Synchrotron X‐ray study of ortho­rhombic Rb3Ta5O14 with a modified pyrochlore structure

The structure of a new orthorhombic trirubidium pentatantalum oxide (Rb₃Ta₅O₁₄) phase with Pnma symmetry was identified from a half sphere of synchrotron X‐ray data measured at a wavelength of 0.85 Å. This notionally linked TaO₆ octahedral structure broadly consists of three different modifications of the pyrochlore ring motif with layer stacking normal to (205) planes. Successive pyrochlore layers do not simply stack normal to these planes but are offset along the 100] axis. An unusual aspect of this structure is the occurrence of TaO₅ trigonal bipyramids in structurally complex regions where the modified pyrochlore rings connect.