Cu and Er modified barium zirconium titanate (BaZr0.05Ti0.95O3) ceramics: Composition-dependent dielectric properties

Abstract

Cu2+ and Er3+ doped BaZr0.05Ti0.95O3 (BZT) ceramics were prepared using the solid-state reaction method, where amount of CuO + Er2O3 was fixed at 2 wt.% and different CuO : Er2O3 molar ratios (i.e. 1:1, 1:2, 1:3, 2:1 and 3:1) were used. The influence of Cu2+ and Er3+ doping on crystal structure and dielectric properties of the samples sintered at 1300 ?C was investigated. X-ray diffraction analysis confirmed the formation of a single-phase material and tetragonal crystal structure with P4mm symmetry. Microstructural analysis conducted with a scanning electron microscope revealed well-defined and uniformly distributed grains across the surface of the sintered samples and reduction of grain size and density with doping. The highest energy storage density of 40.51mJ/cm3 with an energy efficiency of 78.8% was obtained in the sample with CuO : Er2O3 molar ratio of 2:1. The doped BZT ceramics have high dielectric constant and significantly lower tangent loss in comparison to the undoped BZT. The dielectric data confirm the non-Debye behaviour for all the samples. Impedance spectroscopy and electrical modulus analysis indicated that conduction in the materials was influenced by both the grains and grain boundaries. The AC conductivity is described by the Jonscher?s universal power law, whereas DC conductivity follows a dependency based on the Arrhenius?s theory. The results revealed a conduction mechanism characterized by non-overlapping small Polaron tunnelling up to 340?C and a transition to correlated barrier hopping conduction above 340?C within the selected temperature range for all the samples. According to the Arrhenius fitting of DC conductivity the activation energy of the undoped BaZr0.05Ti0.95O3 sample is 0.168 eV and decrease with doping to 0.138 and 0.131 eV for the sample with lower Cu2+ contents (CuO : Er2O3 molar ratios of 1:2 and 1:3, respectively).