Defect analysis of Y3+-doped Ba0.95Sr0.05Ti1-xO3-d above Curie temperature

 

Several possible defect structures in Ba0.95Sr0.05TiO3-doped with 0, 0.2, 0.4 and 0.6% molar of Y3+ have been analyzed. Polycrystalline samples used in this study were synthesized via an oxalate coprecipitation technique, subsequently followed by calcination at 700oC for 2 h and sintering at 1300oC for 2 h. Structural and microstructural characterizations using XRD and SEM show a slight decrease of lattice tetragonality (c/a) anddensification with increasing Y3+ content up to 0.4%. Electrical measurements were conducted by applying an alternating electric field of 15 V/cmwith the frequency range between 50 Hz and 1 MHz at elevated temperature from room temperature up to 300oC in air. We have noted threephenomena with respect to the characteristics of dielectric constant exhibited by the samples, namely a structural transition from tetragonal to cubicat Curie temperature, the high frequency as well as low
frequency relaxation processes occurring respectively at 180oC and 250oC. Further analysis by the Cole–Cole plot of dielectric constant and complex impedance has suggested the main cause of the elated features to be pair defects as VTi”” – VO
··  and VBa– VO·· 

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SEM images of thermally etched undoped (left) and 0.4% Y3+-doped (right) Ba0.95Sr0.05TiO3

The evolution of relative resistance during oxygen diffusion in the sample measured at the frequency 500 Hz.