Formation of Solid Solutions and Physicochemical Properties of the High-Entropy LnSr(Co,Cr,Fe,Mn,Ni)O (Ln = La, Pr, Nd, Sm or Gd) Perovskites.

Phase composition, crystal structure, and selected physicochemical properties of the high entropy Ln(Co,Cr,Fe,Mn,Ni)O (Ln = La, Pr, Gd, Nd, Sm) perovskites, as well as the possibility of Sr doping in LnSr(Co,Cr,Fe,Mn,Ni)O 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 LnSr(Co,Cr,Fe,Mn,Ni)O 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 x = 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 x = 0.1, the formation of secondary phases is observed on the SEM + EDS images.