Thermogravimetric study on HgBa2Can−1CunO2(n+1)+δ (n = 1, 2, 3) superconductors at various oxygen partial pressures

Abstract The oxygen non-stoichiometry of HgBa 2 Ca n −1 Cu n O 2( n +1)+ δ (Hg-12( n −1) n , n = 1, 2, 3) superconductors was studied by thermogravimetric analysis (TGA) in a flowing gas atmosphere with various partial pressures of oxygen ranging from 10 −5 to 10 atm. In 1 atm oxygen, irreversible reactions, probably corresponding to vaporization of Hg, were observed above about 420, 480 and 510°C for Hg-1201, 1212 and 1223 samples, respectively. Reversible reactions with oxygen absorption and desorption were confirmed below these temperatures. By controlling the oxygen partial pressure during the heating process up to 300°C and a subsequent cooling process, we obtained Hg-12( n − 1) n samples with various oxygen contents. The superconducting properties of these samples were also studied. It was found that the oxygen non-stoichiometry of Hg-12( n − 1) n superconductors is very sensitive to the oxidizing atmosphere when they are annealed, even below 300°C.