Electric permittivity and conductivity of (Na0.5Pb0.5)(Mn0.5Nb0.5)O3 ceramics

The (Na0.5Pb0.5)(Nb0.5Mn0.5)O-3 ceramics have been obtained from oxides by sintering in air, using a two-step process with precursor phase. Analysis of split lines in the XRD spectra allowed the determination of the crystallographic system of the solid solution, which consisted of one phase. The monoclinic space group P2(1)/m was identified. Cell parameters are a = 11.303(2) angstrom, b = 11.536(2) angstrom, c = 11.225(2) angstrom, beta = 88.71(2)degrees, V = 1463.4(4) angstrom(3). The high-value dielectric permittivity shows frequency dispersion in temperature characteristics. Electric modulus formalism distinguishes two relaxation processes. One is characterized with energy activation E-tau,E-A=0.36 eV and conductivity relaxation characteristic time tau(0,A) = 1 x 10(-12) s. The other with E-tau,E-B = 0.42 eV and characteristic time tau(0,B) = 2 x 10(-11) s. They were attributed to oxygen ions jumping between vacancies V-O or Mn - V-O complexes. Ionic conductivity is postulated for high temperature. Variable range hopping (vrh) small polaron conductivity manifests below 220 K. Density of states at the Fermi level, N(E-F) was estimated as 1.6 x 10(19) eV(-1) cm(-3) using the vrh model. (c) 2005 Elsevier B.V. All rights reserved.