The effect of composition, sintering parameters, frequency and temperature on the dielectric parameters of ZnO-based ceramic semiconductors (cersems) having small amounts of Bi2O3, Sb2O3, CoO, MnO2, La2O3 and/or Cr2O3 has been investigated. The unusually high dielectric constant of these composites, arising due to a two-phase microstructure has been explained on the basis of a depletion layer model. The agreement in values of barrier height and donor concentration calculated fromC−2 −V plot, Hall measurement and I-V characteristics of these cersems supports the validity of barrier and depletion layer models. The depletion and inter-granular layers are estimated to be nearly 102 nm and 1–2 nm respectively. The observed variation of dielectric constant/capacitance with sintering parameters and temperature of measurement has also been explained on the basis of simplified microstructure and depletion layers. The loss peak (fmax) observed at 300 kHz remains practically unaltered with change in composition and sintering parameters. The observed dielectric dispersion in the range 102−106 Hz, exhibiting multiple relaxation times and activation energy of relaxation process as 0·36 eV, has been explained on the basis of Debye-type relaxation process originating due to trapping/detrapping and possibly due to scattering of carriers in the depletion regions.
Volume 43, 2020
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