Influence of lone-pair cations on the germanate anomaly in glass
15 Nov 2011



Neutron diffraction has been used to prove that lone pair cations can change their behaviour as glass composition is changed.

A fragment of the network in a thallium germanate glass

Lone-pair cations in glasses are important due to the strong non-linear optical properties which they impart to the glass. Cations with a non-bonding (lone-pair) of electrons, such as lead or thallium, can adopt two different types of environment: a symmetric, highly coordinated environment, or a much more optically active, asymmetric, low coordination environment. It has long been believed that lone-pair cations change their behaviour as the glass composition is changed. However, there has been little evidence on this point until a few recent studies which have mostly not
found signs of this.

We have used neutron diffraction to study a series of thallium germanate glasses. We have shown firstly that the lone-pair thallium cations undergo a change in behaviour from a symmetric
to an asymmetric environment. Secondly, we have shown that this change is associated with the germanate anomaly – a growth and subsequent decline in the number of higher coordinated germanium VGe sites in the glass.

ER Barney, AC Hannon (ISIS), N Laorodphan, D Holland (University of Warwick)

Research date: August 2011

Further Information

Contact: Dr ER Barney,
Further reading: ER Barney et al., J. Phys. Chem. C in press (DOI: 10.1021/jp202279b)​