THERMAL STABILITY, PROPERTIES AND CRYSTALLIZATION MECHANISM OF Bi-BASED PRECURSOR GLASSES

Abstract

The glass formation, thermal stability and phase separation, some phys ical properties including electrical conductivity, crystallization behaviors in Bibased precursor glasses such as Bi2Sr2CaCu20x and Bil.6Pb0.4Sr2Ca2Cu3Ox, and formation mechanism of superconducting crystals have been clarified, A key factor for an understanding for these points is the copper valence state, i.e. the ratio of Cu + and Cu 2+ , because the coordination state of Cu + and Cu 2+ in Bibased glasses might be largely different. The crystallization mechanism and kinetics are strongly affected by oxidation behaviors of Cu + to Cu 2+ .

Phase and microstructure evolution in the process of the composite Bi-2212-(Sr, Ca)3Al2O6glass-ceramics formation

“…The DTA curve (figure 2) revealed several thermal effects similar to those found for undoped BSCCO glasses [13]. The annealing temperatures for the glass were chosen taking into consideration these effects.…”

“…The phases crystallizing up to 600 • C are those observed for undoped BSCCO glasses previously [13]. However, there are different opinions about the order in which crystal phases appear and about phase assemblage at intermediate temperatures [15].…”

“…The only visible effect of the (Sr, Ca) 3 Al 2 O 6 surplus on the glass appears to be a rather large temperature interval between the glass transition and the first exothermic peak of glass crystallization (ca 75 • C). This interval for undoped BSCCO glasses is usually estimated as 50-60 • C [13].…”

“…The oxygen is consumed during this process, and therefore slow oxygen diffusion in the bulk may control the reaction. The reactions taking place between 600 and 700 • C can be proposed as follows: It is known that Bi-2212 glass melts at about 780 • C, which results in fast oxygen diffusion inside the bulk and fast formation of Bi-2212 phase [13]. Therefore on the DTA curve of the doped glass an endothermic peak at 750 • C can be assigned to the sample melting (figure 2).…”

Generation of Squeezed Vacuum Using Wavelength-Tunable Soliton Pulse and Nonlinear Polarization Interferometer

“…We connect the absence of superconductivity in Bi-2212 glass-ceramics annealed below 800 • C with low oxygen content [13,20]. However, Bi-2212 glass-ceramics usually become superconducting after annealing at 800 • C for several hours.…”