Influence of La³⁺ Substitution on Electrical and Photocatalytic Behavior of Complex Bi₂Sn₂O₇ Oxides

Pyrochlore-type Bi 2– x La x Sn 2 O 7 (0.0 ≤ x ≤ 0.20) system has been explored for its facile synthesis and electrical and photocatalytic functionalities. The highly distorted α-polymorph of Bi 2 Sn 2 O 7 was synthesized, and successive La 3+ substitutions were found to increase the lattice symmetry. Electric field dependent polarization measurements showed the ferroelectric hysteresis loop for pure Bi 2 Sn 2 O 7 for the first time, and La 3+ substitution was found to have a bearing on the ferroelectric properties with concomitant increase in leakage current. Temperature-dependent polarization studies were also performed on various nominal compositions. Diffuse reflectance spectroscopy established the tenability of the band gap as the function of La 3+ content (2.5–3.0 eV). In order to explore the multifunctionality of this unique bismuth-containing system, the photocatalytic dye degradation of rhodamine B was investigated with Bi 2– x La x Sn 2 O 7 (0.0 ≤ x ≤ 0.20) system in both UV and visible regions. The variation in band gap introduced La 3+ substitution significantly enhanced the photocatalytic behavior of bismuth stannate for rhodamine B degradation. The rate constant for the nominal composition Bi 1.85 La 0.15 Sn 2 O 7 (17.6 × 10 –2 min –1 ) is 6-fold the value for the pure Bi 2 Sn 2 O 7 (2.75 × 10 –2 min –1 ). The degradation profiles of rhodamine B in the UV and visible regions showed that dye degradation proceeds through different mechanisms which are discussed. The present study attempts to give an insight into the variation in electrical and photocatalytic properties and relate them to changes in structure. Bi 2– x La x Sn 2 O 7 (0.0 ≤ x ≤ 0.20) system is being proposed here as multifunctional candidates for lead-free electrical materials and efficient photocatalyst in the UV and visible regions.