Electrical Properties of Un-doped and Doped EuTiO3-based Perovskites

Un-doped and doped EuTiO3 (ET) ceramics were prepared in 5%H2/95%N2 and N2 atmospheres at various temperatures (1350, 1450 and 1500 oC). For un-doped ET, higher pellet density (above 90%) and larger grain sized ceramics were obtained from the higher sintering temperatures, such as 1500 oC. The ceramic microstructure has an important effect on the electrical properties of the ceramics based on the sintering temperature. Pellets with a large amount of open porosity (sintered at 1350 oC) showed frequency dependent permittivity values at all temperatures and Arrhenius plots of the bulk conductivity from Impedance Spectroscopy showed a switch-over in conduction mechanism at ~ 50 – 100 K from a thermally activated process with activation energy (Ea) of ~ 10 meV (> 100 K) to one with essentially zero activation energy (< 50 K). For doped-ET ceramics, it is found that BaTiO3(BT)-ET ceramics have a wide solid solution range but there is a mixed-phase range between 5 and 15% Ba-doped ET samples. Ba-rich ceramics become too conductive to measure by Impedance Spectroscopy if they are sintered in 5%H2/95%N2 atmosphere. In general, Ba-rich ceramics show ferroelectricity and the Curie temperature, Tc, moves to lower temperature with increasing Eu-content. Eu0.5Ba0.5TiO3 shows the same sequence of polymorphic phase transitions from Rhombohedral (R) to Orthorhombic (O) to Tetragonal (T) and finally to Cubic (C) symmetry as observed for BT but at lower temperatures, in agreement with that expected on the basis of A-site cation size effects. Preliminary studies of acceptor dopants, Al and Mg on the B-site, and their influence on the electrical properties are also reported.