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等摩尔比高熵钙钛矿陶瓷因具有优异的磁性能而备受关注. 为了进一步提升其磁化强度, 本文根据构型熵Sconfig、容差因子t和失配度σ2设计(Ln0.2La0.2Nd0.2Sm0.2Eu0.2)MnO3高熵钙钛矿陶瓷, 并通过固相法合成了单相高熵钙钛矿陶瓷, 系统研究了重稀土元素Dy, Ho和Er对所制备陶瓷的结构和磁性能的影响. 结果表明: 在1250 ℃下烧结16 h后, 所合成的高熵陶瓷试样均呈现出较高的结晶度且保持良好的结构稳定性. (Ln0.2La0.2Nd0.2Sm0.2Eu0.2)MnO3具有显著的晶格畸变效应, 其样品形貌表面光滑且晶界清晰可辨. 3种高熵陶瓷样品在T = 5 K时表现出磁滞行为, 居里温度TC随着引入稀土离子半径的减小而降低, 而饱和磁化强度和矫顽力则随之增大. 此外, 与其他样品相比, (Er0.2La0.2Nd0.2Sm0.2Eu0.2)MnO3陶瓷显示出更高的饱和磁化强度(42.8 emu/g)和矫顽力(2.09 kOe), 这归因于其磁体具有强磁晶各向异性、更大的晶格畸变σ2 (6.52×10–3)以及更小的平均晶粒尺寸(440.49 ± 22.02) nm、晶胞体积(229.432 Å3)和A位平均离子半径(1.24 Å), 其在磁记录材料方面具有应用潜力.Equimolar ratio high-entropy perovskite ceramics (HEPCs) have attracted much attention due to their excellent magnetization intensity. To further enhance their magnetization intensities, (Ln0.2La0.2Nd0.2Sm0.2Eu0.2)MnO3 (Ln = Dy, Ho and Er, labeled as Ln-LNSEMO) HEPCs are designed based on the configuration entropy Sconfig, tolerance factor t, and mismatch degree σ2. Single-phase HEPCs are synthesized by the solid-phase method in this work, in which the effects of the heavy rare-earth elements Dy, Ho and Er on the structure and magnetic properties of Ln-LNSEMO are systematically studied. The results show that all Ln-LNSEMO HEPCs exhibit high crystallinity and maintain excellent structural stability after sintering at 1250 °C for 16 h. Ln-LNSEMO HEPCs exhibit significant lattice distortion effects, with smooth surface morphology, clearly distinguishable grain boundaries, and irregular polygonal shapes. In the present work, the influences of A-site average ion radius, grain size and lattice distortion on the magnetic interactions of Ln-LNSEMO HEPCs are investigated. The three high-entropy ceramic samples exhibit hysteresis behavior at T = 5 K, with the Curie temperature TC decreasing as the radius of the introduced rare-earth ions decreases, while the saturation magnetization and coercivity increase accordingly. When the average ionic radius of A-site decreases, the interaction between their valence electrons and local electrons in the crystal increases, thereby enhancing the conversion of electrons to oriented magnetic moments under an external magnetic field. Thus, Er-LNSEMO HEPC shows a higher saturation magnetization strength (42.8 emu/g) and coercivity (2.09 kOe) than the other samples, which is attributed to the strong magnetic crystal anisotropy, larger lattice distortion σ2 (6.52×10–3), smaller average grain size (440.49 ± 22.02 nm), unit cell volume (229.432 Å3) and A-site average ion radius (1.24 Å) of its magnet. The Er-LNSEMO HEPC has potential applications in magnetic recording materials.
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Keywords:
- high-entropy ceramics /
- rare-earths /
- perovskite /
- magnetic properties
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图 1 1250 ℃下煅烧所得Ln-LNSEMO陶瓷的性质 (a) A位平均离子半径; (b)容差因子t、构型熵Sconfig和失配度σ2的理论计算值; (c) XRD图谱; (d)—(f) Rietveld精修图谱
Fig. 1. Characteristics of Ln-LNSEMO ceramics sintered at 1250 ℃: (a) Average ionic radius of A-site; (b) theoretical calculation values of tolerance factor t, configuration entropy Sconfig and mismatch degree σ2; (c) X-ray diffraction patterns; (d)–(f) rietveld refinement.
图 2 Ln-LNSEMO陶瓷Rietveld精修后的晶格参数(a)、晶胞体积(b)以及样品的晶体结构(c)
Fig. 2. Lattice parameters (a), cell volume (b) of Ln-LNSEMO ceramics after Rietveld refinement and crystal structure of samples (c)
图 3 1250 °C下烧结的Ln-LNSEMO HEPCs的SEM图、粒度分布、EDS图谱和化学成分(%) (a), (a1) Dy-LNSEMO; (b), (b1) Ho-LNSEMO; (c), (c1) Er-LNSEMO
Fig. 3. SEM micrographs, particle size distribution, EDS mapping and chemical composition (%) of Ln-LNSEMO HEPCs sintered at 1250 °C: (a), (a1) Dy-LNSEMO; (b), (b1) Ho-LNSEMO; (c), (c1) Er-LNSEMO.
图 4 Ln-LNSEMO HEPCs的高分辨率XPS光谱 (a) O 1s; (b) Mn 2p; (c) Dy 3d; (d) Ho 4d; (e) Er 4d
Fig. 4. High-resolution XPS spectra of Ln-LNSEMO HEPCs: (a) O 1s; (b) Mn 2p; (c) Dy 3d; (d) Ho 4d; (e) Er 4d.
图 5 Ln-LNSEMO HEPCs的M-T曲线(a)和dM/dT-T曲线(b)
Fig. 5. M-T curves (a) and dM/dT-T curves (b) of Ln-LNSEMO HEPCs.
图 6 Ln-LNSEMO HEPCs的T = 5 K时的磁滞回线(a)和低磁场区域(b)的磁化曲线
Fig. 6. Hysteresis loops at T = 5 K (a), the magnified magnetization curves in the low magnetic field region (b) of Ln-LNSEMO HEPCs.
表 1 氧化态、配位数(CN)和相应的离子半径(r)[23]
Table 1. Oxidation state, co-ordination number (CN) and corresponding ionic radius (r)[23].
Element Oxidation CN r/Å La 3+ XII 1.36 Nd 3+ XII 1.27 Sm 3+ XII 1.24 Eu 3+ XII 1.22 Dy 3+ XII 1.19 Ho 3+ XII 1.18 Er 3+ XII 1.11 Mn 3+ VI 0.64 O 2– VI 1.40 
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表 2 三组样品Rietveld精修后的键长d和键角θ
Table 2. Bond length d and bond angle θ of three groups of Rietveld refined samples.
Samples d Mn-O /Å θMn-O-Mn /(°) Dy-LNSEMO 1.9157(3) 148.167(6) Ho-LNSEMO 1.9357(2) 141.748(6) Er-LNSEMO 1.9500(3) 152.118(4)
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