Molybdenum borides including α-MoB₂ and β-MoB₂ have been successfully synthesized from boron and molybdenum at high pressure and high temperature (HPHT). The crystalline structures are confirmed by Rietveld refinements in the hexagonal (P6/mmm) and rhombohedral (R-3m) crystal systems for α- and β-MoB₂, respectively. The values of Vickers hardness (HV) are 15.2 GPa for α-MoB₂, which is firstly obtained, and 22.0 GPa for β-MoB₂. The hardness results for α- and β-MoB₂ are in good agreement with theoretical values calculated by first-principle calculations. The difference in hardness between α- and β-MoB₂ is attributed to the puckered quasi-3D (three dimensional) boron layers in β-MoB₂ which is confirmed by the calculated results of the Electron Localization Function (ELF) and elastic constants. These results are helpful to understand the hardness mechanism and to design superhard transition-metal borides (TMBs).

Raman spectroscopy, synchrotron angle-dispersive X-ray diffraction (ADXRD), first-principles calculations, and electrical resistivity measurements were carried out under high pressure to investigate the structural stability and electrical transport properties of metavanadate MgV₂O₆. The results have revealed the coordination change of vanadium ions (from 5+1 to 6) at around 4 GPa. In addition, a pressure-induced structure transformation from the C2/m phase to the C2 phase in MgV₂O₆ was detected above 20 GPa, and both phases coexisted up to the highest pressure. This structural phase transition was induced by the enhanced distortions of MgO₆ octahedra and VO₆ octahedra under high pressure. Furthermore, the electrical resistivity decreased with pressure but exhibited different slope for these two phases, indicating that the pressure-induced structural phase transitions of MgV₂O₆ was also accompanied by the obvious changes in its electrical transport behavior.

Recently, Ag₂Te was experimentally confirmed to be a 3D topological insulator (TI) at ambient pressure. However, the high-pressure behaviors and properties of Ag₂Te were rarely reported. Here, a pressure-induced electronic topological transition (ETT) is firstly found in Ag₂Te at 1.8 GPa. Before ETT, the positive pressure coefficient of bulk band-gap, which is firstly found in TIs family, is found by both first-principle calculations and in situ high-pressure resistivity measurements. The electrical resistivity obtained at room temperature shows a maximum at 1.8 GPa, which is nearly 3.3 times to that at ambient pressure. This result indicates that the best bulk insulating character and topological nature in Ag₂Te can be obtained at this pressure. Furthermore, the high-pressure structural behavior of Ag₂Te has been investigated by in situ high-pressure synchrotron powder X-ray diffraction technique up to 33.0 GPa. The accurate pressure-induced phase transition sequence is firstly determined as P2₁/c → Cmca → Pnma. It is worth noting that the reported isostructural P2₁/c phase is not existed and the reported structure of Cmca phase is corrected by CALYPSO methodology. The second high-pressure structure, a long puzzle to previous reports, is determined as Pnma phase. A pressure-induced metallization in Ag₂Te is confirmed by the results of temperature-dependent resistivity measurements.