A novel approach to the synthesis of superionic LaF3-based multicomponent nanofluorides via trifluoroacetate precursor decomposition

Abstract

In this study, an approach for the facile and versatile synthesis of multicomponent superionic nanofluorides is proposed. The results of synthesis optimization of the tysonite-type LaF3 and La0.95Sr0.05F2.95 (sp. gr. P3‾c1) nanopowders with a particle size up to 100 nm by the trifluoroacetate precursors thermal decomposition under various conditions (dynamic vacuum and ambient atmosphere) are presented. The produced samples are characterized by X-ray diffraction, electron microscopy, and differential scanning calorimetry. Decarbonization annealing of the initial nanopowders in air at 773 K is urgent for the effective elimination of amorphous carbon formed as a result of the metal-organic precursors decomposition. The nanoceramics were pressed to a theoretical density of 75–80 % and their ion-conducting properties were measured using impedance spectroscopy. The conductivity of decarbonized La0.95Sr0.05F2.95 composition, obtained in a dynamic vacuum, is 1 × 10−3 S/cm at 500 K, which exceeds the performance of undoped LaF3 ceramics by approximately 60 times. The conductive properties of nanoceramics, produced from decarbonized vacuum-synthesized powders, are 5 times higher (1 × 10−3 Sm/cm) compared to mechanochemically fabricated ones. Air-synthesized (773 K) La0.95Sr0.05F2.95 ceramics are conducted significantly worse, although no traces of pyrohydrolysis were detected. Thus, the precursors thermal decomposition method opens up great prospects for the advanced production of ion-conducting nanomaterials based on multicomponent fluoride compounds for solid electrolyte design.