HRTEM Studies of nm-Size FePd Particles Embedded in MgO after Annealing over 920 K
HRTEM Studies of nm-Size FePd Particles Embedded in MgO after Annealing over 920 K
复制标题
920 K 以上退火后嵌入 MgO 中的纳米级 FePd 颗粒的 HRTEM 研究
DOI：
10.2320/matertrans.44.2048
复制
发表时间：
2003
影响因子：
1.2
通讯作者：
N. Tanaka
中科院分区：
文献类型：
--
作者：
H. Pan;S. Fukami;J. Yamasaki;N. Tanaka
采用超高真空共沉积法在MgO薄膜中制备了FePd颗粒。用高分辨电子显微镜（HRTEM）研究了沉积态样品和在973 K和1073 K退火的样品。沉积态的FePd颗粒为无序的fcc相，具有1/4 0：3837 nm，并具有一定的外延取向，即[100]（001）FePdk[100]（001）MgO。颗粒尺寸约为2-3 nm，颗粒间距约为3-4 nm。沉积态样品在973 K下退火24小时后，颗粒尺寸和间距没有变化，也没有发生从无序fcc到L10有序结构的相变。唯一的变化是，在FePd颗粒的晶格条纹变得更直，定期间隔比asdeposited样品，和故障内的FePd颗粒变得比那些asdeposited样品。在1073 K下退火4 h后，样品中的颗粒尺寸约为3-4 nm，颗粒间距约为2-3 nm。粒子间发生了某种聚结。然而，没有发生从无序fcc到L10有序结构的转变。在高于体相转变温度的退火温度下不能获得L10有序结构的原因是由于FePd和MgO之间的晶格失配过大，导致小颗粒的系统能量在内部发生了应变.
FePd particles were fabricated in MgO crystalline films by using an ultra-high vacuum (UHV) co-deposition method. As-deposited samples and samples annealed at 973 K and 1073 K were studied by high resolution electron microscopy (HRTEM). The as-deposited FePd particles were in a disordered fcc phase with a ¼ 0:3837 nm and have a certain epitaxial orientations i.e. [100] (001)FePdk[100] (001)MgO. The size of particles was about 2-3 nm and separated distance of particles was about 3-4 nm. After the as-deposited sample was annealed at 973 K for 24 hours, there were neither change in particle size and separated distance, nor phase transformation to take place from disordered fcc to L10 order structure. Only change was that lattice fringes in the FePd particles became more straight and regularly spaced than those of the asdeposited sample, and faults within the FePd particles became less than those of the as-deposited sample. After the as-deposited sample was annealed at 1073 K for 4 hours, the size of particles became almost about 3-4 nm and separated distance of particles was about 2-3 nm. Some coalescence took place among the particles. There was, however, no transformation to take place from disordered fcc to L10 order structure. The reason why L10 order structure of FePd can not be obtained at such higher annealing temperature than the transformation temperature for the bulk is suggested to be that the system energy of small particle was subjected to strain inside, which is caused by large lattice mismatch between FePd and MgO.