Improved glass formation and unique structure of Bi based superconducting precursor glasses with some additives

摘要

Bi based superconducting precursor glasses with the compositions M_xBi_2Sr_2Ca_2Cu_3O_y i. e. Bi-2223, (M=Al~(3+) Cr~(3+), Fe~(3+), Ga~(3+)) are prepared to improve the glass forming ability and to get information on glass structure. The main idea for these M~(3+) ion additions comes from the presence of delafossite type compounds having the formula CuMO_2 in which two oxygen coordinated Cu~+ has the role of combining octahedral MO_6 units. Additions of Al_2O_3, Cr_2O_3 and Fe_2O_3 enhance the glass formation and particularly their addition of just around x=0.8 is the most effective. The behaviour of Ga_2O_3 on glass formation in Bi-2223 is largely different from the other additives because the Ga_2O_3 addition of up to x=2.0 is effective in the glass formation. The ~(57)Fe Mossbauer spectra demonstrate that Fe ions in Bi-2223 glass are present as Fe~(3+) with tetrahedral coordination of oxygens. The network structure model in Bi based superconducting precursor glasses such as [BiO_6]-Cu-[CrO_6] or [BiO_6]Cu[FeO_4] has been proposed.