A Novel Synthesis Pathway Towards Rare Earth Fluorides by Using Liquid and Solid State Hexafluorophosphate Salts

Abstract

This work concerns different methods to synthesize rare earth fluorides by using liquid and solid state hexafluorophosphates. Various [PF₆]⁻ sources were compared, i.e. [BMIM][PF₆], [TBA][PF₆] and KPF₆. Furthermore, the required reaction times and temperatures have been determined by XRD measurements. It turned out that [TBA][PF₆] reacts even in the solid state at moderate temperatures to yield single phase LaF₃. The use of hydroxides and oxides instead of the commonly employed nitrates as rare earth educts was successfully attempted. The reaction with rare earth hydroxide showed some peculiarities which were traced back to the specific reaction between HF and OH⁻. The reaction between [TBA][PF₆] and La(OH)₃ was studied in detail via the determination of oxygen and nitrogen concentrations as well as solid-state ¹⁹F and ¹³⁹La nuclear magnetic resonance (NMR).