Hole-doped high entropy ferrites: Structure and charge compensation mechanisms in (Gd0.2La0.2Nd0.2Sm0.2Y0.2)1−xCaxFeO3

Abstract

High entropy oxides (HEOs) can be defined as single-phase oxide solid solutions with five or more cations in near equiatomic proportion occupying a given cation sub-lattice. The compositional flexibility while retaining the phase purity can be considered one of the major strengths of this materials class. Taking advantage of this aspect, here we explore the extent to which an aliovalent hole dopant can be incorporated into a perovskite-HEO system. Nine systems, (Gd0.2La0.2Nd0.2Sm0.2Y0.2)1−xCaxFeO3, with varying amount of Ca content (x = 0–.5) are synthesized using nebulized spray pyrolysis. Single-phase orthorhombic (Pbnm) structure can be retained up to 20% of Ca doping. Beyond 20% of Ca, a secondary rhombohedral (R-3c) phase emerges. The 57Fe Mössbauer spectra indicate that charge compensation occurs only via oxygen vacancy formation in the single-phase systems containing up to 15% of Ca. In addition, partial transition from Fe3+ to Fe4+ occurs in the 20% Ca-doped case. Room temperature Mössbauer spectroscopy further reflects the coexistence of multiple magnetic phases in crystallographic single-phase (Gd0.2La0.2Nd0.2Sm0.2Y0.2)1−xCaxFeO3, which is supported by magnetometry measurements. These initial results show the potential of charge doping to tune structural–magneto–electronic properties in compositionally complex HEOs, warranting further research in this direction.