title: Microstructures, surface properties, and topotactic transitions of manganite nanorods.
abstract: Manganite (gamma-MnOOH) nanorods with typical diameters of 20-500 nm and lengths of several micrometers were prepared by reacting KMnO(4) and ethanol under hydrothermal conditions. Synchrotron X-ray diffraction (XRD) reveal that the gamma-MnOOH nanorods crystallize in the monoclinic space group P2(1)/c with unit cell dimensions a = 5.2983(3) A, b = 5.2782(2) A, c = 5.3067(3) A, and beta = 114.401(2) degrees . Transmission electron microscopy shows that the gamma-MnOOH nanorods are single crystalline and that lateral attachment occurs for primary rods elongated along 101. X-ray photoelectron spectroscopy studies indicate that the surfaces of the gamma-MnOOH nanorods are hydrogen deficient and compensated by surface complexation. The Raman scattering spectrum features five main contributions at 360, 389, 530, 558, and 623 cm(-1) along with four weak ones at 266, 453, 492, and 734 cm(-1), attributed to Mn-O vibrations within MnO(6) octahedral frameworks. The structural stability of the gamma-MnOOH nanorods was discussed by means of in situ time-resolved synchrotron XRD. The monoclinic gamma-MnOOH nanorods transform into tetragonal beta-MnO(2) upon heating in air at about 200 degrees C. The reaction is topotactic and shows distinctive differences from those seen for bulk counterparts. A metastable, intermediate phase is observed, possibly connected with hydrogen release via the interstitial (1 x 1) tunnels of the gamma-MnOOH nanorods.
authors.affiliation: Centre for Materials Science and Nanotechnology and Department of Chemistry, University of Oslo, P.O. Box 1033, N-0315 Oslo, Norway. tao.gao@kjemi.uio.no
authors.forename: Tao
authors.initials: T
authors.lastname: Gao
authors.forename: Frank
authors.initials: F
authors.lastname: Krumeich
authors.forename: Reinhard
authors.initials: R
authors.lastname: Nesper
authors.forename: Helmer
authors.initials: H
authors.lastname: Fjellvåg
authors.forename: Poul
authors.initials: P
authors.lastname: Norby