Soft chemical synthesis and crystal structure of novel hydrogen titanium oxide H2Ti12O25

We have successfully prepared H2Ti12O25 by soft chemical synthetic technique using Na2Ti3O7 as a precursor material. The crystal system is the monoclinic system, space group C2/m, and its lattice parameters were refined to be a = 12.4485(2) Å, b = 3.74414(3) Å, c = 19.9523(5) Å and β = 95.244(2)° by electron diffraction pattern and powder X-ray diffraction pattern. The crystal structure of H2Ti12O25 and lithium-ion inserted H2Ti12O25 were estimated by Monte Carlo method for the first time. As a result, the formula of the lithium-ion inserted state was Li10H2Ti12O25. From these results, theoretical capacity was estimated to be 274.6 mAh/g. The total protonic conductivities in H2Ti12O25 was estimated to be σtotal = 8.71 × 10−9 S cm−1 at room temperature from the results of AC-impedance. The estimated band gap for H2Ti12O25 is about 3.34 eV, the value of which is very similar to those for Na2Ti6O13 and Li2Ti6O13.