Synthesis, crystal structure and electrical proprieties of new phosphate KCoP{sub 3}O{sub 9}

• Published in: Journal of solid state chemistry 2015-01, Vol.221
• Main Authors: Ben Smida, Y., Guesmi, A., Université de Tunis El Manar, Institut Préparatoire aux Etudes d’Ingénieurs d’El Manar, El Manar II, 2092 Tunis, Georges, S., Zid, M.F.
• Format: Article
• Language: English
• Subjects: ACTIVATION ENERGY; CATIONS; COBALT OXIDES; DENSITY; ELECTRIC CONDUCTIVITY; EQUIVALENT CIRCUITS; HEXAGONAL SYSTEMS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MICROSTRUCTURE; MIGRATION; MONOCRYSTALS; PARTICLE SIZE; PHOSPHATES; POLYCRYSTALS; SCANNING ELECTRON MICROSCOPY; SIMULATION; SOLIDS; SPACE GROUPS; SYNTHESIS; THREE-DIMENSIONAL LATTICES; X-RAY DIFFRACTION
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/J.JSSC.2014.09.026

Crystals of new tricyclophosphate KCoP{sub 3}O{sub 9} have been grown from solid state reaction and characterized by single crystal X-ray diffraction. KCoP{sub 3}O{sub 9} crystallizes in the hexagonal system, space group P6{sup ¯}c2, with a=6.616 (7) Å; c=9.788 (3) Å; V=371.06 (13) Å{sup 3}, Z=2. The final agreement factors are R=0.014, ωR=0.038, S(F{sup 2})=1.231. The structure of the title compound can be described as a three-dimensional framework built up of corner sharing CoO{sub 6} and PO{sub 4} 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{sup −7} S cm{sup −1} and 1.7×10{sup −4} S cm{sup −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. - Graphical abstract: 1D pathways link K atoms along c-axis with bond valence mismatch |ΔV(K)|=0.8 v.u. - Highlights: • A new single crystal KCoP{sub 3}O{sub 9} was grown by solid state reaction and its structure determined by single-crystal X-ray diffraction. • The purity polycrystalline of KCoP{sub 3}O{sub 9} 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{sup +} cations are simulated by means of the bond valence sum model.