New phases in the binary system PbO–BiVO4: Pb2BiVO6 and Pb4BiVO8

Abstract

The binary system PbO–BiVO₄ exhibits two new phases, Pb₄BiVO₈ and Pb₂BiVO₆. They both melt congruently at 780 °C. They have been identified by single-crystal and powder X-ray diffraction. Pb₄BiVO₈ crystallizes with a triclinic cell, a= 6.221(2)Å, b= 7.603(5)Å, c= 10.457(4)Å, α= 100.40(3)°, β= 102.18(2)°, γ= 90.03(3)° and Z= 2. Pb₂BiVO₆ exhibits four phase transitions at 300, 415, 475 and 600 °C. The α phase, room-temperature form, is monoclinic with a=7.642(6)Å, b= 5.81 2(5)Å, c= 28.85(2)Å, β=100.3(1)° and Z= 8. The β and γ phases are orthorhombic with a= 8.381(6)Å, b= 16.65(1)Å, c= 4.859(6)Å, Z= 4 and a=14.304(7)Å, b=10.14(1)Å, c= 9.923(4)Å, Z= 8, respectively. The δ phase is tetragonal with a= 12.110(2)Å, c= 9.472(8)Å and Z= 8.