Structural features of new rare earth-based mixed anions (O, S, F) compounds: relationships between optical absorption and rare earth environment

Damien Pauwels (1) , Alain Demourgues (1) , Hervé Laronze (1) , Pierre Gravereau (1) , François Guillen (1) , Olivier Isnard (2) , Alain Tressaud (1)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 Laboratoire de Cristallographie

In the structure of α-LnSF and Ln2AF4S2 (A=Ca, Sr) compounds which can be considered as formed of layer stacking, the rare earth and fluorine atoms form [Ln2F2]4+ or [Ln2AF4]4+ fluorite-type blocks which alternate with double [S2]4− layers along the c-axis. Then, it appears possible to modify the size of the fluorite-type block without any modification of its charge. In the case of rare earth oxyfluorosulfides, two new classes of compounds Ln3OF3S2 (Ln=La, Ce) and La2O1.5FS were identified. The structures of these compounds are related to α-LnSF and Ln2O2S networks. In these frameworks, the charge of the blocks containing the rare earth ions can be 2+ or 4+. These blocks alternate with single or double layers of sulfur atoms. The local geometry (number of neighbors, bond distances and angles) around the rare earth varies as a function of the number of the sulfur sheets. Absorption properties in UV-visible range are correlated with the structural features.

Mots clés: Electronic transitions; UV-visible absorption; Structure refinement; Rare earth; Fluorosulfides; Oxyfluorosulfides; Powder X-ray/neutron diffraction

Domaines: Matériaux

Damien Pauwels, Alain Demourgues, Hervé Laronze, Pierre Gravereau, François Guillen, et al.. Structural features of new rare earth-based mixed anions (O, S, F) compounds: relationships between optical absorption and rare earth environment. Solid State Sciences, 2002, 4 (11-12), pp.1471-1479. ⟨10.1016/S1293-2558(02)00038-9⟩. ⟨hal-00818787⟩