrated then with a solution of Felll) sulphate. For the determination of TI(III) the sample is dissolved in the acid, Cu(III) is reduced to Cu(ll) and TI(III) is titrated with the hydroquinone solution. The compounds of Bi(V), TI(IIIt and Cu(lll), having high oxidation-reduction potentials can oxidize the complex Co(II)-EDTA to Co(III)-EDTA. The colour intensity of the latter is proportional to the content of Cu(Ill) or to the sum of Bi(V) and Cu(llI) or TI(III) and Cu(llIt. The content of Cu(III) in Bi-and Tl-containing materials is determined by the difference.