Undulated oxo-centered layers in PbLn$_3$O$_4$ (VO$_4$ ) (Ln= La and Nd) and relationship with Nd$_4$O$_4$(GeO$_4$ )
Résumé
Single crystals of PbLa$_3$O$_4$(VO$_4$) have been synthesized using the flux growth technique and characterized by X-ray diffraction. The crystal structure of the tittle phase was solved by charge flipping and refined to R$_1$ = 0.024 (wR$_2$ = 0.031) for 2777 reflections [I>3σ(I)]. The compound is orthorhombic and crystallized in the space group Cmcm: a = 5.8686(6)Å, b = 17.898(2)Å, c = 7.9190(7)Å, V = 831.8(1)Å3, Z = 4. The structure is built on [PbLa$_3$O$_4$]$^{3+}$ layers with zig-zag cross-sections, surrounded by isolated (VO$_4$)$_3$- tetrahedra. Its crystal structure shows direct relationship with the isoformular Nd$_4$O$_4$(GeO$_4$) compound which crystallized in the primitive non centrosymmetric Pb2$_1m$ sub-group. Its stability in temperature and under air was checked as well as optical properties. In a second part, lanthanum was substituted by neodymium giving rise to a paramagnet and f→ f electronic excitations superposed to the broad absorption front below 3.05 eV related to the presence of VO$_4$ groups.
Origine | Fichiers produits par l'(les) auteur(s) |
---|