Lead–strontium borate halides with hilgardite-type structure and their SHG properties

Electron density in lead bromine and chlorine hilgardites on the basis of precise x‐ray diffraction data and ab‐initio calculations and correlation with the properties

“…Our computations and the results from [20,38], demonstrate that the predominate contribution to the states close to the Fermi-level in all three compounds under investigation, is done by the oxygen atoms, that agrees with the theory of anionic groups [39]. However, the relative partial contribution of the «heavy» atoms (Pb, Sr, Br, Cl) is much higher, which explains the strong correlation between the NLO properties and the nature of the metal and halogen.…”

“…This makes clear that by the substitution of the lead atoms by Sr, as it was done by Egorova et al [20], Sr atoms are distributed among two positions uniformly, because in the other case, the dependence of the SHG intensity vs. strontium content would endure a break of the curve at the Sr/Pb ratio =1.…”

“…The HOCO pictures reveal higher PD about the oxygen atoms. Indeed, the states close to the Fermi level are build by the p-states, composed by electrons, donated by oxygen atoms [20]. The LUCO PD differs among the lead compounds and the Sr-Cl (Fig.…”

“…The framework hilgardite structure and the lead polyhedrons The structures of the orthorhombic (among with some attempts to assign tetragonal symmetry [20,28]) hilgardite modifications were solved and described for different representatives of the family (Me 2 B 5 O 9 X, Me=Ca, Sr, Ba, Pb; X=Cl, Br [9,29]). All these synthetic substances, as well as the monoclinic and triclinic modifications of natural hilgardites, have polar boron-oxygen frameworks with different symmetrical combinations of B-O-layers [30].…”

“…The peaks of the delocalized electron density were found on the residual maps in the vicinity of the Pb2 atoms and identified with the active lone pair without analysis of the topology of the density. Structural refinement using the Rietveld method on the neutron diffraction data on a powder sample and the theoretical calculations were done for the lead-chlorine hilgardite structure [20]. In the current article we present two precise X-ray diffraction experiments carried out on a spherical sample of lead-bromine hilgardite (Pb 2 [B 5 O 9 ]Br, hereinafter Pb-Br for brevity) and lead-chlorine hilgardite (Pb 2 [B 5 O 9 ]Cl, Pb-Cl) single crystals.…”