Phase stability and structural transitions in compositionally complex LnMO3 perovskites

High‐entropy oxides: Harnessing crystalline disorder for emergent functionality

“…13 Local disorder can result in broad magnetic phase transitions and localized spin interactions that can persist above the macroscopic phase transition temperature. 13 Rocksalt, 25 perovskite, 32,33,170 and spinel 26,81,82,145 HEO systems show magnetic tunability via cation selection, giving HEOs potential as bespoke magnetic materials. Depending on cation selection, Néel temperatures can range from ∼115 to 185 K in antiferromagnetic rare-earth-based perovskite HEOs 27 and ∼30 to 770 K in antiferromagnetic first-row transition metal spinel HEOs.…”

“…Crystallinity is defined by the combination of local point symmetry and long‐range translational symmetry. Relatively simple and high‐symmetry parent structures that participate in high‐entropy systems include rocksalt (general formula AO; space group symmetry $$Fm\bar{3}m$$), 3,25 fluorite ($${\mathrm{AO}}_{2 - {{\delta}}}$$; $$Fm\bar{3}m$$), 15,30 bixbyite (or C‐type rare‐earth oxide structure; A 2 O 3 ; $$Ia\bar{3}$$), 15,16 perovskite (ABO 3 ; $$Fm\bar{3}m$$, $$Pbnm$$, or $$R\bar{3}c$$), 31–34 spinel (AB 2 O 4 or A 3 O 4 ; typically $$Fd\bar{3}m$$ or $$F\bar{4}3m$$), 17,26,35,36 and pyrochlore (A 2 B 2 O 7 ; typically $$Fd\bar{3}m$$ or $$F\bar{4}3m$$) 37,38 . Fundamental studies on phase stability, cation site occupancy, and properties employing these simple structures continue to guide research and development of HEOs with other, more complex structures, including Ruddlesden–Popper phases, 39 silicate phases, 40–42 aluminates,…”

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 predictor is useful for anticipating the symmetry and crystal structure of perovskite type ceramics (ABX 3 ) based on the ratio of the A‐site cation to the B‐site cation ionic radii. 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 15,16,22–29 . 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 .…”

Phase Stability and Magnetic Properties of Compositionally Complex n = 2 Ruddlesden–Popper Perovskites

“…14,21,22 The magnetic properties of ABO 3 type compositionally complex perovskites have generally been antiferromagnetic in nature with a small ferrimagnetic moment as observed in both the RE(M5)O 3 and (RE5)MO 3 , where RE are rare earth elements (Gd, La, Nd, Sm, and Y) and M are transition metals (Co, Cr, Fe, Mn, and Ni). 13,14,23 A similar effect was recently reported in a study focusing on the Sm(M4)O 3 compounds where M = Co, Cr, Fe, and Mn. The difference in zero-field and field-cooled magnetization data is often attributed to glassy behavior without further investigation but is more likely due to the inhomogeneous nature of the samples.…”