A powder neutron diffraction study of stoichiometric silver beta alumina at 4.2K

The low-temperature structure of stoichiometric silver beta alumina, AgAl11O17, is described for the first time. A powder neutron diffraction study at 4.2K reveals that there is a single three-fold silver location of unit occupancy in each mirror plane. The silver site lies between the mid-oxygen and Beevers-Ross positions where the Ag-O contact distances can be minimised. The Ag-O interactions, in particular the cooperative movement of the spacer oxygens, are responsible for the superlattice which has been described previously. The Beevers-Ross, anti-Beefers-Ross and interstitial aluminium sites are vacant and the c axis is expanded relative to the non-stoichiometric parent.