X-RAY-POWDER DIFFRACTION STUDIES OF THE BISR3-XLAXO5.5-Y SECTION (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1) OF THE BI-SR-LA-O SYSTEM

The BiSr3-xLaO5.5-y section (0 less-than-or-equal-to x less-than-or-equal-to 1) of the Bi-Sr-La-O system was investigated by X-ray powder diffraction based on a series of samples quenched from 850-degrees-C in air. Analysis of powder diagrams and lattice parameters led to the identification of four separate regions of phase equilibria along the line connecting the BiSr3O5.5-y (beta form) and BiSr2LaO6 terminals: (i) 0 < x less-than-or-equal-to 0.2, a two-phase interval of coexistence of the beta form and a lanthanum-doped alpha form of the BiSr3O5.5-y phase; (ii) 0.2 < x less-than-or-equal-to 0.5, a single-phase domain of the Bi(5-x)+Sr3-xLaxO5.5-type solid solution of the alpha form structural type; (iii) 0.5<x<0.875, an interval of coexistence of the alpha form and a gamma phase; (iv) 0.875 less-than-or-equal-to x less-than-or-equal-to 1, a multiphase region with the gamma phase as a major component. The stabilization effect of La2O3 on the low temperature alpha-BiSr3O5.5 phase is discussed