Ag1/8Pr5/8MoO4: An incommensurately modulated scheelite-type structure

作者：Morozov VA; Mironov **; Lazoryak BI; Khaikina EG; Basovich OM; Rossell MD; Van Tendeloo G^*

来源：Journal of Solid State Chemistry, 2006, 179(4): 1183-1191.

DOI：10.1016/j.jssc.2005.12.041

• complex molybdenum oxides
• X-ray diffraction
• Rietveld refinement

The crystal structure of a complex molybdenum oxide Ag1/8Pr5/8MoO4 is reported. The Ag1/8Pr5/8MoO4 sub-structure can be described on the base of the scheelite (CaWO4) structure. Transmission electron microscopy reveals that the real structure is better described in a (3+1)D formalism. According to electron diffraction study the new scheelite-type complex oxide Ag1/8P5/8MoO4 crystallizes in the B2/b(alpha beta 0)00 (3+1)D super-space group with unit cell parameters a approximate to 7.50 angstrom, b approximate to 5.30 angstrom, c approximate to 11.74 angstrom and y approximate to 135 degrees (Z = 4) and modulation vector q = 0.56a* + 0.59b*. The structure of Ag1/8Pr5/8MoO4 is refined from X-ray powder data in the scheelite setting I2/b(alpha beta 0) with a = b = 5.3013(4) angstrom, c = 11.7407(11) angstrom, q = 1.14690(14)a* + 0.58921(12)b* with fixed gamma = 90 degrees angle (R-p = 0.033, R = 0.033, Rm = 0.029 R-1 = 0.047, S = 1.36). Displacement modulations apply for all atoms. The occupancy modulation shows that one-fourth of the Ag/Pr atoms are absent. The structure call be considered as a crystallographic shear structure with incommensurate ordering of vacancies and displacement modulations for all atoms. The arrangement of Ag/Pr atonis and vacancies is at the origin of the incommensurate modulation ill the cation-deficient Ag1/8Pr5/8MoO4 phase.

• 出版日期2006-4