Anisotropic Alignment of Lamellar Potassium Hexaniobate Microcrystals and Nanoscrolls in a Static Magnetic Field

Microcrystals of potassium hydrogen hexaniobate (K1.8H2.2Nb6O17 ·nH2O) and nanoscrolls derived from them were suspended in an aqueous solution of tetramethyl orthosilicate and then subjected to a static homogeneous 11.74 T magnetic field as the silicate solution formed a gel. After supercritical drying of the gels, samples were studied by conventional 1D powder X-ray diffraction (XRD) in θ-θ geometry and by 2D XRD in a Debye-Scherrer geometry. Analysis of the XRD data from the field-aligned microcrystals shows that they are oriented with their crystallographic a-axis along the field direction, with an order parameter of approximately 0.9. The stacking axis of the layered solid (the b axis) is thus oriented perpendicular to the applied field. With the nanoscrolls, the 2D XRD pattern showed some evidence of some preferred orientation along the long axis of the scrolls, which could not be quantified because of the crystallographic heterogeneity of the nanoscrolls. Optical birefringence of the field-aligned nanoscroll samples was also observed. The edge-on orientation of lamellar crystals and vertical orientation of tubes and scrolls is difficult to achieve by other means and is of potential interest for membranes that exploit the in-plane transport properties of lamellar solids.