Magnetic properties of CCTO doped with GeO2

Abstract

The high dielectric constant presented by CaCu₃Ti₄O₁₂ (CCTO) makes this material promising for industrial applications, in particular for electronic devices. Nevertheless, the preparation method and the doping by oxides has a great influence on the microstructure, and consequently in the dielectric properties. In this work we prepared and studied CCTO doped by germanium oxide, in concentrations up to 10% by weight. X-ray diffraction shows the presence of nanocristals. The grains and the grain boundaries compositions have been characterized by scanning electron microscopy with energy dispersive X-ray spectrometry mapping. The magnetization measurements show an antiferromagnetic behaviour with a Néel temperature T_N=25 K, independent of the GeO₂ doping (up to 6%). Analyses of the high temperature dependence of the magnetic susceptibility show that the increase of the GeO₂ doping decreases the paramagnetic temperature. Dielectric spectroscopy measurements, in the frequency range from 75 kHz to 30 MHz, at room temperature, have been carried out. Cole-Cole model of dielectric relaxation adjusts correctly the data. The results, obtained with the different techniques, indicate that there is the increase of samples grain size up to 6% of germanium oxide, which causes an increase of the real and imaginary parts of complex permittivity.