Novel bismuth oxosalts, β-Bi3O3(VO4) and KBi5O5(PO4)2: synthesis and effect of hydrothermal pressure on the crystal structure

Abstract

Two novel bismuth oxosalts, β-Bi₃O₃(VO₄) and KBi₅O₅(PO₄)₂, synthesized hydrothermally crystallize in the triclinic space group P with a = 5.7337 (6), b = 7.1029 (8), c = 9.298 (1) Å, α = 80.334 (3), β = 78.576 (3), γ = 68.557° (3), V = 343.58 (7) ų, Z = 8 and in the monoclinic P2₁/c space group with a = 8.0264 (6), b = 5.4616 (4), c = 27.769 (2), β = 95.697 (2), V = 1211.29 (16) ų, Z = 4, respectively. Their crystal structures are built on corrugated layers formed of the linkage of oxo-centered OBi₄ or OBi₄, OBi₅ and O(Bi,K)₄ tetrahedra sharing edges surrounded by isolated vanadate/phosphate groups. β-Bi₃O₃(VO₄) is suggested to be a high-pressure polymorph with a more symmetric crystal structure than the α-modification; this agrees with the trend of decreasing structural complexity with increasing pressure. Raman and photoluminescence spectra were measured for β-Bi₃O₃(VO₄) and KBi₅O₅(PO₄)₂. The first one exhibits a weak emission at room temperature in the red-near-infrared region with a maximum at 650–660 nm, whereas the second bismuth oxosalt emits in the green orange range with a peak at 550 nm.