Abstract
A new polymorph of sodium titanate Na 2Ti 4O 9 crystallizes in the triclinic system, space group P 1 with a = 10.653(4)Å, b = 11.647(3)Å, c = 2.9392(6)Å, α = 97.25(3)°, β = 90.00(11)°, γ = 102.44(2)°, and Z = 2. The structure was determined from a single-crystal X-ray diffraction method and refined to the conventional values R = 0.053 and R w = 0.065 for 2706 independent reflections. The framework of this compound is described as a large tunnel structure, built up from single, double and triple rutile-type chains with sharing vertices, and is quite different from that of the monoclinic form, which was previously reported to have a staggered sheet structure. The present compound contains a considerable amount of Na defects. The site occupancies for three types of sodium, determined by the structure analysis, are 0.97 for Na(1), 0.48 for Na(2), and 0.63 for Na(3), and these give the chemical formula Na 2.08Ti 4O 9. The relationship to the other compounds with rutile-type tunnel structure, e.g., hollandite-type manganese oxides, is discussed.
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