Emerging mixed electronic-ionic conductivity in double perovskite (La2/3Sr1/3)2(Sn1/3Fe1/3Cu1/3)2O6-δ: Phase transitions, structural, optical and dielectric study

We report on the eco-friendly synthesis of a double perovskite compound (La 2/3 Sr 1/3 ) 2 (Sn 1/3 Cu 1/3 Fe 1/3 ) 2 O 6-δ , attractive for sustainable applications due to its unique structural and conductive properties. The incorporation of Cu 2+ (3d 9 ) ions into the B sites of the perovskite structure enhanced octahedral distortion via the Jahn-Teller effect. X-ray crystallography and Rietveld structural analysis revealed a significant deviation in the octahedra of (Cu/Fe)O 6 and (Sn/Fe)O 6 from the ideal perovskite structure, resulting in a decreased overlap between the atomic orbitals. The material displays a high dielectric constant, evidenced by impedance measurements across varying temperatures and frequencies. The analysis highlighted a considerable influence of the grain intrinsic properties and the grain boundary dynamics on both the conduction mechanism and dielectric relaxation. Notably, the introduction of dopants significantly reduces the bandgap energy to 2.7 eV, compared to the 4.3 eV of SrSnO 3 . The bandgap reduction factor measured here is lower than that of other reported double-doped SrSnO 3 compounds. At 493 K, a transition in DSC measurements suggests a structural change of the conductivity from a purely electronic to an electronic-ionic conductivity. The smaller bandgap and enhanced conductivity, coupled with phase transitions lead to a mixed conductivity making this material particularly effective for the use in energy storage technologies such as supercapacitors and batteries with the aim of improving their capacity and efficiency. Additionally, due to its temperature sensitivity, it also has the potential to be used as a valuable component in sensor applications. • Incorporation of Cu 2+ enhances octahedral distortion via Jahn-Teller effect. • Introduction of dopants reduced the band gap energy from 4.3 eV to 2.7 eV. • Structural transition suggests a change from electronic to electronic-ionic conductivity.