Neutron Powder Diffraction, Multinuclear, and Multidimensional NMR Structural Investigation of Pb5Ga3F19

Abstract

The room temperature structure of Pb5Ga3F19 is investigated by combining neutron diffraction and multinuclear 19F, 71Ga, and 207Pb one-dimensional and two-dimensional solid-state nuclear magnetic resonance (NMR) experiments. Two models built in space group I4cm are reported for the description of the crystalline structure of Pb5Ga3F19. The structure is built from a network of both opposite corner-sharing Ga2F6(3-) octahedra forming infinite chains along the c-axis and isolated Ga1F6(3-) octahedra. The two models present two slightly different views of the strong static disorder of the fluorine ions belonging to the Ga2F6(3-) octahedra. 71Ga NMR results show that the local environment of all Ga2 ions is identical, which indicates a tilt of the Ga2F6(3-) octahedra within the chains. 207Pb NMR experiments confirm that the environment of only one of the two lead sites, Pb1, is strongly affected by the disorder, which gives rise to three broad distinct 207Pb NMR lines for this site. All 19F NMR lines are assigned using the 19F DQ-SQ MAS experiment. 19F-207Pb through-bond and through-space heteronuclear correlation experiments are carried out for the first time, supporting assignment of both the 19F and 207Pb NMR spectra. These correlation experiments also show that both models correctly describe the medium-range order of the structure of Pb5Ga3F19.