Fig. 1: Structural and microscopic characterization of KTiPO4F.
From: Titanium-based potassium-ion battery positive electrode with extraordinarily high redox potential
a Experimental, calculated and difference XRD patterns after the Rietveld refinement. Bragg reflections are denoted as violet bars. Inset: ball-polyhedral representation of the KTiPO4F crystal structure. TiO4F2 octahedra are violet, PO4 tetrahedra—orange, oxygen atoms are shown in brown, fluorine atoms—in gray. b Selected area electron diffraction (SAED) patterns of KTiPO4F. c [100] HAADF-STEM image of KTiPO4F. Inset: enlarged part of the HAADF-STEM image with the unit cell content overlaid. Titanium atoms are depicted in red, phosphorus is green, potassium—blue. d Graphical representation of fluorine atoms (gray spheres) arrangement and Ti sites coordination. e EELS spectrum of KTiPO4F in the vicinity of Ti-L2,3 edge in comparison to the reference spectra of Ti-oxides with various oxidation states of Ti. The oxide EELS spectra perfectly corroborate with those in Ref. 69. f EPR spectrum of KTiPO4F at 86 K. Broad signal with g factor around 1.92 indicates paramagnetic Ti3+ state. g EPR spectrum of the carbon-coated KTiPO4F/C at 86 K. Broad signal with g factor around 1.92 indicates paramagnetic Ti3+ state. “#”—designated sharp signal with g = 2.003 originates from paramagnetic centers in carbon coating; inset—narrow-range EPR spectrum of the same sample showing only the sharp signal from carbon (the broad signal due to Ti3+ ions could not be seen in this narrow range). h Low-magnification HAADF-STEM image of a KTiPO4F particle agglomerate consisting of 50–150 nm particles (left, scale bar 50 nm). High-resolution TEM images of a KTiPO4F particle showing the carbon-coating (middle, right, scale bars 10 nm and 5 nm respectively).
