J. Hernández-Velasco

Structural elucidation of the Bi(2(n + 2))Mo(n)O(6(n + 1)) (n = 3, 4, 5 and 6) family of fluorite superstructures by transmission electron microscopy.

The cationic framework structure of a whole new family of compounds with the general formula Bi(2(n + 2))Mo(n)O(6(n + 1)) (n = 3, 4, 5 and 6) has been elucidated by transmission electron microscopy (TEM) methods. High-resolution transmission electron microscopy (HRTEM) has been used to postulate heavy-atom models based on the known structure of the n = 3 phase, Bi(10)Mo(3)O(24). These models were tested by HRTEM image simulation, electron diffraction and powder X-ray diffraction simulation methods which agreed with the experimental results. The four known phases of this family correspond to n = 3, 4, 5 and 6 members and all show fluorite superstructures. They consist of a common delta-Bi(2)O(3) fluorite-type framework, inside of which are distributed ribbons of {MoO(4)} tetrahedra which are infinite along b, one tetrahedron thick along c, and of variable widths of 3, 4, 5 or 6 {MoO(4)} tetrahedra along a depending on the family member (n value). These {MoO(4)} tetrahedra are isolated, i.e. without sharing any corner as in the [Bi(12)O(14)] columnar structural-type phase Bi[Bi(12)O(14)][MoO(4)](4)[VO(4)]. The structure of all these family members can be described as crystallographic shear derivatives from Aurivillius-type phases such as Bi(2)MoO(6), the n = infinity end member. All these compounds are good oxygen-ion conductors.

Incommensurate magnetic structure and chemical modulation in SbVO4 catalyst

Oral presentation fgiven at the 24th Congress and General Assembly of the International Union of Crystallography (IUCR2017), held in Hyderabad (India) on August 21-28th, 2017.

Cationic superstructures and incommensurate magnetic structure in SbVO4 catalyst

Chemical and magnetic structure modulations in antimony vanadium mixed oxide with composition Sb0.92V1.08O4 prepared in reducing conditions are studied using diffraction techniques, mainly nuclear and magnetic neutron scattering, electron and X-ray powder diffraction. Magnetic susceptibility measurements show possible magnetic order of V3+ magnetic moments that is confirmed with neutron diffraction at TN ~50K. The average commensurate nuclear cell belongs to the tetragonal rutile structural type with cell constants: a=4.6066(11)A and c=3.0812(8)A at 60K. However the nature of the magnetic structure is incommensurate with propagation vector k= [0, 0, ± 0.266(1)] related to short range order phenomena and V-Sb alternating occupancy along the crystallographic c-axis.

Structural Characterisation by TEM of a New Homologous Series Bi2n+4MonO6(n+1); n=3,4,5 and 6

Bi2O3-MoO3 system presents many phases with a fluorite-type related structure with anion vacancies and are, therefore, good oxygen conductors. Usually, this compounds are synthesized by the traditional ceramic method. However, the high temperatures employed by this method avoid the isolation of low-temperature phases. We have used low temperature methods like the so called n-butylamine method [1].