Synthesis of Ni-based fluoroperovskites by solvent-free mechanochemical reaction

We realized fluoride perovskites A NiF 3 ( A = Na, K, and Ag) incorporating a transition-metal Ni element using solvent-free mechanochemical reaction processes. Methodologically, two different synthetic routes were devised based on the conventional mechanical grinding and the planetary ball milling techniques. The structural characteristics of the as-synthesized fluoroperovskite powders were determined by powder X-ray diffraction measurements and subsequent Rietveld refinement analyses. The band gaps and the chemical compositions of the A NiF 3 powders were also examined by ultraviolet–visible absorption measurements and element-specific energy dispersive X-ray spectroscopy, respectively. The goodness of factors of our refinements revealed that the high-energy planetary ball milling was more beneficial than the conventional grinding method in achieving a perovskite A NiF 3 phase mechanically. We found that the degree of mechanochemical reaction to form the perovskite phase depended on the crystal structure. With the fitted lattice parameters of the fluoride perovskites, we discussed how a structural modification induced by cation non-stoichiometry affected the stabilization of the fluoroperovskite materials via the mechanochemical synthesis.