Oxygen in pores and internal friction in high-temperature superconductors
Abstract
It has been shown that in the case of porous (∼ 10%) samples of HTSC compounds (YBa2Cu3Ox and La2−xSrxCuO4) the temperature dependence of the low-frequency internal friction (LFIF) reveal extra peaks caused most likely by phase transitions in the oxygen condensed in closed pores. The oxygen pressure in these pores in a gas-like state is estimated to be ∼ 1000 atm. The corresponding number of O2 molecules ensures filling of the pores by condensed oxygen at low temperatures. It is established that owing to oxygen adsorption on the surface of open pores, the LFIF background is substantially enhanced in measurements performed in an oxygen environment as compared to measurements in vacuum. A hypothesis has been formulated that the oxygen pressure in closed pores and its adsorption on surfaces of open pores can be the source of critical current deterioration caused by interrupted intergrain contacts.