Structures in the Oxygen-Deficient Fluorite-Related RnO2n−2Homologous Series: Pr12O22

The crystal structure of Pr12O22was determined utilizing Rietveld analysis of powder neutron diffraction data (P21/c,a= 6.6850(2) Å,b= 11.6004(4) Å,c= 12.8271(4) Å, β = 99.974(1)°,V= 979.67(8) Å3; total variables 130,Rp= 3.25%, wRp= 5.02%). This structure is different from the models previously proposed, and the basic structural element is the isolated oxygen vacancy, as observed in another more-oxidized member of the RnO2n−2series, Tb11O20.