Breaking Zachariasen rules - the structure of barium zirconium fluoride glasses

Glass is an essential material with applications that are dominated by oxides, but fluoride glasses (based on barium zirconium fluorides, "ZBLAN" glasses) have key applications for infrared transmission and rare earth luminescence. Although they have ionic bonding their structures do not follow the "Zachariasen rules" which predict small, well-defined network forming units. Instead ZBLAN glasses have Zr with large coordination numbers of 7 and 8. Given the limited previous structural studies of ZBLAN glasses it is important to carry out a comprehensive study using neutron and x-ray diffraction in order to better understand the structural basis for glass formation. The diffraction data will be complemented by molecular dynamics modelling, where recent work by the proposer has suggested the Zr coordination polyhedra have square antiprism geometry