Relaxor like colossal dielectric constant in CoWO4 and CoWO4/PbWO4 nanocomposites
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Dielectric constant ε′ and dielectric loss ε″ were measured in the frequency range of 500 Hz–3 MHz from room temperature (RT) to 350 °C for CoWO4 and CoWO4/PbWO4 nanocomposites sintered at 600 °C. Dielectric constant was found to be higher for nanocomposite samples as compared to CoWO4 sample and was maximum for Pb/Co ratio optimal value of 0.028. Relaxor like anomaly and colossal dielectric constants were observed above RT due to Maxwell–Wagner effect without structural and phase transition of the materials. Relaxor like properties for these materials were confirmed by Vogel–Fulcher and modified Curie–Weiss laws. However the samples sintered at 1000 °C do not show relaxor like behaviour and exhibit low dielectric constant ε′ at RT as compared to those sintered at 600 °C. P–E curve depicts the weak ferroelectric nature of the samples.
The authors are extremely thankful to Prof. R. Wordenweber, Peter Grünberg Institute (PGI) and JARA-Fundamentals of Future Information Technology, Jülich, Germany and Dr. Bholanath Pahari, Department of Physics, Goa University for their valuable discussions about Vogel – Fulcher law analysis. Mr. Girish Prabhu of Geological oceanography division, NIO, Goa for XRD measurements. One of the authors M. Jeyakanthan is grateful to UGC, New Delhi, for providing BSR fellowship.
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