The influence of sodium deficiency and titanium doping concentration on conduction properties in NaTaO_3−δ

Abstract

NaTaO 3 shows significant proton conductivity and a high transport number of ionic conduction after being doped titanium (Ti). In this work, we aimed to determine the influence of sodium (Na) deficiency and Ti concentration in NaTaO 3 , for which NaTaO 3 samples with various Na deficiencies and Ti concentrations were prepared and characterized. The investigation was performed on microstructure, conductivity, transport number of ionic conduction, etc. Na deficiency was confirmed to decrease the conductivity of 1% Ti-doped NaTaO 3 , although it raises the conductivity of undoped NaTaO 3 . Summarizing the measured results of 1%-4% Ti-doped NaTaO 3 , a higher Ti concentration was found to significantly increase the proton conductivity of NaTaO 3 . However, when Ti is more than ∼3%, the higher concentration of Ti leads to a decrease in conductivity.Overall, ∼2% Ti was confirmed to be most beneficial to proton conductivity. The influence of phase transformation on proton conductivity was also discussed. In conclusion, precise control of Na amount is of great importance for the conduction properties of NaTaO 3 and ∼2% Ti is determined to be most beneficial to the conduction properties. In this case, through the adjustment of Ti concentration and control of Na deficiency, a bulk conductivity as high as 1.3 × 10 -3 S/cm at 600 • C and 7.8 × 10 -5 S/cm at 300 • C was realized with ∼2% Ti-doped NaTaO 3 in wet O 2 .