Progress in functional studies of transition metal borides*

Abstract

In recent years, transition metal borides (TMBs) have attracted much attention because they are considered as potential superhard materials and have more abundant crystal structures compared with traditional superhard materials. So far, however, no superhard materials have been found in TMBs. A large number of structures and potential new properties in TMBs are induced by the various hybridization ways of boron atoms and the high valence electrons of transition metals, which provide many possibilities for its application. And most TMBs have layered structures, which make TMBs have the potential to be a two-dimensional (2D) material. The 2D materials have novel properties, but the research on 2D TMBs is still nearly blank. In this paper, the research progress of TMBs is summarized involving structure, mechanical properties, and multifunctional properties. The strong covalent bonds of boron atoms in TMBs can form one-dimensional, twodimensional, and three-dimensional substructures, and the multiple electron transfer between transition metal and boron leads to a variety of chemical bonds in TMBs, which are the keys to obtain high hardness and multifunctional properties of TMBs. Further research on the multifunctional properties of TMBs, such as superconductors, catalysts, and high hardness ferromagnetic materials, is of great significance to the discovery of new multifunctional hard materials.

Mechanical properties and multifunctionality of AlB2-type transition metal diborides *

“…High critical temperature (Tc) is always an unwearied goal for superconductors which also occupies an important stage in condensed matter physics and materials science. Compounds with light elements are easily to achieve this target because they can offer high Debye frequency, which is beneficial for the high Tc according to the Bardeen-Cooper-Schrieffer theory [32,43,[97][98][99][100][101][102][103][104][105][106][107][108]. The discovery of MgB 2 in 2001 leading to a flurry of researches about TMdBs due to its special crystal structure same to MgB 2 [103].…”

Effect of carbon doping on the structure and superconductivity in AlB2‐type (Mo0.96Ti0.04)0.8${(\text{Mo}_{0.96}\text{Ti}_{0.04})}_{0.8}$B2

“…Transition metal diborides (TMDBs) have attracted a lot of attention over the past few decades due to their diverse properties, [1][2][3] including high hardness and shear strength, [4][5][6][7] excellent corrosion resistance, 8,9 superior catalytic performance, 10,11 notrivial band topology, 12,13 high electrical conductivity and even superconductivity. [14][15][16][17][18] Among existing TMDBs, molybdenum diboride is unique in that it exists in both hexagonal AlB 2 -type and rhombohedral structures.…”

Effect of carbon doping on the structure and superconductivity in AlB$_{2}$-type (Mo$_{0.96}$Ti$_{0.04}$)$_{0.8}$B$_{2}$

“…Transition metal diborides (TMDBs) have attracted a lot of attention over the past few decades due to their diverse properties [1][2][3], including high hardness and shear strength [4][5][6][7], excellent corrosion resistance [8,9], superior catalytic performance [10,11], notrivial band topology [12,13], high electrical conductivity and even superconductivity [14][15][16][17][18]. Among existing TMDBs, molybdenum diboride is unique in that it exists in both hexagonal AlB 2 -type and rhombohedral structures [19].…”