Superstructure of hollandite KxMg(8+x)/3Sb(16-x)/3O16 (x approximate to 1.76)

摘要

Single crystals Of KxMg(8+x)/3Sb(16-x)/3O16 (x approximate to 1.76) with a hollandite superstructure were grown. Ordering schemes for guest ions (K) and the host structure were confirmed by the structure refinement using X-ray diffraction intensities. The space group is I4/m and cell parameters are a = 10.3256(6), c = 9.2526(17)angstrom with Z = 3. Superlattice formation is primarily attributed to the Mg/Sb occupational modulation in the host structure. Mg/Sb ratios at two nonequivalent metal sites are 0.8977/0.1023 and 0.1612/0.8388. Two types of the cavity are seen in the tunnel, where parts of K ions deviate from the cavity center along the tunnel direction. Probability densities for K ions in the two cavities are different from each other, which seems to have arisen from the Mg/Sb modulation. (c) 2007 Elsevier Inc. All rights reserved.