Ba1.09Pb0.91Be2(BO3)2F2 (BPBBF), a previously unreported
lead-containing
beryllium borate fluoride, has been successfully grown through a high-temperature
flux method. Its structure is solved by single-crystal X-ray diffraction
(SC-XRD), and it is optically characterized via infrared, Raman, UV–vis–IR
transmission, and polarizing spectra as well. SC-XRD data suggests
that it can be indexed by a trigonal unit cell (space group P
m1) with lattice
parameters a = 4.7478(6) Å, c = 8.3856(12) Å, Z = 1, and V = 163.70(5) Å. This material could be considered as a derivative
of the Sr2Be2B2O7 (SBBO)
structural motif. It consists of 2D [Be3B3O6F3]∞ layers in the crystallographic ab plane, with divalent Ba2+ or Pb2+ cations serving as spacers among the adjacent layers. Ba and Pb
were found to adopt a disordered arrangement in the trigonal prismatic
coordination within the BPBBF structural lattice, which is evidenced
by both structural refinements against SC-XRD data and energy dispersive
spectroscopy. The UV absorption edge (279.1 nm) and birefringence
(Δn = 0.054@ 546.1 nm) of BPBBF are confirmed
by UV–vis–IR transmission and polarizing spectra, respectively.
The discovery of this previous unreported SBBO-type material, BPBBF,
along with other reported analogues such as BaMBe2(BO3)2F2 (M = Ca, Mg, and Cd), provide a prodigious example for tuning the bandgap,
birefringence, and short UV absorption edge via simple chemical substitution.