La6Mo8O33: a new ordered defect Scheelite superstructure

摘要

The structure of La6Mo8O33 has been determined from a triple pattern powder diffraction analysis. Two high-resolution neutron diffraction patterns collected at 1.594 and 2.398 Angstrom and one X-rays were used. This molybdate crystallizes in a non-centrosymmetric monoclinic space group P2(1) (Ndegrees4), Z = 2, a = 10.7411(3) Angstrom, b = 11.9678(3) Angstrom, c = 11.7722(3) Angstrom, beta = 116.062 (1)degrees. La6Mo8O33 is an unusual ordered defect Scheelite. Hence, it should be described with cation vacancies and an extra oxygen atom following the formula: La(6)rectangle(2)Mo(8)O(32+1). This extra oxygen atom leads to a pyramidal environment, whereas the other molybdenum atoms present tetrahedral environment. A molybdenum tetrahedral is connecting to the pyramid, forming an [Mo2O9] unit. (C) 2004 Elsevier Inc. All rights reserved.