Phase stabilisation in the pseudo-binary system Bi2MgO4–Bi2VO5.5−δ

Abstract The structure and electrical conductivity of compositions in the pseudo-binary system Bi 2 MgO 4 –Bi 2 VO 5.5− δ were investigated beyond the BIMEVOX stabilisation region using X-ray powder diffraction and ac impedance spectroscopy. Compositions of the general formula Bi 2 V 1− x Mg x O 5.5−3 x /2 were studied and several discrete phases were identified, viz: x =0.30, orthorhombic BIMGVOX; x =0.50, Bi 8 V 2 O 17 ; x =0.60, Bi 12 V 2 O 23 ; x =0.80, a δ-Bi 2 O 3 -type phase; and x =0.90, a γ-Bi 2 O 3 -type phase. In between these compositions, mixtures of phases are observed. High-temperature diffraction reveals phase separation at x =0.30 and 0.90. The structural data correlate well with variations in activation energy and conductivity.