Polysubstituted High-Entropy [LaNd](Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 Perovskites: Correlation of the Electrical and Magnetic Properties

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.

Visible-light photocatalytic oxygen production on a high-entropy oxide by multiple-heterojunction introduction

“…It should be noted that slight changes in the XRD profiles at 15-20º and 30-40º are due to the small amount of recovered material after photocatalysis which results in the appearance of a background effect from the sample holder, which has two humps at 15-20º and 30-40º. The stability of this catalyst particularly under visible light is not surprising because high-entropy materials usually show high stability due to their low Gibbs free energy, as shown in many other applications including Li-ion batteries [31][32][33], magnetic components [34][35][36], dielectric components [37][38][39] and thermomechanical applications [40][41][42]. In addition to the investigation of crystal structure stability by XRD, examination of the surface stability by the XPS analysis after the photocatalytic test, as shown in Fig.…”

“…Although many different methods were developed in recent years for the synthesis of HEOs [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47], a three-step synthesis was used in this study. First, small pieces of high purity Ti (99.9%), Zr (99.5%), Nb (99.9%), Ta (99.9%) and W (99.9%) in equal atomic fractions were arc-melted under an argon atmosphere in a water-cooled copper crucible to produce a metallic ingot with a total mass of ∼12 g. To improve the chemical homogeneity, the ingot was rotated and remelted 20 times in the arc melting furnace.…”

“…High-entropy ceramics are described as materials containing at least five cations, having a configurational entropy higher than 1.5R (R: gas constant) and accordingly a low Gibbs free energy and high stability [28][29][30]. Among high-entropy ceramics, HEOs are the most popular ones which are used for various applications including Li-ion batteries [31][32][33], magnetic components [34][35][36], dielectric components [37][38][39] and thermomechanical applications [40][41][42]. Moreover, there are some reports regarding the successful application of HEOs as stable catalysts for catalytic CO oxidation [43], catalytic combustion reaction [44], catalysis in electrochemical capacitors [45], electrocatalytic oxygen evolution [46], electrocatalysis in metal-air batteries [47], electrocatalytic hydrogen generation [25] and photocatalytic carbon dioxide conversion [26,48].…”

High-Entropy Oxides: Advanced Research on Electrical Properties

“…Significantly, many HEOs are based on magnetic transition metal ions; this is because electrical and magnetic properties of ferrite or manganite are strongly related to their bond lengths and bond angles, which can be easily changed by paramagnetic or diamagnetic cation substitutions [21,22]. At the same time, the disorder of the system can be further increased by controlling the concentration of doping cations and their oxidation state [23], which makes it easier for researchers to regulate HEOs' properties according to the demand. However, the fabrication temperature of HEOs is usually high, and the mechanism behind it is not yet clear, so it is necessary to conduct more studies in order to effectively guide the design and preparation of materials.…”

A-Site Cation Size Effect on Structure and Magnetic Properties of Sm(Eu,Gd)Cr0.2Mn0.2Fe0.2Co0.2Ni0.2O3 High-Entropy Solid Solutions

“…Such compounds demonstrate a unique combination of composition, structure, and physicochemical properties [21]. The most popular among high-entropy compounds are high-entropy oxides [22].…”