The magnetic and magnetocaloric effects of potassium-substituted La_0.8-xK_xBa_0.05Sr_0.15MnO₃ (0 ≤ x ≤ 0.20) manganite were explored. The samples in polycrystalline form were synthesized by the sol–gel method, with a final sintering temperature of 1100 °C. Powder X-ray diffraction (XRD) patterns refined by Rietveld refinement show that all samples crystallized in rhombohedral structure with R-3c space group. The unit cell volume of the samples decreases with increasing potassium concentration. In addition, small changes in average bond length and bond angle are also observed in the samples. Scanning electron microscope (SEM) images reveal that the largest average grain size was observed for x = 0.10. Field-cooled (FC) magnetization measurements show that the Curie temperature () of the samples increases from 320 K for x = 0 to 360 K for x = 0.2. The largest magnetocaloric (MCE) effect, which is represented by maximum magnetic entropy change (−), reaches its greatest value for the x = 0.10 sample. The monotonous increase in suggests that T_C is mainly governed by the ferromagnetic coupling between Mn ions induced by the changes on average bond length and bond angle. The obtained − value suggests that MCE property is more sensitive to Zener theory of double exchange, which is strongly related to the Mn³⁺/Mn⁴⁺ ratio of the samples.

中文翻译：

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钾替代在La0.8−xKxBa0.05Sr0.15MnO3（0≤x≤0.20）的磁性能和磁热效应中的作用

钾取代的La _{0.8- x} K _x Ba _0.05 Sr _0.15 MnO ₃（0≤x≤0.20）的锰矿。多晶形式的样品通过溶胶-凝胶法合成，最终烧结温度为1100°C。通过Rietveld精炼得到的粉末X射线衍射（XRD）图谱显示，所有样品均以具有R-3c空间基团的菱面体结构结晶。样品的晶胞体积随着钾浓度的增加而降低。另外，在样品中还观察到平均键长和键角的微小变化。扫描电子显微镜（SEM）图像显示，对于x = 0.10 ，观察到最大的平均晶粒尺寸。场冷却（FC）磁化强度的测量显示的从320 K为样品增加居里温度（℃）X = 0至360 K中X= 0.2。对于最大的磁热（MCE）效应（以最大磁熵变（-）表示），对于x = 0.10的样本达到其最大值。单调增加表明T _C主要受平均键长和键角变化引起的Mn离子之间铁磁耦合的支配。所获得的-值表明，MCE性质对双重交换的齐纳理论更敏感，这与样品的Mn ³⁺ / Mn ⁴⁺比率密切相关。