Characterization of Calcium Hexaboride nano-scale Powder

Calcium hexaboride (CaB6) belongs to the refractory metal-like anaerobic compound and has a cubic crystal structure a (two 0.4 1 4 5 n m ). In addition to high melting point, high hardness, high strength and high chemical stability, it also has many special functions, such as constant specific resistance, zero thermal expansion value in a certain temperature range, high neutron absorption coefficient and low The electronic work function, these excellent performance determines its broad application prospects in various device components of modern technology. Therefore, many countries have conducted research on such materials. The characterization of CaB6 crystal structure has an important theoretical value for explaining its special physical properties. At present, the characterization of micro- and sub-micro-scale CaB6 powder has been reported. However, Ca B for nanometer scale. There are still few studies on powders. This paper describes the size, morphology and structure of nano-sized CaB6 powders. The degree of crystallization of nanometer powder in chemical synthesis is a difficult parameter to control. Due to the high activity of nanocrystals, the grains tend to have regular and random arrangement and grain size changes, that is, the transition between crystalline and non-crystalline is very active. Figure 3 shows a high-resolution plot of the grain of the particle pointed to by arrow C in Figure 3 (a). It can be clearly seen that there are three regions of one-dimensional atomic arrangement, two-dimensional lattice arrangement and non-crystalline arrangement in the same crystal grain. Even in a neatly arranged crystallographic map, there is a defect in the arrangement of the atoms. Figure 3 “ ) shows the Fourier transform diagram after removing the noise interference from the box area in Figure 3 (e). It can be seen that there are defects such as edge dislocations and screw dislocations in the lattice arrangement, which is also related to nanometers. It is related to the instability of crystal. For the existence of one-dimensional, two-dimensional and amorphous distribution in the grain structure of CaB6 powder, it can be explained by the following mechanism: In the chemical synthesis of CaB6, in the initial stage, the atoms are randomly arranged, with the prolongation of the holding time. These amorphous atoms form a two-dimensional regularly arranged crystal nucleus, and these nucleus grow to form nanocrystals. However, at the edge of the nanocrystal and the grain boundary, the activity of the nanocrystal is high, so that Incomplete crystal or amorphous phenomenon.

Characterization of Calcium Hexaboride nano-scale Powder