High-temperature elemental segregation induced structure degradation in high-entropy fluorite oxide

Fluorite-structured oxides constitute an important category of oxides with a wide range of high-temperature applications. Following the concept of high entropy, high-entropy fluorite oxides (HEFOs) have showcased intriguing high-temperature application potential. However, unlocking this potential necessitates an assessment of their long-term stability under high-temperature conditions. In this study, we conducted a prolonged heat treatment at 1000 ℃ on typical HEFO, specifically (CeHfZrGdLa)Ox. After 100 h, high-intensity X-ray diffraction (XRD) revealed a transition from a single-phase fluorite to a multi-phase configuration. Further investigation by analytical electron microscoy (AEM) demonstrated that this degradation resulted from facilitated element diffusion and consequent escalating chemical fluctuation at high temperatures, leading to spontaneous segregation and separation of Ce and La elements, forming Ce-rich, La-poor, and La-rich phases. Notably, the La-rich phase spontaneously transformed from a fluorite structure (space group Fm3¯m) to a bixbyite structure (space group Ia3¯) at elevated temperatures, resulting in the appearance of superstructure reflection in XRD profiles and electron diffraction patterns. Despite the intricate phase decomposition, the energy band gap showed minimal variation, suggesting potential property stability of (CeHfZrGdLa)Ox across a broad range of compositions. These findings offer valuable insights into the future applications of HEFOs

A study of thermal vacancies and dislocation structure in Fe-40 at.% Al

International audienceThe densities of thermal vacancies and residual dislocations in bulk specimens of Fe-40 at.% Al have been investigated using differential dilatometry and X-ray diffraction. A large quenched-in vacancy concentration at temperatures above about 873 K was apparent from the decrease in average lattice parameter. This was correlated to a lowering of the effective enthalpy of vacancy formation from about 91 to 42 kJ mol-1, possibly caused by the presence of different types of point defect in lower- and higher- temperature regimes. The residual dislocations were found to have a major concentration on lcub100rcub planes at any given temperature. An increase in the dislocation density and a concurrent fall in the vacancy concentration was observed with a lowering of the quenching temperature from 1223 to 1073 K, indicating the possibility of vacancy annihilation at 1073 K

Ferroelectric and piezoelectric properties of Ba0.85Ca0.15Ti0.90Zr0.10O3 films in 200 nm thickness range

Lead-free piezoelectric Ba0.85Ca0.15Ti0.90Zr0.10O3 (BCZT) thin films were fabricated on Si/SiO2/TiO2/Pt (100) substrates following chemical solution deposition technique. Microstructure of the nano-sized BCZT particles crystallized in the thin film was thoroughly characterized. Ferroelectric, dielectric and piezoelectric properties of the films were investigated in detail. The BCZT films annealed at 800 degrees C temperature exhibited high remanent polarization of 25 +/- 1 C/cm(2), energy density of 17 J/cm(3), dielectric constant of 1550 +/- 50 and dielectric tunability of 50%. Converse piezoelectric coefficients (d(33)) obtained from piezo-response force microscopy (PFM) measurements on BCZT grains of different grain size (20-100 nm) distributed on the BCZT 700 film varied widely from 90 to 230 pm/V. The same for BCZT 800 measured on different grain size (30-130 nm) varied from 120 to 295 pm/V. These BCZT thin films with high dielectric, ferroelectric, and piezoelectric properties might be good alternative to the PZT films for thin film piezoelectric device applications

An advancement in the synthesis of unique soft magnetic CoCuFeNiZn high entropy alloy thin films

Discovery of advanced soft-magnetic high entropy alloy (HEA) thin films are highly pursued to obtain unidentified functional materials. The figure of merit in current nanocrystalline HEA thin films relies in integration of a simple single-step electrochemical approach with a complex HEA system containing multiple elements with dissimilar crystal structures and large variation of melting points. A new family of Cobalt–Copper–Iron–Nickel–Zinc (Co–Cu–Fe–Ni–Zn) HEA thin films are prepared through pulse electrodeposition in aqueous medium, hosts nanocrystalline features in the range of ~ 5–20 nm having FCC and BCC dual phases. The fabricated Co–Cu–Fe–Ni–Zn HEA thin films exhibited high saturation magnetization value of ~ 82 emu/g, relatively low coercivity value of 19.5 Oe and remanent magnetization of 1.17%. Irrespective of the alloying of diamagnetic Zn and Cu with ferromagnetic Fe, Co, Ni elements, the HEA thin film has resulted in relatively high saturation magnetization which can provide useful insights for its potential unexplored applications