High-entropy titanate perovskites: Nanoarchitectonics and structure-property investigations

Abstract

Phase-pure medium and high entropy (ABO₃) perovskites with multiple cations at site A and Ti at site B – (CaLaNaSr)TiO₃, (CaNaNdSr)TiO₃, (CaNaPrSr)TiO₃, (CaLaNaPbSr)TiO₃, (CaNaNdPbSr)TiO₃ and [CaNaPbSr(LaNdPr)]TiO₃ – were synthesised by a reverse co-precipitation process followed by a suitable calcination step. The calcination temperature was determined by studying the phase evolution, formation, and transformation so that a phase-pure tetragonal perovskite structure could be attained in all six systems studied. Electron microscopy revealed the particles to be highly crystalline and nano sized. The various vibrational modes and tetragonality in the lattice as well as defect states were studied using Raman spectroscopy. The band gaps of the phase-pure systems were determined using diffuse reflectance spectroscopy (DRS). The indirect band gaps of the six synthesised systems were found to be in the range of 2.51 – 3.07 eV, while the direct band gaps were in the range of 2.97 – 3.37 eV, which were less than those of the individual titanates and oxides due to the formation of defect states. The systems containing Pb showed the lowest band gap when compared to other systems. Broadband spectroscopy was used to determine the dielectric properties of the synthesised systems. The systems containing Pb showed higher dielectric constant values owing to their high tetragonality. The synthesised materials pose potential for photocatalytic applications due to their reduced band gap values.