| Abstract: | To get a better understanding of the influence of rare-earth element doping,CaCu_3Ti_4O_(12)(CCTO) samples with a partial substitution of Ca with Eu with different compensation mechanisms were designed and prepared by solid-state reaction.All the ceramics were single phase,while the dielectric constants and thermally activated energy values for dielectric relaxation in Eu-doped ceramics were both lower than those of CCTO.Ca_(0.875)Eu_(0.1)Cu_3Ti_4O_(12)(CECT1)exhibited a slight decrease in both the permittivity and electric resistance of grain boundaries compared with CCTO,while Ca_(0.85)Eu_(0.1)Cu_3Ti_4O_(12)(CECT2) underwent a sharp decrease in permittivity associated with an abnormally large resistance.The different dielectric behavior indicates that the dielectric properties of CCTO are sensitive to the valence states of cations and defects.The variation of permittivity is related to the localization of carriers,which,according to the XPS results,should be caused by the presence of oxygen vacancies.The formation of defect complexes between cations and oxygen vacancies leads to the increase in resistance and prevents the hopping between Cu~+ and Cu~(2+),which is an important source of the polarization in grain boundaries. |
