Defect structure transformation during substitution in quadruple perovskite CaCu3-xTi4-xFe2xO12 studied by positron annihilation spectroscopy

Positron annihilation spectroscopic studies have been performed to investigate the defect structural evolution in polycrystalline CaCu3-xTi4-xFe2xO12 (x = 0.0, 0.1, 0.3, 0.5 and 0.7) cubic perovskite samples. The positron lifetimes, relative intensities and Doppler-broadened annihilation lineshape parameters all indicate about the annulment of crystalline vacancies from the structure and attending porous ceramic structure at higher concentration of substitution. The compositional dependence of the intensity of the defect specific positron lifetime component clearly suggests that, in the initial stages of substitution, positron annihilates in vacancy-type defects. But, for higher concentrations of Fe3+, the materials are devoid of such defects and positron trapping takes place within the pores. The results of coincidence Doppler broadening spectroscopy measurements support such transformation in which the positron trapping sites are relocated to the ceramic pores leading to the modification of the material properties.