A detailed high pressure study is carried out on 1T′  MoTe2 using x-ray diffraction (XRD) and Raman spectroscopy measurements up to about 30.5 GPa along with a room temperature resistivity measurement up to 14.3(4) GPa and density functional theory calculations. Though high-pressure XRD measurements show no structural transition, all the lattice parameters exhibit anomalous changes in the pressure region 8.4 to 12.7 GPa. The compressibility of the sample is found to be reduced by almost four times above 12.7 GPa with respect to that below 8.4 GPa. The anomalies in the Raman mode corresponding to the out of plane vibrations of Mo atoms sitting in the unit cell surface indicate a strong electron–phonon coupling possibly mediated by differential strain inside the unit cell. A rapid decrease in resistivity value up to about 7.0(2) GPa of pressure agrees well with the increase in the density of states (DOS) at the Fermi energy with pressure. Pressure evolution of band structure, as well as DOS at the Fermi level, shows an enhancement of the metallic character of the sample. First principle calculations show increased stress in the x and y directions compared to the z-direction with the application of pressure.

Trirutile NiTa 2 O 6 has been studied under high pressure by in situ Raman and angle-dispersive synchrotron X-ray diffraction techniques. It undergoes a new quenchable phase at high pressures above 11.8 GPa accompanied by softening of the internal modes ν 1 (A 1g ), ν 1 (E g ), and ν 6 (E g ), and it is denser by 15% compared with its ambient phase. Various Raman-active modes of NiTa 2 O 6 diminished at high pressures due to the distortion of edge-sharing TaO 6 octahedra, which was further confirmed by Xray diffraction and density functional theory results. The equation of state has been determined using the second-order Birch− Murnaghan equation, and the obtained bulk modulus is 199(4) GPa. The pressure and volume dependence of optical lattice vibrational frequencies and their corresponding Gruneisen parameters are calculated, indicating the inconsistency of the trirutile structure at high pressures, which was accompanied by the strong deformation of TaO 6 octahedra. Pressure-induced structural metamorphosis and soft-mode-driven displacive transition related to the mechanical instability of NiTa 2 O 6 are examined and decompression results recommend the transition is irreversible.