Phase stability of bismuth lead antimony oxide

Abstract

Phase equilibria in the system (Bi 1− x Sb x ) 8Pb 5O 17 ( x=0–0.3) was studied using high temperature X-ray diffraction in combination with differential thermal analysis. Five phases were identified in this system: tetragonal Bi 8Pb 5O 17(β 2), tetragonal Bi 1.23Pb 0.77O 2.62(β 3), intermediate Φ-phase, body-centred cubic Bi 8Pb 5O 17(β), and orthorhombic Bi 3SbO 7(χ); the temperatures at which these different phases occurred were thus determined. Of particular interest in relation to undoped Bi 8Pb 5O 17, were the temperature ranges (on heating): below 420°C, pure β 2-phase; 420–460°C, coexistence of β 2-phase and Φ-phase; 460–590°C, Φ-phase; 590–615°C, a mixture of Φ-phase and β-phase; above 615°C, pure β-phase. On cooling, the high temperature β-phase transfers to the β 2-phase in the temperature range 615–590°C. Increasing the Sb concentration, x, in (Bi x Sb 1− x ) 8Pb 5O 17 caused a decrease in the temperature at which pure β-phase formed on heating. At 10 mol% Sb dopant level, the Φ-phase appears at much lower temperatures than the others. Two hypothetical binary diagrams (of Bi 8Pb 5O 17–Bi 3SbO 7) were constructed for heating and cooling regimes, respectively, which show the phases present in (Bi x Sb 1− x ) 8Pb 5O 17 over a range of different Sb concentrations ( x=0–0.3) and temperatures (room temperature to 630°C).