Abstract
Samarium (Sm3+) doped double perovskite Sr2-xSmxNiMoO6−δ (SSNM) with 0.01 ≤ x ≤ 0.05 is synthesized via citrate-nitrate auto-combustion route. X-ray analysis shows the presence of main phase with tetragonal symmetry and space group I4/m, along with a small amount of SrMoO4 phase. The amount of secondary phase is found to increase with increasing dopant concentration. Micro-structural study reveals the formation of uniform grains with grain growth inhibited by doping. XPS analysis clearly indicates the reduction of Mo6+ to Mo5+. Oxygen vacancies are also found to increase with dopant concentration. Monotonic trends of variation of conductivity and activation energy are observed. In particular, superior conductivity with lower most activation energy is obtained for the sample with x = 0.05. For this composition, impedance measurement is repeated under H2 atmosphere and a significant increase of the conductivity is observed. For air-sintered material, in addition to Mo reduction a new mechanism is proposed, based on the formation of Sr and Mo vacancies which accounts for the effect of doping on lattice parameters, phase composition and conductivity.
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