Synthesis, crystal growth, structural determination, and optical absorption spectroscopy of the magnetoplumbite type compound LaNiAl 11O 19

Abstract

Single crystals of LaNiAl 11O 19 have been grown from the melt using either the Verneuil flame fusion process or floating zone method. The resolution of the crystal structure indicates that this compound is of the distorted magnetoplumbite type (hexagonal P6 3 mmc ) and that Ni is sheared between tetrahedral and octahedral sites of the spinel blocks. This compound has also been prepared in powdered form by annealing coprecipitates of amorphous oxides at medium temperature. The thermal evolution of the coprecipitates leading to the magnetoplumbite phase has been studied simultaneously by X-ray diffraction and diffuse reflectance spectroscopy. All the main transitions of electronic spectra of the LaNiAl 11 O 19 have been assigned. The existence of a certain amount of octahedral Ni in this material makes it a possible candidate as infrared tunable laser. This potential application will be discussed in a forthcoming paper.