Structural optical and dielectric properties of single phase A[(Mg0.32Co0.02) Nb0.66]O3, where A = Ba, Sr, or Ca, compounds were studied in the temperature range from room temperature (293 K) to 458 K. The X-ray diffraction revealed that the Ba[(Mg0.32Co0.02)Nb0.66]O3 [BMCN] compounds exhibit hexagonal symmetry whereas Sr[(Mg0.32Co0.02)Nb0.66]O3 [SMCN] and Ca[(Mg0.32Co0.02)Nb0.66]O3 [CMCN] compounds exhibit monoclinic symmetry. The replacement of Barium (r = 1.61 Å) by smaller ions
like Strontium (r = 1.44 Å) or Calcium (r = 1.34 Å) in the polar dielectric Ba[(Mg0.32Co0.02) Nb0.66]O3 introduces the relaxation phenomenon and a gradual increase in the transition temperature maximum (Tm). The ac conductivity, as determined from the dielectric data, as a function of temperature and frequency,
reveals the crossover from small polaron tunneling (SPT) to correlated barrier hopping (CBH) type conduction at » 370 K. The activation energy of the non-Debye type process evaluated both from the electric modulus and the conductivity data are
nearly identical suggesting similarity in the hopping mechanism. The band gap of these materials lies in the range of narrow to wide band semi conductors.
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