Formation of Solid Solutions and Physicochemical Properties of the High-Entropy Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ (Ln = La, Pr, Nd, Sm or Gd) Perovskites

Abstract

Phase composition, crystal structure, and selected physicochemical properties of the high entropy Ln(Co,Cr,Fe,Mn,Ni)O3−δ (Ln = La, Pr, Gd, Nd, Sm) perovskites, as well as the possibility of Sr doping in Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ series, are reported is this work. With the use of the Pechini method, all undoped compositions are successfully synthesized. The samples exhibit distorted, orthorhombic or rhombohedral crystal structure, and a linear correlation is observed between the ionic radius of Ln and the value of the quasi-cubic perovskite lattice constant. The oxides show moderate thermal expansion, with a lack of visible contribution from the chemical expansion effect. Temperature-dependent values of the total electrical conductivity are reported, and the observed behavior appears distinctive from that of non-high entropy transition metal-based perovskites, beyond the expectations based on the rule-of-mixtures. In terms of formation of solid solutions in Sr-doped Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ materials, the results indicate a strong influence of the Ln radius, and while for La-based series the Sr solubility limit is at the level of xmax = 0.3, for the smaller Pr it is equal to just 0.1. In the case of Nd-, Sm- and Gd-based materials, even for the xSr = 0.1, the formation of secondary phases is observed on the SEM + EDS images.

Vacancy-Driven Stabilization of Sub-Stoichiometric Aluminate Spinel High Entropy Oxides

“…Previous studies report HEOs adopting a variety of different crystal structures, including rock salt, , fluorite, − spinel, − and perovskite, − which have demonstrated advantageous ionic conductivity, thermal conductivity, dielectric constants, and catalytic properties. − These oxides were stabilized solely by increasing the number of cationic elements mixed together and increasing the temperature until a phase-pure structure formed. Despite the recent development of complex perovskite and transition metal spinel HEOs, ,, many of these studies focused on stoichiometric crystal structures having a single equivalent cationic site, an approach that ultimately limits the number of parameters available to design unique complex oxides. S normalc = prefix− k normalB [ ( ∑ i = 1 N x i ln ( x i ) ) c a t i o n + ( ∑ j = 1 M y j ln ( y j ) ) a n i o n ] …”

“…14−16 These oxides were stabilized solely by increasing the number of cationic elements mixed together and increasing the temperature until a phase-pure structure formed. Despite the recent development of complex perovskite and transition metal spinel HEOs, 6,17,18 many of these studies focused on stoichiometric crystal structures having a single equivalent cationic site, an approach that ultimately limits the number of parameters available to design unique complex oxides.…”

Unusual Phase Formation in Reactively Sputter‐Deposited La—Co—O Thin‐Film Libraries

“…[21] In the context of this research, the compositional complexity of the perovskites is increasing, up to high-entropy perovskite materials. [22][23][24] Nevertheless, the pseudobinary La-Co-O oxide system is the parent system for all research based on the compositional modification of lanthanum cobaltite. Although La-Co-O is a well-explored system and the basis for many studies, [25] the influence of reactive magnetron sputtering parameters on composition, structure, and properties has not been studied systematically over large compositional ranges.…”

Layered Oxygen-Deficient Double Perovskites as Promising Cathode Materials for Solid Oxide Fuel Cells

“…The so-called compositionally complex ceramics (CCCs) include, besides HECs, medium-entropy and/or non-equimolar compositions [ 51 ]. It has been shown recently that medium- and high-entropy perovskite oxides, such as Sr(Fe α Ti β Co γ Mn ζ )O 3–δ [ 52 ], (La,Sr)(Co,Cr,Fe,Mn,Ni)O 3–δ [ 53 , 54 ], and (La,Pr,Nd,Sm,Ba,Sr)(Co,Fe,Ni,Cu)O 3–δ [ 55 ] demonstrate lower TECs with a lack of visible contribution from the chemical expansion effect and a more stable and much lower polarization resistance compared with the conventional cathode materials. These peculiarities make such materials very attractive for electrochemical applications.…”