Mechanochemical synthesis and thermal stability of Ca-doped high-entropy La(Co,Cu,Fe,Mn,Ni)O3-δ perovskites

In this study, the feasibility of preparing novel Ca-doped high entropy La(Co,Cu,Fe,Mn,Ni)O 3-δ perovskites by mechanochemical synthesis was explored. It was found that monophasic compounds can be obtained after 150 h of milling, characterized by the nano size of their crystals and a significant concentration of oxygen vacancies, likely due to the incorporation of bivalent cations into the perovskite lattice. Results show that the destabilization of the perovskite structure occurs in the case of undoped compounds after thermal treatment at 1173 K, with the appearance of Ni-rich precipitates. This is inferred from in-situ XRD experiments and confirmed by TEM observations. It was found that the doped samples can be successfully described with the space group. Although certain long magnetic order can be detected in the prepared samples, the structural distortions introduced by ball milling, along with the compositional complexity, avoid the appearance of a clear ferromagnetic behavior in the samples, typical of simpler lanthanum manganites compounds. The graphical abstract illustrates the mechanochemical formation pathway of single-phase perovskites La 1-x Ca x (Co,Cu,Fe,Mn,Ni)O 3- δ (0 ≤ x ≤ 0.4). This study examines the effect of Ca 2+ substitution on the perovskite structure and the resulting cation vacancy concentration. The findings demonstrate that mechanochemistry enables the synthesis of homogeneous and stable compounds, which retain their structural integrity even after thermal treatment at temperatures up to 900 °C. • Synthesis of La 1-x Ca x (Co,Cu,Fe,Mn,Ni)O 3-δ (0 x 0.4) high entropy perovskites oxides for the first time • Detailed study of structure and thermal stability by in-situ and ex-situ measurements • First insight on the magnetic properties of the prepared HEOs