Eur. Phys. J. B (2012) 85: 236
https://doi.org/10.1140/epjb/e2012-21062-y

Regular Article

Structural investigations of the tetraborates MB₄O₇ (M  =  Pb, Sr, Ba)

¹ II. Physics Institute, University of Cologne, Zlpicher Straße 77, 50937 Kln, Germany
² Institute of Crystallography, University of Cologne, Greinstr. 6, 50939 Kln, Germany

^a Present address: Helmholtz-Zentrum Berlin fr Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany. e-mail: wolf-dieter.stein@helmholtz-berlin.de

Received: 21 December 2011
Received in final form: 10 May 2012
Published online: 5 July 2012

Abstract

The crystal structures of the tetraborates MB₄O₇ were investigated at room temperature for M  =  Sr, Pb, Ba and at 100 K for M  =  Pb, Ba. The influence of the lone electron pair of Pb²⁺ in PbB₄O₇ can be studied by comparing the isostructural compounds PbB₄O₇ and SrB₄O₇. The lone pair shows a clear displacement of the lead atom which increases upon cooling. In contrast with the Sr and Pb compounds, BaB₄O₇ crystallizes in a centrosymmetric structure. However, this structure seems to be on the border of stability, as we find strong internal stress.