Synthesis and structure analysis of a new sodium iron titanate Na2+xFexTi4−xO9 with x=0.65

A new member of sodium iron titanate compounds, Na2+xFexTi4−xO9 with x=0.65 has been synthesized by heating a mixture of Na2CO3, Fe2O3 and TiO2 at 1273 K in air. It crystallizes in the monoclinic system, space group C2/m with a=23.057(3) Å, b=2.945(3) Å, c=10.684(3) Å, β=103.54(2)°, and V=705.3(8) Å3. The structure was determined using single-crystal X-ray intensity data and refined to the conventional values R=4.8% and wR=4.7% for 1730 independent reflections. The basic units of the structure are built up from single, double and triple rutile-type (Ti,Fe)O6 chains along the b-axis. Three types of sodium sites are located in the large tunnel space with the site occupancy values of 1.00(1) for Na1, 0.78(1) for Na2, and 0.87(1) for Na3, respectively. The disordering and deficiency of Na2 site is well consistent with those observed in the isostructural compounds, Na2.08Ti4O9 and Na2.71Mg0.35Ti3.65O9.