Effect of Hf doping on the structural, dielectric and optical properties of CaCu3Ti4O12 ceramic
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Ceramic samples of CaCu3(Ti1−xHfx)4O12 (CCTHO) were prepared by solid state reaction method. The influences of Hf+4 ions substitution on the structural, optical and dielectric properties of the prepared samples were investigated using X-ray diffraction, diffuse reflectance spectroscopy and impedance spectroscopy respectively. The solubility limit of Hf in CaCu3Ti4O12 (CCTO) is found to be ~2 %. The optical spectroscopy data reveals that with Hf doping the optical band gap increases. Further we observed that with Hf substitution in CCTO at Ti site improves the dielectric properties, i.e. the value of dielectric constant (ε′) increases and that of dielectric loss (tanδ) decreases with respect to parent un-doped CCTO sample. Two dielectric relaxations are observed in Hf doped sample, whereas only one relaxation is observed in CCTO. The characteristic dielectric relaxation frequency shifts towards higher values with Hf doping. Further from the fitting of ε′ versus frequency data it appears that the relaxation mechanism shifts from Debye to Cole–Cole type.
The authors would like to acknowledge Prof. Pradeep Mathur, Director, IIT Indore for his constant support and encouragement. Prof. Ravikiran Late would like to thank Dr. R. J. Barnabas, Principal, Ahmednagar College for his support. Authors also acknowledge BRNS (DAE) and CSIR India for the financial support in the form of project number 2013/37P/31/BRNS/1751 and 03(1274)/13/EMR-II respectively. Authors are thankful to Dr. A. K. Sinha, Mr. Anuj Upadhyay and Mr. Manvendra N. Singh for their help during synchrotron X-ray diffraction measurements. SIC-IIT Indore is acknowledged for XRD and SEM measurements.