Processing and characterization of an Li7La3Zr0.5Nb0.5Ta0.5Hf0.5O12 high-entropy Li–garnet electrolyte

In this paper, we demonstrated the processing of Li₇La₃Zr_0.5Nb_0.5Ta_0.5Hf_0.5O₁₂ (LLZNTH) high-entropy Li–garnet with promising properties for lithium batteries. We first synthesized the LLZNTH Li–garnet powders which have a single cubic garnet phase (space group: $\text{◂⋅▸}Ia\overline{3}d$; No. 230) without any secondary phases as well as uniform elements distributions. The prepared powders were further densified to a relative density of ∼94% with well-crystallized grains and good contact with the neighboring grains. Minimal grain growth can be observed in the sintering time range from 8 to 20 h, which is likely due to the sluggish effects of high-entropy compounds. The sample also maintains the cubic garnet phase along with uniform elements distribution after sintering. Electrochemical characterizations indicate that the densified sample has an adequate ionic conductivity of 4.67 × 10⁻⁴ S cm⁻¹ at room temperature, a low activation energy of 0.25 eV, and a low electronic conductivity in the order of 10⁻⁸ S cm⁻¹. The significance of designing high-entropy electrolyte is further discussed.     

Phase pure rhombohedral R3¯m$R\bar{3}m$ AgCoO2 delafossite: Rietveld,selected area electron diffraction,X-ray photoemission spectroscopy,and magnetic studies

A p-type rhombohedral AgCoO₂ (S.G. $R\overline{3}m$) reported to form only at pressures greater than 300 MPa at 773 K, is stabilized in pure phase at 0.2 MPa oxygen pressure. Analysis of powder X-ray diffraction pattern by Rietveld and selected area electron diffraction patterns confirms the purity of rhombohedral phase. Core-shell X-ray photoemission spectroscopy studies show that Ag ions are in +1 oxidation state with Co ions largely in +3 state. AgCoO₂ is paramagnetic undergoing super-paramagnetic transition at 44 K. The magnetic moment of Co is 0.001 μB which corresponds to low spin (LS) Co³⁺ along with a small fraction of LS Co⁴⁺ ions.