Orientation of diamagnetic layered transition metal oxide particles in 1-tesla magnetic fields.
The magnetic field-driven orientation of microcrystals of six diamagnetic layered transition metal oxides (HLaNb(2)O(7), HCa(2)Nb(3)O(10)·0.5H(2)O, KNaCa(2)Nb(4)O(13), KTiTaO(5), KTiNbO(5), and H(2.2)K(1.8)Nb(6)O(17)·nH(2)O) suspended in epoxy resins was studied by X-ray diffraction using permanent magnets producing a 0.8 T field. Although the degree of orientation, quantified as the Hermans order parameter, was strongly affected by the particle size distribution, in all cases microcrystals with ∼1-2 μm lateral dimensions were found to orient with the magnetic field vector in the layer plane. Control of the orientation of ionically conducting layered oxides is of interest for practical applications in batteries and fuel cells. The consistent direction of orientation of the lamellar oxides studied can be rationalized in the framework of a quantitative bond anisotropy model developed by Uyeda (Phys. Chem. Miner.1993, 20, 77-80). The asymmetry of metal-oxygen bonding at the faces of the octahedral layers results in long and short M-O bonds perpendicular to the plane of the sheets. This distortion of the M-O octahedra, which is a structural feature of almost all layered materials that contain octahedral bonding frameworks, gives rise to the diamagnetic anisotropy and results in an easy axis or plane of magnetization in the plane of the sheets.
Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
Elizabeth C
EC
Sklute
Miharu
M
Eguchi
Camden N
CN
Henderson
Mark S
MS
Angelone
Hemant P
HP
Yennawar
Thomas E
TE
Mallouk
D060526:Magnetic Fields; D060328:Magnetic Phenomena; D008853:Microscopy; D010087:Oxides / Q000737:chemistry*; D028561:Transition Elements / Q000737:chemistry*; D014961:X-Ray Diffraction
D010087:Oxides; D028561:Transition Elements