Titanate-based high-entropy perovskite oxides relaxor ferroelectrics

Abstract Different combinations of monovalent and trivalent A-cations in high-entropy perovskite oxides (HEPOs) were investigated. The multicomponent (A′0.2A″0.2Ba0.2Sr0.2Ca0.2)TiO3 (A′ = Na+, K+, A″ = Bi3+, La3+) perovskite compounds were successfully synthesized by solid-state reaction method persisting average cubic perovskite phase. The trivalent cation exhibited distinct effects on local structure, dielectric properties and relaxor ferroelectric behavior. Highly dense ceramics (> 95%), high dielectric constant (~ 3000), low dielectric loss (~ 0.1), and relaxor ferroelectric characteristics were obtained in the compound containing Bi3+. The La3+ containing compounds revealed lower dielectric constant, higher dielectric loss and linear dielectric behavior. The effect of monovalent cation on the dielectric properties was minimal. However, it affected relaxor ferroelectric behavior at elevated temperatures and conduction behavior at high temperatures. The (K0.2Bi0.2Ba0.2Sr0.2Ca0.2)TiO3 ceramic maintained the relaxor ferroelectric behavior with low PREM at high temperatures suggesting more stable relaxor ferroelectric characteristics than that of the (Na0.2Bi0.2Ba0.2Sr0.2Ca0.2)TiO3. Moreover, between these two compounds, the homogeneous electrical characteristics could be obtained from the compound consisting of K + and Bi + at A-site. This study suggests that tuning the chemical composition, particularly choosing appropriate combination of mono/trivalent cations in high entropy perovskite oxides, could be the effective approach to develop high-performance relaxor ferroelectrics with the desired properties

A systematic variation in cationic distribution and its influence on the magnetization of mixed-metal (nickel and zinc) cobaltite spinels

Cobaltite oxide spinel (CoCo _2 O _4 ) is one promising material that has been extensively studied for decades due to its versatile applications. Revealing the correlation among chemical compositions, cationic distributions, and physical properties are crucial for exploring its novel application. Here, a series of nickel/zinc co-substituted cobaltite spinels, Zn _1−X Ni _X Co _2 O _4 (ZNCO-X; where X = 0.00, 0.25, …, 1.00), was synthesized by calcining the hydrothermal-derived precursors and their magnetic properties have been investigated. Multiple x-ray based characterization techniques (XRD, XRF, XPS, and XAS) were applied to determine the crystalline structure and appropriated compositions of cation species (Zn ^2+ , Ni ^2+ , Ni ^3+ , Co ^2+ , and Co ^3+ ). In conjunction with Neel’s theory of antiferromagnetism, the theoretical magnetization of the spinel series was calculated based on the assumption that Zn ^2+ ion was located in tetrahedral (A site) while nickel cations (Ni ^2+ and Ni ^3+ ) occupying the octahedral (B site). The theoretical magnetization profile exhibited a good correlation. Superparamagnetic effect and cationic site exchange can be used to explain the discrepancies between the measured and calculated magnetizations. This work reported a systematic controlling of materials structure and cationic distribution, which are crucial for fine-tuning the magnetic property of the Zn _1−X Ni _X Co _2 O _4 cobaltite system