Contrasting anion disorder behavior in Sm2Zr2O7 by simultaneous aliovalent cation substitutions and its structural and electrical properties

Abstract

In the present study, the effect of simultaneous aliovalent cation substitutions on the B site of the pyrochlore type compositions has been studied to understand the anion disorder and its influence on the electrical properties. In this regard, the Sm2Zr2 – x(YNb)x/2O7 (x = 0, 0.25, 0.5, 0.75, 1) compositions were prepared via solid-state reaction route, and the structural and electrical properties of the prepared compositions were analyzed using advanced techniques. The structural analysis studies reveal that the concentration of aliovalent cation substitution has a distinct effect on the structure; the lower concentration of Y and Nb (x ≤ 0.25) destabilizes the system, lowering the distortion, and at higher concentrations (x ≥ 0.5), it stabilizes the system. As a consequence, the distortion of BO6 increases at higher substitutions; thus, the lattice strain of the system increases, manifesting the higher anion disorder in the system. The degree of the anion disorder is further evaluated by the intensity ratio of the Raman intense Eg mode and the T2g mode around 800 cm−1 from the Raman spectrum whose trend is in line with the oxygen x-parameter variation with different concentrations of the aliovalent cation substitution. The electrical properties follow the same trend of the anion disorder and the lattice strain in the system. The maximum conductivity of 4.44 × 10−4 S/cm is obtained for the composition (x = 1) having the maximum anion disorder and lattice strain. The present study demonstrates the interrelationship among the lattice strain, anion disorder, and oxide ion conductivity, which will be helpful in designing and developing new oxide ionic conductors.