Crystal growth of a series of lithium garnets Ln3Li5Ta2O12 (Ln=La, Pr, Nd): Structural properties, Alexandrite effect and unusual ionic conductivity

We report the single crystal structures of a series of lanthanide containing tantalates, Ln3Li5Ta2O12 (Ln=La, Pr, Nd) that were obtained out of a reactive lithium hydroxide flux. The structures of Ln3Li5Ta2O12 were determined by single crystal X-ray diffraction, where the Li+ positions and Li+ site occupancies were fixed based on previously reported neutron diffraction data for isostructural compounds. All three oxides crystallize in the cubic space group Ia3¯d (No. 230) with lattice parameters a=12.7735(1), 12.6527(1), and 12.5967(1) Å for La3Li5Ta2O12, Pr3Li5Ta2O12, and Nd3Li5Ta2O12, respectively. A UV–Vis diffuse reflectance spectrum of Nd3Li5Ta2O12 was collected to explain its unusual Alexandrite-like optical behavior. To evaluate the transport properties of Nd3Li5Ta2O12, the impedance data were collected in air in the temperature range 300⩽T(°C)⩽500.

Crystal structure of garnets Ln3Li5Ta2O12 (Ln=La, Pr, Nd). TaO6 polyhedra are shown in yellow and Ln3+ are shown as light blue spheres. Octahedrally and tetrahedrally coordinated Li+ ions are shown in green and brown, respectively. Oxygen atoms are omitted for clarity.Figure optionsDownload as PowerPoint slide