Structural and Electrical Investigation of New Melilite Compound K_0.86Na_1.14CoP₂O₇

摘要

A new sodium-potassium cobalt diphosphate, K0.86Na1.14CoP2O7, is synthesized by solid state reactionmethod and characterized by X-ray diffraction (XRD) and impedance spectroscopy. The resultingstructural model is supports by bond-valence-sum analysis (BVS) and charge distribution validations(CHARDIT) tools. The mixed pyrophosphate crystallizes in the tetragonal system, space groupP42/mnm with a=7.808(3) ?, c=10.757(3) ?. The structure is described as a 2D anionic frameworkwith alkali cations sandwiched between layers. As mechanical grinder, ball-milling was used in orderto reduce average particle size of the prepared powder. The optimal sintering temperature of theceramic is 560°C, leading to a relative density of 83%. Their microstructure is characterized byscanning electron microscopy (SEM). The conductivity measurements of the obtained ceramic arestudied over a temperature range from 360°C to 480°C. It shows that K0.86Na1.14CoP2O7 material is alow ionic conductor with a conductivity of σ= 8.26×10-7 S.cm-1 at 390°C and an activation energy of1.34 eV. The bond valence site energy (BVSE) model is used to identify the conduction pathways forthe monovalent cations, allowing a better correlation between the electrical and the structural data.