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An Experimental and Theoretical Insights into the Dielectric Properties of (Li, Nd) Co-doped ZnO Ceramics

In this work, we report the combined effect of donor (Nd) and acceptor (Li) co-doping at the Zn-site of ZnO ceramics on structural, microstructural and dielectric properties. Combining experimental observations with DFT based theoretical study, we have shown that before experimental fabrication DFT based first principles study can be used as a good indication to have prior qualitative assessment of a dielectric medium. For implementing this objective various Li and Nd co-doped ZnO ceramics have been synthesized through the conventional solid-state reaction route. Quantitative XRD analysis reveals the formation of wurtzite hexagonal structured ZnO having space group P63mc. Meanwhile, FESEM micrographs confirm the formation of randomly aligned non-uniform grains in size and shape. We show that the average grain size distribution and density of the studied compositions are two tuning factors to control the dielectric properties of these compounds. Though the value of dielectric constant is decreased with the increase in doping content, the optimum composition Nd0.005Li0.005Zn0.99O exhibits slightly lower dielectric constant (2066 at 1 KHz) than pristine ZnO but relatively very low dielectric loss (0.20 at 1 KHz) at room temperature than pure ZnO ceramics sintered at 1623 K. For understanding the dielectric relaxation mechanism in the studied ceramics, complex impedance spectra analysis have also been performed and discussed thoroughly. This study provides a new insight for further development of colossal permittivity (CP) ceramics and extends the current understanding of CP mechanism in ceramic materials.