High-Pressure Vibrational and Structural Properties of Ni 3 V 2 O 8 and Co 3 V 2 O 8 up to 20 GPa.

The vibrational and structural behaviors of Ni 3 V 2 O 8 and Co 3 V 2 O 8 orthovanadates have been studied up to around 20 GPa by means of X-ray diffraction, Raman spectra, and theoretical simulations. Both materials crystallize in an orthorhombic Kagomé staircase structure (space group: Cmca ) at ambient conditions, and no phase transition was found in the whole pressure range. In order to identify the symmetry of the detected Raman-active modes under high pressure, single crystal samples of those materials were used in a polarized Raman and infrared setup. Moreover, high-pressure powder X-ray diffraction measurements were performed for Co 3 V 2 O 8 , and the results confirmed the structure stability also obtained by other diagnostic techniques. From this XRD analysis, the anisotropic compressibilities of all axes were calculated and the unit-cell volume vs pressure was fitted by a Birch-Murnaghan equation of state, obtaining a bulk modulus of 122 GPa.