Structural and Electrical Investigation of New Melilite Compound K0.86Na1.14CoP2O7

• Published in: International journal of electrochemical science 2018-12, Vol.13 (12), p.11648-11662
• Main Authors: Marzouki, Riadh, Smida, Youssef Ben, Guesmi, Abderrahmen, Georges, Samuel, Ali, Ismat H., Adams, Stefan, Zid, Mohamed Faouzi
• Format: Article
• Language: English
• Subjects: conduction pathways; Crystal structure; impedance spectroscopy; microstructure; relative density
• ISSN: 1452-3981; 1452-3981
• DOI: 10.20964/2018.12.75

A new sodium-potassium cobalt diphosphate, K0.86Na1.14CoP2O7, is synthesized by solid state reaction method and characterized by X-ray diffraction (XRD) and impedance spectroscopy. The resulting structural model is supports by bond-valence-sum analysis (BVS) and charge distribution validations (CHARDIT) tools. The mixed pyrophosphate crystallizes in the tetragonal system, space group P42/mnm with a=7.808(3) Å, c=10.757(3) Å. The structure is described as a 2D anionic framework with alkali cations sandwiched between layers. As mechanical grinder, ball-milling was used in order to reduce average particle size of the prepared powder. The optimal sintering temperature of the ceramic is 560°C, leading to a relative density of 83%. Their microstructure is characterized by scanning electron microscopy (SEM). The conductivity measurements of the obtained ceramic are studied over a temperature range from 360°C to 480°C. It shows that K0.86Na1.14CoP2O7 material is a low ionic conductor with a conductivity of σ= 8.26×10-7 S.cm-1 at 390°C and an activation energy of 1.34 eV. The bond valence site energy (BVSE) model is used to identify the conduction pathways for the monovalent cations, allowing a better correlation between the electrical and the structural data.