Mechanochemical synthesis, structure and properties of lead containing alkaline earth metal fluoride solid solutions MxPb1-xF2 (M = Ca, Sr, Ba)

Abstract The paper deals with the mechanochemical synthesis of lead containing alkaline earth metal fluoride solid solutions M x Pb 1 -x F 2 (M = Ca, Sr, Ba) by high-energy ball milling. Several metal precursors and fluorinating agents were tested for synthesizing M 0.5 Pb 0.5 F 2 . Metal acetates and ammonium fluoride as precursors show the most promising results and were therefore used for the formation of M x Pb 1 -x F 2 with different metal cationic ratios. The characterization of the local fluorine coordination and the crystal structure was performed by 19 F MAS NMR spectroscopy and X-ray diffraction. Additional calculations of 19 F chemical shifts using the superposition model allow a deeper insight into the local structure of the compounds. The fluoride ion conductivity was followed by temperature dependent DC conductivity measurements. Significantly higher conductivities were found in comparison with those of the corresponding binary fluorides. The highest values were observed for samples with high lead content M 0.25 Pb 0.75 F 2 , bearing in mind the much higher conductivity of PbF 2 compared to MF 2 .