Characterisation of Pb(Mn1/3Nb2/3)O3 ceramics by SEM, XRD, XPS and dielectric permittivity tests

The Pb(Mn1/3Nb2/3)O-3 ceramics has been obtained from oxides by sintering in air, using a two-stage process with precursor columbite-like (Mn0.5Nb)O-3 phase. The PbO oxide was added in the second stage. Analysis of the X-ray diffraction pattern shows that the ceramics consist of 91% of major perovskite phase. A monoclinic distortion of the perovskite structure was found. The cell parameters are a = 12.193(3) angstrom, b = 11.966(6) angstrom, c = 12.144(2) angstrom, beta = 90 degrees 10.7'. The microanalysis made with SEM exhibited fluctuation in chemical composition of the perovskite phase. Precipitation of MnO2, PbO and the Pb-Mn-Nb-O phase different from perovskite was found. The X-ray photoelectron spectroscopy was used to study the electronic structure of the Pb(Mn1/3Nb2/3)O-3 ceramics. The core levels of lead, manganese, niobium and oxygen were measured. The shape of valence band ridge is influenced by Mn 3d states. The real average chemical composition obtained from the XPS measurement is Pb-0.99(Mn0.42Nb0.67)O-2.92. Broadband dielectric measurement was carried out in 10(-2) to 10(6) Hz and within 80-700 K ranges. The dominant relaxation process exhibits characteristic times typical for ionic processes tau(O.H) = I x 10(-11) s for the higher temperature range and, tau(O.L) = I x 10(-9) s for lower temperatures. The activation energy of relaxation process, E-M.H = 0.43 eV and E-M.L = 0.34 eV corresponds to activation energy of electric conductivity. The dielectric relaxation is ascribed to dipoles created by oxygen vacancies and/or Mn-V-O complexes. (c) 2005 Elsevier B.V. All rights reserved.