Mechanism of Oxygenation of HgnBa2Cu3+n+x

We prepared pure Hg1201 with some deficiency in Hg (n=0.96-0.97) and x=0.030 - 0.034 by the reaction of dry oxides in the 121 ratio in an ampoule. At 1 atm O2 oxygenation the deficiency of Hg in the sample increases, but in the 1201 phase it remains nearly constant due to the decrease of the phase content through BaO2 formation. The content of peroxide (determined by calibrated X- ray powder diffraction and Rietveld calculations increases with the temperature of oxygenation. No other impurities (up to 620 degree Celsius were detected. Thus, the Cu content is > 1 in the phase (this was also confirmed by Rietveld. The equation of the reaction is: HgnBa2CuO3+n+x+ 0.5 (z - 0.5zw + m + w - n - x)O2 = (n - m)Hg + z BaO2 + (1 - 0.5z)Hgm/(1-0.5z) Ba2Cu1/(10.5z)O2+((1+m)(1-0.5z)+w. The Cu and oxygen contents x and w were determined by iodometric microtitration. The presence of peroxide requires, in addition to the usual titrations of type A and B, further titration after the decomposition of the peroxide by KMnO4 and the decomposition of the excess of KMnO4 by heating with HCI. The oxygen and Cu contents in YBCO, determined in the mixture of YBCO and BaO2 (up to 0.06 BaO2 per 1 Cu), were in good agreement with those determined without BO2. The Hg content, found by the recalculation of the Cu content, was close to that obtained from Rietveld. The superconductive transitions were sharp and single (only for the first sample a small step on theχ' vs T graph was observed). dTc/dV = 340 was obtained from Tc vs w graph (V a= 2 + 2w is the average copper valence). It is near to the values of 370-460 for the tetragonal 123 superconductors CLBCO. In the table: t degree Celsius temperature of oxygenation, ρ is in mΩ.cm, S - thermopower at 290-295K, μV/K; subscript k - for magnetic susceptibility