  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.
