Acta Crystallographica Section B

Structural Science

Volume 52, Part 2 (April 1996)

research papers

Acta Cryst. (1996). B52, 260-265 [ doi:10.1107/S0108768195013310 ]

Structure and optical non-linearity of PbO.2B₂O₃

D. L. Corker and A. M. Glazer

Abstract: The crystal structure of lead tetraborate, PbO.2B₂O₃, has been refined using single-crystal X-ray diffraction data (Mo K [alpha] radiation, [lambda] = 0.71069 Å). Crystal data at room temperature: M_r = 362.43, orthorhombic, P2₁nm (C⁷_2v), a = 4.251 (2), b = 4.463 (3), c = 10.860 (3) Å, V = 206.04 Å³ with Z = 2, = 402.6 cm^-1, D_x = 5.88 Mg m^-3, F(000) = 316, final R = 0.022, wR = 0.025 over 655 reflections with I > 2.5(I). Atomic coordinates are in general agreement with those previously reported for the isostructural compound, SrO.2B₂O₃, by Perloff & Block [Acta Cryst. (1966), 20, 274-279]. All the borons are tetrahedrally coordinated with a three-dimensional network formed from O atoms that are common to either two or three tetrahedra. The tetrahedra show deformation because the B-O bonds involving the two-coordinated O atoms are much shorter than those involved with three-coordinated O atoms. The Pb atoms are situated in empty tunnels running along [010] left by the network of tetrahedra. The Pb atoms display a highly asymmetric distribution of Pb-O bonding, with the five shortest bonds covering the range 2.483 (5)-2.664 (5) Å, being all situated to one side of the Pb atom. Preliminary investigations of the non-linear optical behaviour of lead tetraborate are also discussed. The results indicate that doping with barium should lead to a new non-linear optical material that is both phase-matchable and has a high optical non-linearity.