Principal element design of pyrochlore-fluorite dual-phase medium- and high-entropy ceramics

Site Disorder as a Predictor for Compositionally Complex 5RE2Zr2O7 Ceramic Phase Stability

“…In recent years, there has been an interest in expanding tolerance factor-based predictions to a wider range of materials systems, as well as developing new predictors for ceramic materials based on tailored compositions. 15,16,[22][23][24][25][26][27][28][29] For A 2 B 2 O 7 type materials a tolerance factor (γ), determined from the ratio of A-site and B-site ionic radii has been proposed to predict stable crystal structures. 16,20,30,31 This γ factor assumes the B-site cation is in VI-fold coordination and the A-site cation is VIII-fold coordinated.…”

“…This localized disorder has been demonstrated to be useful in determining the probability of forming a single or mixed phase material for compositionally complex A 2 B 2 O 7 zirconates and hafnates. 27,33 δ for the A-site (δ A ) is calculated as: 27,33…”

21-Component compositionally complex ceramics: Discovery of ultrahigh-entropy weberite and fergusonite phases and a pyrochlore-weberite transition

“…Although high-entropy pyrochlore oxides have been reported in several prior studies [39][40][41], the discovery of P0 (15RE 1/15 ) 2 (Ti 1/4 Zr 1/4 Ce 1/4 Hf 1/4 ) 2 O 7 is interesting not only because it is ultrahigh-entropy (~2.71k B per cation on the A sublattice and ~2.05k B per cation for the overall mean on both sublattices, Table S2 in the ESM) but also because its formation is somewhat unexpected based on the criterion for ternary oxides or conventional high-entropy pyrochlore oxides. Here, it is well established based on ternary oxides that stoichiometry A 2 B 2 O 7 should form ordered pyrochlore structure with a larger ratio of cation radii 3 A B / r r   ≈ 1.46 [71]. That study [71] proposed that a large size disorder [39]  * > ~5% may lead to a dual-phase region near the threshold for 1.4 < 14.6% for the ordered pyrochlore.…”

“…Here, it is well established based on ternary oxides that stoichiometry A 2 B 2 O 7 should form ordered pyrochlore structure with a larger ratio of cation radii 3 A B / r r   ≈ 1.46 [71]. That study [71] proposed that a large size disorder [39]  * > ~5% may lead to a dual-phase region near the threshold for 1.4 < 14.6% for the ordered pyrochlore. The size disorder would be even higher ( disorder = 19.9%) if a disordered defect-fluorite structure formed, where we used the same cation radii in the ordered pyrochlore (CN = 8 for the A-site RE elements and CN = 6 for the B-site 4+ cations based on Ref.…”

Influence of size disorder parameter on the thermophysical properties of rare‐earth‐zirconate medium‐entropy ceramics

“…Recently, medium-entropy ceramics with fewer principal elements than high-entropy ceramics had been developed and showed comparable or superior properties to their high-entropy counterparts. [20][21][22] Herein, we prepared several RE 2 Zr 2 O 7 medium-entropy ceramics based on different configuration entropies and distortion factors. The structural information, mechanical, and thermophysical properties were investigated.…”