Effects of Mn doping on the electrical and dielectric properties of CaCu3Ti4O12 fibres

CaCu3Ti4O12 (CCTO) has attracted large interest because of its high dielectric constant (epsilon' > 10(4)), good stability over a wide temperature (100-600 K) and frequency (100 Hz <f< 10 MHz) range. Considering these properties, applications in dynamic random access memory (DRAM) and microwave devices are foreseen. In this work, the microstructure and the dielectric properties of the Mn doped and undoped CaCu3Ti4O12 fibres, grown by laser floating zone technique, with pulling rates (R-p) of 50, 20 and 5 mm/h, are reported. The doping with small amounts of Mn produced significant changes in the microstructure, dielectric and electrical properties. For the fibres doped with Mn and grown at the lowest R-p (5 mm/h) strong changes of the dielectric properties and electrical resistance are observed. Contrarily to the non-linear V/I behaviour, common to all undoped samples, a progressive change to the Ohmic behaviour is verified with the decrease of R-p and Mn doping. Moreover, the typical Maxwell-Wagner dielectric relaxation at the MHz region becomes inexistent for the fibres doped with Mn grown at lower R-p. These phenomena may be ascribed to the decrease of the potential barrier at the grain-grain boundary interfaces, as a consequence of the introduction of Mn in the CCTO lattice. The dielectric properties, measured at microwave frequencies, confirm the high dielectric constant and low values of losses. The microstructure of the fibres was analysed and correlated with the respective dielectric and electrical properties. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.