High oxygen pressure (Po₂ < 3000bar) synthesis and properties of YBaCuO phases

Abstract

An overview is presented of our phase diagram, crystal growth, structural, surface and physical characterization studies of double chain compounds YBa2Cu4O8 (124) and Y2Ba4Cu7O15-x (247). The stability regions of 123, 247 and 124 phases (up to 3000 bar O2) are appreciably different for different compositions. The thermodynamics of the oxygen exchange reaction of the orthorhombic 123 with gaseous oxygen has been investigated in the pressure range 10-3-100 bar. Thermodynamics and mechanism of crystal growth have been studied by STM, AFM, SEM, X-ray and ED AX. New results of flux growth phase diagram studies are also presented. Melting of bulk 124 samples under Po2 = 1000 - 2700 bar results in ingots with Jc=4×104A/cm2 at 5K. X-ray single crystal structure analysis of 247 shows, that structural changes and incorporation of impurities occur only in the single chain "123" unit, whereas the double chain "124" unit remains stable. © 1993.