Tuning the Magnetic Properties of Honeycomb Na3Co2-xNixSbO6 Systems via Electrochemistry: Evaluation of The Charge Compensation Mechanism.

The study to be conducted within the frame of the current proposal represents a part of fundamental comprehensive investigation of honeycomb Na3Co2-xNixSbO6 materials. The end members of this raw are a matter of particular interest interest for solid state physicists. Another feature of these compounds is their electrochemical activity, which might be used for tuning their structural, electronic, and consequently, magnetic properties. To be more specific, electrochemical extraction of a certain amount of sodium from a formula unit should trigger these changes. Thus, such study requires a cooperation between scientists from various research fields and a combination of synchrotron-based methods. This particular proposal is focusing on understanding the charge compensation mechanism in the named antimonates upon desodiation: both cobalt and nickel can participate in the redox process. We plan to conduct operando XAS experiments on corresponding metal K-edges with subsequent analysis of XANES and XAFS parts of the spectra. Using the reference materials, oxidation states of Co and Ni will be defined from XANES, while XAFS strucutal calculations will reveal the changes in their local coordination strucutres. These results will be put in line with those from operando XRD (a topic for a parallel proposal). Additionally, gram-scale amounts of pristine and partially desodiated antimonates are currently being prepared for neutron diffraction studies at Australian Centre for Neutron Scattering (ANSTO). These subsequent studies will focus on characterisation of crystal and magnetic structure of the named compositions at low temperatures. From the electrochemical point of view, the Na3Co2-xNixSbO6 family is a good model for studying the effects of combining various redox-active elements at the same crystallographic position on the resulting specific characteristics and kinetics of layered SIB cathodes. In the end, the outcomes should be valuable for physicists (theoreticians and experimentalists) and chemists.