Structure and electrical conductivity of a novel inorganic solid electrolyte: Na14.5[Al(PO4)2F2]2.5[Ti(PO4)2F2]0.5 (NATP)

A novel inorganic solid electrolyte with a layered framework structure stable up to 1043 K, Na14.5[Al(PO4)2F2]2.5[Ti(PO4)2F2]0.5 (NATP), has been hydrothermally prepared and characterized by single-crystal and powder X-ray diffraction techniques, X-ray fluorescence (XRF) analysis, IR spectroscopic measurement, thermogravimetric and differential thermal analysis (TGA and DTA). NATP crystallizes in the acentric hexagonal space group P3P3 with a=10.448(2)a=10.448(2), b=10.448(2)b=10.448(2), c=6.589(3)Å, Z=1Z=1, containing a large number of Na+ cations in the interlamellar space and the cavities of its framework. There are six different crystallographic Na+ cationic sites, in which 8% Na(5) and 12% Na(6) sites are vacant. Electrical conductivity measurements show that Na+ cations exhibit a high mobility with two domains for the electrical conductivity versus temperature.