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首页> 外文期刊>RSC Advances >Role of lanthanum vacancy on the structural, magnetic and magnetocaloric properties in the lacunar perovskite manganites La0.8?x□xNa0.2MnO3 (0 ≤ x ≤ 0.15)
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Role of lanthanum vacancy on the structural, magnetic and magnetocaloric properties in the lacunar perovskite manganites La0.8?x□xNa0.2MnO3 (0 ≤ x ≤ 0.15)

机译：镧空位对腔隙钙钛矿锰矿La 0.8？ x □ x Na 0.2 MnO 3 （0≤ x ≤0.15）

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摘要

Lacunar La0.8?x□xNa0.2MnO3 (0 ≤ x ≤ 0.15) ceramics where □ is a lanthanum deficiency were synthesized via a sol–gel method. Magnetic phase transitions and magnetocaloric effects of the ceramics have been systematically studied. Structural studies using X-ray diffraction show that all compounds crystallize in the rhombohedral structure with an Rc space group. The lanthanum deficiency does not modify the crystal structure of the pristine compound (x = 0) but results in a slight change of the lattice parameters. The unit cell volume and Mn–O–Mn angle decrease with increasing deficiency content whereas the Mn–O bond length increases. This situation weakens the double-exchange interaction and hence reduces the Curie temperature (TC). By analyzing the temperature and field dependence of magnetization, we find that the La0.8?x□xNa0.2MnO3 family exhibits a second order magnetic phase transition whose critical temperature is tunable near room temperature. A considerable magnetic entropy change is observed in La0.8?x□xNa0.2MnO3 near room temperature. The maximum value of the relative cooling power (RCP) is found to be ～268 J kg?1 in La0.65□0.15Na0.2MnO3 at 5 T. This value of RCP is about ～65.3% of that obtained in gadolinium metal, known as one of the most important materials for magnetic refrigeration, at the same magnetic field change of 5 T. With increasing vacancy our manganites exhibit a stable magnetocaloric effect in a wide temperature range. The results suggest that La0.8?x□xNa0.2MnO3 and its composite materials could be expected to have effective applications for magnetic refrigeration near room temperature.
机译：腔隙La 0.8？ x □ x Na 0.2 MnO 3 （0≤ x ≤0.15）的陶瓷，其中□是镧缺乏是通过溶胶-凝胶法合成的。陶瓷的磁相变和磁热效应已得到系统地研究。使用X射线衍射进行的结构研究表明，所有化合物均在具有 R c 空间群的菱面体结构中结晶。镧缺乏不会改变原始化合物的晶体结构（ x = 0），但会导致晶格参数略有变化。晶胞体积和Mn–O–Mn角随缺陷含量的增加而减小，而Mn–O键长增加。这种情况会削弱双交换相互作用，从而降低居里温度（ T C ）。通过分析磁化强度的温度和磁场依赖性，我们发现La 0.8？ x □small <□> x Na 0.2 MnO 3 族表现出二阶磁性临界温度在室温附近可调的相变。在La 0.8？ x □ x 中观察到相当大的磁熵变化室温附近的sub> Na 0.2 MnO 3 。发现La 0.65 中的相对冷却功率（RCP）的最大值约为〜268 J kg ？1 small>□ 0.15 Na 0.2 MnO 3 在5 T时，RCP值约为金属refrigeration最重要的材料之一的金属lin中获得的RCP值的约65.3％。在磁场变化为5 T的情况下。随着空位的增加，我们的锰矿表现出稳定的性能。在宽温度范围内具有磁热效应。结果表明La 0.8？ x □ x Na 0.2 MnO 3 及其复合材料有望在房间附近的磁制冷中有效应用温度。

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