室温铁磁性Sr3YCo4O10.5+δ多晶有序化的烧结工艺及电磁性能

采用固相反应法制备了不同烧结温度(950~1 180 ℃)、烧结时间、烧结次数共7种工艺的Sr₃YCo₄O_10.5+δ多晶块材,通过热分析、XRD、SEM确定了有序化相变和最佳烧结工艺(1 180 ℃/24 h+1 180 ℃/24 h),并研究了多晶的电磁性能。结果表明,964 ℃完全晶化的四方相Sr₃YCo₄O_10.5在1 042 ℃吸氧(δ)完成有序化,生成Sr₃YCo₄O_10.5+δ,而1 100 ℃和1 180 ℃烧结的样品均出现(103)、(215)超结构峰,验证了其结构的有序性。块材均呈半导体电输运行为,二次烧结晶格完整性提高,晶粒长大,300 K时电阻率仅为0.06 Ω·cm,居里温度(T_c)~335 K,零场冷曲线(ZFC)上的Hopkinson峰源于低温时被冻结的磁矩随温度升高转向磁场方向,磁化强度在298 K达到最大,随后受热扰动的影响减小。室温铁磁性源于有序结构导致的中自旋或高自旋态Co³⁺的e_g轨道有序。

Sintering Process and Electrical Magnetic Properties of Ordered Room Temperature Ferromagnetism Sr3YCo4O10.5+δ Polycrystals

Sr₃YCo₄O_10.5+δ polycrystalline bulks were prepared by the solid state reaction of 7 processes with different sintering temperatures (950~1 180 ℃), sintering time and sintering times. Based on thermal analysis, XRD and SEM, order phase transition and optimal sintering process (1 180 ℃/24 h+1 180 ℃/24 h) were determined, then electrical magnetic properties of polycrystals were inverstigated. The results show that the tetragonal Sr₃YCo₄O_10.5 fully crystallized at 964 ℃ and formed the ordering Sr₃YCo₄O_10.5+δ by absorbs oxygen (δ) at 1 042 ℃. Samples sintered at 1 100 ℃ and 1 180 ℃ show superstructure peaks of (103) and (215), which verifies the order of polycrystalline structure. The bulks exhibit semiconductor behavior, secondary sintering improve the lattice integrity, grain growth and resistivity is only 0.06 Ω·cm at 300 K, Curie temperature (T_c)~335 K. Hopkinson peak on the zero field colded (ZFC) curve from the fact that the frozen magnetic moments at low temperature turn to the direction of the magnetic field as the temperature rises, the magnetization reaches the maximum at 298 K, and then decreases under the thermal disturbance. Room temperature ferromagnetism originates from the e_g orbitals ordering of the middle spin or high spin state Co³⁺ caused by the ordered structure.