Synthesis, crystal structure and electrical proprieties of new phosphate KCoP3O9

• A new single crystal KCoP3O9 was grown by solid state reaction and its structure determined by single-crystal X-ray diffraction.
• The purity polycrystalline of KCoP3O9 sample was verified by Rietveld refinement.
• The CIS measurements were optimized and the obtained spectra were fitted by electrical equivalent circuits.
• The conduction pathways for the K+ cations are simulated by means of the bond valence sum model.

Crystals of new tricyclophosphate KCoP3O9 have been grown from solid state reaction and characterized by single crystal X-ray diffraction. KCoP3O9 crystallizes in the hexagonal system, space group P  6¯c2, with a=6.616 (7) Å; c=9.788 (3) Å; V=371.06 (13) Å3, Z=2. The final agreement factors are R=0.014, ωR=0.038, S(F2)=1.231. The structure of the title compound can be described as a three-dimensional framework built up of corner sharing CoO6 and PO4 polyhedra containing wide tunnels oriented along [001] direction and others, less broad, along [100] and [010] directions. The structural model was validated by bond valence sum (BVS) and charge distribution (CD) methods. Ball milling was used to reduce the particles sizes of the synthesized powder. At the optimal sintering temperature of 800 °C, a relative density of 85% was obtained. The microstructure was characterized by scanning electron microscopy. The electrical conductivity was 8.4×10−7 S cm−1 and 1.7×10−4 S cm−1 at 480 °C and 680 °C respectively. The activation energy deduced from the slope is 2.2 eV at low temperature region and 1.2 eV at high temperature region. The BVS model is extended to simulate the ionic migration pathways of alkali cations in the anionic framework. The BVS calculation shows one-dimensional pathways migration along c-axis.

1D pathways link K atoms along c-axis with bond valence mismatch |ΔV(K)|=0.8 v.u. Figure optionsDownload as PowerPoint slide