Yuichi Sawai

Stability of YBa2Cu3O7, Y2Ba4Cu7O15 and YBa2Cu4O8 superconductors under varying oxygen partial pressure, total gas pressure and temperature

Abstract The phase stability of a YBCO type superconductor has been studied for different total gas pressures, oxygen partial pressures and temperatures by using a oxygen-hot-isostatic-process. A total gas pressure versus temperature phase diagram at constant oxygen partial pressure (10 Wit), and an oxygen partial pressure versus temperature phase diagram at constant total gas pressure (200 MPa) were obtained. The dependence of the phase transformation temperature of the YBCO type superconductor on the oxygen partial pressure and the total gas pressure was examined. The phase stability analysis reveals for the first time that the transformation temperature of this YBCO type superconductor depends on both the total gas pressure and the oxygen partial pressure.

A superconducting filter to separate an oxygen and argon mixture

Hot isostatic pressing in an oxygen atmosphere, known as O2-HIP method, has been used successfully to synthesize oxide materials, as well as to produce porous materials. In this paper a porous superconducting oxide is synthesized by this method and its application as a gas filter is described. Porous superconductors can be used to separate a mixture of paramagnetic and diamagnetic gases, such as oxygen and argon. Separation occurs after a magnetic field is applied and is based on the Meissner effect. Experimental results showed that the oxygen content of an oxygen/argon mixture increased after passing through a filter with large pore size (about 10 μm).

Effects of Oxygen Partial Pressure and Total Gas Pressure on Stability of YBCO type Superconductors

Phase stability of a YBCO type superconductor under variables of total gas pressure, oxygen partial pressure and temperature was studied by using oxygen hot isostatic process. A total gas pressure vs. temperature phase diagram at constant oxygen partial pressure (10MPa), and an oxygen partial pressure vs. temperature phase diagram at constant total gas pressure (200MPa) were obtained. Ago doped 124 phase was also synthesized by using 02 -HIP method. Doped Ago increased the critical temperature of the 124 phase from 75K to 77K.

Hip Phase Diagram of YBCO Type Superconductor

The oxygen partial pressure - temperature phase diagram of YBCO type superconductors reported before by us showed that the YBa 2 Cu 4 O x phase formation from Y 2 Ba 4 Cu 7 O z with CuO, as well as from YBa 2 Cu 3 O y , with CuO are oxidation reactions. The total gas pressure - temperature phase diagram shows that the YBa 2 Cu 4 O x , phase formation temperature from Y 2 Ba 4 Cu 7 O z with CuO increases with increasing the total gas pressure. On this phase boundary line, the fugacity of oxygen increases with increasing the total gas pressure even at constant oxygen partial pressure.