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 ev olutions of Ni-B and Ni-Ce-B ultrafine amorphous alloys prepared by chemica l reduction during the annealed process. The results show that the average bond length R-j, coordination number N, thermal disorder factor sigma (T) a nd static disorder factor sigmas 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 a nd Ni-B first neighbor shells of Ni-B and Ni-Ce-B ultrafine amorphous alloy s, respectively. It is indicated that the sigma (S) of Ni-Ni shell is rathe r larger, about four or five times as large as that of or, and one order la rger than that of as of Ni-B shell. Ni-B sample is crystallized after being annealed at 300 degreesC, and its RNi-Ni as well as sigma (S) are 0. 254 n m and 0. 011 nm, respectively. However, the crystallization temperature of Ni-Ce-B sample increases about 100 degreesC due to the addition of 0. 3% Ce element. The local structure around Ni atom for the NI-B sample annealed a t 500 degreesC is fully similar to that of Ni foil. For the Ni-Ce-B samples annealed at 500 degreesC, the sigma (S) of (Ni-Ni) shell is 0. 007 3 nm an d 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 ef fect of Ce element.