Uncovering the crystallography and formation mechanism of nanoscale clusters in Sb-rich SPPs of a p-type (Bi, Sb)2Te3 alloy.

Considering that the crystallographic characteristics of the Sb-rich secondary phase particles (SPPs) greatly affect the thermoelectric properties of Bi2Te3 based materials, it is of great significance to explore the mechanism behind the Sb-rich SPPs in the p-type (Bi, Sb)2Te3 material. Here a conventional TEM technique was used to characterize the composition, size and distribution of Sb-rich SPPs in a spark plasma sintered p-type (Bi, Sb)2Te3 alloy. The results indicated that two different morphologies of Sb-rich SPPs including elongated and circular Sb-rich SPPs were frequently observed. Combined with high-resolution transmission electron microscopy, this work provides atomic-scale evidence for the formation mechanism behind the Sb-rich SPPs in the (Bi, Sb)2Te3 material.

Transitional structure of {0001} twin in a deformed p-type (Bi,Sb)2Te3 alloy: a direct experimental basis for understanding the twinning mechanism.

Twin boundaries provide a strong phonon scattering center to hinder the lattice thermal conductivity in thermoelectric materials, but the underlying evolution process of deformation twinning remains to be figured out. By applying atomic resolution transmission electron microscope (TEM) observations, a novel type of transitional structure of {0001} twin was observed, for the first time, in the p-type (Bi,Sb)2Te3 alloy subjected to three-point bending deformation. The transformation from matrix to (0001) twin can be realized by the following path: matrix → transitional twin → (0001) twin, and this process was completed by the gliding of a total of four partial dislocations (b1 = 1/3[011̄0]) extended in the different (0001) planes. This new finding here will shed light on the nucleation and growth of deformation twins in the p-type (Bi, Sb)2Te3 alloy.

Stacking faults in Zr(Fe, Cr)2 Laves structured secondary phase particle in Zircaloy-4 alloy.

Stacking faults (SFs) in secondary phase particles (SPPs), which generally crystallize in the Laves phase in Zircaloy-4 (Zr-4) alloy, have been frequently observed by researchers. However, few investigations on the nano-scale structure of SFs have been carried out. In the present study, an SF containing C14 structured SPP, which located at grain boundaries (GBs) in the α-Zr matrix, was chosen to be investigated, for its particular substructure as well as location, aiming to reveal the nature of the SFs in the SPPs in Zr-4 alloy. It was indicated that the SFs in the C14 structured SPP actually existed in the local C36 structured Laves phase, for their similarities in crystallography. The C14 → C36 phase transformation, which was driven by synchroshearing among the (0001) basal planes, was the formation mechanism of the SFs in the SPPs. By analyzing the strained regions near the SPP, a model for understanding the driving force of the synchroshear was proposed: the interaction between SPP and GB resulted in the Zener pinning effect, leading to the shearing parallel to the (0001) basal planes of the C14 structured SPP, and the synchroshear was therefore activated.

Considerable knock-on displacement of metal atoms under a low energy electron beam.

Under electron beam irradiation, knock-on atomic displacement is commonly thought to occur only when the incident electron energy is above the incident-energy threshold of the material in question. However, we report that when exposed to intense electrons at room temperature at a low incident energy of 30 keV, which is far below the theoretically predicted incident-energy threshold of zirconium, Zircaloy-4 (Zr-1.50Sn-0.25Fe-0.15Cr (wt.%)) surfaces can undergo considerable displacement damage. We demonstrate that electron beam irradiation of the bulk Zircaloy-4 surface resulted in a striking radiation effect that nanoscale precipitates within the surface layer gradually emerged and became clearly visible with increasing the irradiation time. Our transmission electron microscope (TEM) observations further reveal that electron beam irradiation of the thin-film Zircaly-4 surface caused the sputtering of surface α-Zr atoms, the nanoscale atomic restructuring in the α-Zr matrix, and the amorphization of precipitates. These results are the first direct evidences suggesting that displacement of metal atoms can be induced by a low incident electron energy below threshold. The presented way to irradiate may be extended to other materials aiming at producing appealing properties for applications in fields of nanotechnology, surface technology, and others.