Synthesis and characterisation of fluoride containing transition metal phosphate and sulfate framework materials

Abstract

A variety of transition metal and lanthanide polyhedral framework materials have been successfully synthesised and characterised. The preparation of these materials was carried out under high fluoride hydrothermal (hydrofluorothermal) conditions or with a high temperature ceramic method. The prepared material structures were characterised with single-crystal X-ray diffraction (SXRD) with further analysis by powder X-ray diffraction and scanning electron microscopy (SEM).

Fluoride containing transition metal phosphates and sulfates have several potential applications as electrode and electrolyte battery materials due to high ion transport capacities which arise from the ability of the transition metal polyhedra and phosphate/sulfate tetrahedra to connect in a multitude of combinations to form stable frameworks with sufficiently low energy pathways for lithium and sodium intercalation. The ability of the transition metal centres to undergo charge balancing redox reactions during the ionic intercalation also plays a vital role in the applications of these materials. The addition of fluoride is believed to increase the cell potential when incorporated into the polyanioic frameworks due to its high electronegativity producing an increased inductive effect.

High temperature ceramic and hydrothermal techniques employed with high fluoride reagents have produced nineteen new inorganic materials, whose structures have been characterised by SXRD. Transition metal (M = Ti, Mn, V, and Cr) and lanthanide (Ln = Y, Nd, Eu, Gd, Tb, Dy, Ho, Er) polyhedra interlinked by simple and complex anions (O2-, F-, PO43-, SO42-) formed a variety of structural motifs, from discreet complex polyhedral units, through one-dimensional chains and two dimensional layers to three-dimensional structures. Much lower dimensionality was generally observed for the fluoride sulfate phases based on titanium and manganese, while a higher dimensionality was achieved in the sodium lanthanide fluoride sulfate: NaLn(SO4)2F. These new inorganic materials add to the wealth of known structures with structural features suggestive of electrochemical/intercalation functionality.

Date of Award	24 Jun 2020
Original language	English
Awarding Institution	University of Bath
Supervisor	Muhammed Islam (Supervisor), Mark Weller (Supervisor) & Andrew Johnson (Supervisor)