EXAFS研究Ni-B和Ni-Ce-B超细非晶态合金的退火晶化

采用同步辐射EXAFS技术定量地研究化学还原法制备的Ni-B和Ni-Ce-B超细非晶态合金中Ni原子的局域环境结构随退火温度升高而产生的变化，结果表明，对于Ni-B和Ni-Ce-B超细非晶态合金初始样品：Ni-Ni最邻近配位壳层的平均键长RNi-Ni、配位数N、热无序σT、结构无序σs分别为0．275nm,11.9.0.0069nm,0.034nm；0.276nm,12.4,0.0067nm,0.035nm,Ni-B最邻近配位壳层的RNi-B,N, σT，σs分别为0．215nm,2.7,0.0055nm,0.0048nm；0.214nm,2.0,0.0058nm,0.0042nm,Ni-Ni配位的σs很大，是其σT的4－5倍，比Ni－B配位的σs大近一个数量级，在300℃退火后，Ni－B样品开始发生晶化生成晶态Ni3B，其RNi-Ni和σs分别为0．254nm和0．011nm,σs降低近2倍；而．3％原子比的Ce掺入后使Ni-Ce-B超细非晶态合金的晶化温度升高100℃左右。在500℃退火后，Ni－B样品的结构参数与Ni箔的相近，但Ni-Ce-B样品中的Ni-Ni配位的σs仍为0．0073nm,Ni-B配位的N为1．2，表明稀土元素Ce（以CeO2)显著增强了Ni与B的相互作用，且同时使退火晶化成的Ni晶结构产生畸变。

Annealed Crystallization of Ni-B and Ni-Ce-B Ultrafine Amorphous Alloys Studied by EXAFS

EXAFS technique was used to quantitatively determine the local structure evolutions of Ni-B and Ni-Ce-B ultrafine amorphous alloys prepared by chemical reduction during the annealed process. The results show that the average bond length Rj, coordination number N, thermal disorder factor σT and static disorder factor σS are 0.275 nm, 11.9, 0.006 9 nm, 0.034 nm; 0.215 nm， 2.7， 0.005 5 nm， 0.003 8 nm, and 0.276 nm, 12.4, 0.006 7 nm, 0.035 nm; 0.214 nm， 2.9， 0.005 8 nm， 0.004 2 nm for the Ni-Ni and Ni-B first neighbor shells of Ni-B and Ni-Ce-B ultrafine amorphous alloys, respectively. It is indicated that the σS of Ni-Ni shell is rather larger, about four or five times as large as that of σT, and one order larger than that of σS of Ni-B shell. Ni-B sample is crystallized after being annealed at 300 ℃, and its RNi—Ni as well as σS are 0.254 nm and 0.011 nm, respectively. However, the crystallization temperature of Ni-Ce-B sample increases about 100 ℃ due to the addition of 0.3% Ce element. The local structure around Ni atom for the Ni-B sample annealed at 500 ℃ is fully similar to that of Ni foil. For the Ni-Ce-B samples annealed at 500 ℃, the σS of Ni-Ni shell is 0.007 3 nm and the N of Ni-B shell is 1.2. It implies that the Ni lattice produced from the crystallization of Ni-Ce-B amorphous alloys is significantly distorted and the interaction between Ni and B atoms is strongly increased by the effect of Ce element.