Stabilization of cubic phase in Y-doped (BaSr)(Fe1-xYx)O3-δ perovskites: Sol-gel synthesis, Raman and photoluminescent characteristics

Abstract

Attempt has been made here to synthesize yttrium doped (Ba0.90Sr0.10)(Fe1-xYx)O3-δ (x = 0 – 0.20) oxides by sol-gel technique to study the influence of yttrium with regard to phase(s), strain, Raman and photoluminescent behaviour. It exhibits perovskite-type cubic and mixture of cubic and orthorhombic phases for x = 0 - 0.10 and > 0.10, respectively. The cubic lattice parameter increases linearly (a ∼4.019 - 4.054 Å, space group Pm3 m, Z = 1) with yttrium, leading to lattice expansion. Similarly, the average bond length also increases linearly (dc ∼ 2.426 - 2.447) with ‘x’. The bond angles along O-B-O and B-O-B are deviated due to the tilting and rotation of BO6 octahedra. Raman spectra reveal no band formation for the cubic phase of composition but appear for orthorhombic phase with x > 0.10. It consist bands at ∼130, 148, 222, and 372, and a broad band at ∼690 cm-1, associated with Ba/Sr bonded vibration, symmetric stretching of oxygen, and occurrence of oxygen vacancies. The photoluminescence spectra reveal peaks at ∼339, 411, 456, 486.5, and 525.5 nm (say; for x = 0.05), assigned to charge transfer transition O2p to iron and/or yttrium, interface trapping-induced radiative defects as well as shallow surface defects, and huge oxygen vacancies with trapped electrons, etc. These findings make materials useful in membrane technology.