Temperature dependent dielectric characterization of manganese dioxide nanostructures with different morphologies at low frequency

The beta-MnO2 microrods and alpha-MnO2 nanowires were prepared with hydrothermal methods at 160 degrees C for 48 h. The effects of the reactant concentrations on the crystal structures and morphologies of the samples were carried out. Analytical methods such as X-ray diffraction (XRD), scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) were employed to characterize the morphology and microstructure of the final products. The temperature dependent of dielectric properties of the samples from 223 K to 393 K were also characterized and discussed in detail. The results show that the crystal structures and morphologies of the samples change with the KMnO4 concentration from beta-MnO2 pyramidal microrods with diameters 2-3 mu m and lengths 3-6 mu m to alpha-MnO2 nanowires with 30-nm-diameters and 1-mu m-lengths. The dielectric constants and the dielectric loss tangents decrease with the frequency but increase with the temperature. The samples prepared at moderate KMnO4 concentration, which contains both nanowires and microrods in the systems, show the best dielectric permittivity and loss tangents. (C) 2010 Elsevier B.V. All rights reserved.