Assessment of Novel MgCe4P6O24 Ceramic Electrolyte in Fabricating Mg-Sensors: Focus on Structure and Electrochemical Impedance Spectroscopy

Abstract

In this study, a high-temperature ceria-based phosphate ceramic electrolyte, MgCe4P6O24 prepared using a modified sol-gel chemical method produced pure dried xerogel powders is presented [1-3]. The dried xerogel powders were then calcined at 900 oC to produce MgCe4P6O24 single phase nanopowders using data extracted from thermal analysis (TGA-DSC) on the dried xerogel powders. The nanopowders were further pelletised and sintered at 1300 oC to produce a single phase dense pellets preparatory for electrochemical impedance spectroscopy analysis. X-ray diffraction (XRD) reveals that the calcined nanopowders possess an excellent crystalline structure with an average crystallite size of 52 ± 1 nm, and having a monoclinic phase, which invariably was confirmed using the High Resolution TEM (HRTEM), as presented in Figure 1. In using electrochemical impedance spectroscopy [1-3], ionic conductivity of MgCe4P6O24 ceramic electrolyte = 2.14 x 10-3 Scm-1 at an impedance bulk temperature of 744 oC was achieved. In adapting the electrochemical method [2,3], thermodynamic and kinetic data computed in this study shows the transport number of Mg2+-cation = 0.85 ± 0.03 at 700 ± 5 oC. The structural orientation, transport number and ionic conductivity data of MgCe4P6O24 ceramic electrolyte suggests the ionic conductor as a suitable solid-state ceramic electrolyte for fabricating high-temperature Mg-sensors. Figure 1(a):Bright-field TEM image showing SAED with crystalline particles (insert), and (b) HRTEM micrograph showing corresponding SAED patterns for MgCe4P6O24 nanoparticles detailing d-spacing from lattice fringes of the HRTEM patterns in b(iii).