Structural, Morphological and Electrical Properties of Multi-Doped Calcium Phosphate Materials as Solid Electrolytes for Intermediate Temperature Solid Oxide Fuel Cells
Modified solution precipitation method was used to prepare pure and doped Mg, Sr and Na hydroxyapatite type materials (CaP, CaMgP and CaSrNaP). Modification consisted of partial substitution of nitrates by acetate solution in order to achieve a more soluble and cost effective synthesis. The obtained samples were calcined at 400 ºC (CaP400, CaMgP400 and CaSrNaP400). All powders were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Calcined samples were densified at 1000 ºC in an air for 3 h (CaP1000, CaMgP1000 and CaSrNaP1000). Sintered samples were characterized by XRPD, FTIR, SEM, EDS and complex impedance methods. The highest conductivity was found for the multi-doped phosphate sample (CaSrNaP1000) at 700 ºC (1.90×10-3Ω-1cm-1). The corresponding activation energies of conductivity amounted to 0.31 eV in the temperature range 500-700 ºC.
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