Lithium incorporation in different high-entropy oxide systems: innovative synthesis strategies and structure-dependent impedance behavior

This work examines lithium incorporation in high-entropy oxides (HEOs) with rocksalt, fluorite, spinel, and bixbyite structures, with a focus on their potential use as next-generation electrodes, electrolytes, and multifunctional ceramics. Compositionally complex HEOs were synthesized via entropy-guided routes, and Li doping (15 mol%) was systematically evaluated using X-ray diffraction, X-ray photoelectron spectroscopy, and temperature-dependent impedance spectroscopy. XPS revealed pronounced structure-dependent changes in oxygen vacancy concentration upon Li incorporation, which translate into distinct transport responses: rock-salt HEOs show a conductivity increase of about two orders of magnitude due to mobile vacancies and Li+ in a disordered lattice, whereas fluorite and spinel phases exhibit suppressed conductivity because Li-induced defects disrupt percolating pathways. Bixbyite remains highly resistive despite a substantial increase in vacancy concentration, indicating predominantly localized or clustered defects. Porous microstructures in Li-doped spinel and rock-salt compositions further enhance charge transport, while Krivovichev's configurational entropy guides phase stability and calcination temperature.