Abstract
La-, Nd- and La/Nd-based polysubstituted high-entropy oxides (HEOs) were produced by solid-state reactions. Composition of the B-site was fixed for all samples (Cr0.2Mn0.2Fe0.2Co0.2Ni0.2) with varying of A-site cation (La, Nd and La0.5Nd0.5). Nominal chemical composition of the HEOs correlates well with initial calculated stoichiometry. All produced samples are single phase with perovskite-like structure. Average particle size is critically dependent on chemical composition. Minimal average particle size (~400 nm) was observed for the La-based sample and maximal average particle size (5.8 μm) was observed for the Nd-based sample. The values of the configurational entropy of mixing for each sample were calculated. Electrical properties were investigated in the wide range of temperatures (150–450 K) and frequencies (10−1–107 Hz). Results are discussed in terms of the variable range hopping and the small polaron hopping mechanisms. Magnetic properties were analyzed from the temperature and field dependences of the specific magnetization. The frustrated state of the spin subsystem was observed, and it can be a result of the increasing entropy state. From the Zero-Field-Cooling and Field-Cooling regimes (ZFC-FC) curves, we determine the <S> average and Smax maximum size of a ferromagnetic nanocluster in a paramagnetic matrix. The <S> average size of a ferromagnetic cluster is ~100 nm (La-CMFCNO) and ~60 nm (LN-CMFCNO). The Smax maximum size is ~210 nm (La-CMFCNO) and ~205 nm (LN-CMFCNO). For Nd-CMFCNO, spin glass state (ferromagnetic cluster lower than 30 nm) was observed due to f-d exchange at low temperatures.
Highlights
Functional materials with controlled properties based on many composite oxides are of great interest due to fundamental and practical aspects [1,2,3]
All compounds were synthesized according to the following equations: La-CMFCNO: 0.5La2 O3 + {0.1Cr2 O3 + 0.1Mn2 O3 + 0.1Fe2 O3 + 0.2CoO + 0.2NiO} + 0.1O2 (1)
%) of the resulting ceramics according to energy-dispersive X-ray spectroscopy (EDX) spectroscopy data
Summary
Functional materials with controlled properties based on many composite oxides are of great interest due to fundamental and practical aspects [1,2,3]. Mn-based complex oxides with perovskite structure (or manganites) attract great attention due to strong correlation of the chemical composition, cation ordering, crystal structure peculiarities and unique magnetic, electrical and magnetotransport properties [15,16,17,18]. Substituted manganites with general formula ABO3 (where A3+ —rare earth element such as Ln = La, Pr, Nd or substituted element; B—Mn) have a perovskite-like structure. Both A and B cations form a spatial cubic lattice in an ideal perovskite, with both partial lattices shifted relative to each other by half of the spatial diagonal of the basic cube. Chemical substitution of the A-site cations (Ln3+ ) can change the valence state of the Mn3+ [16]
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