In situ Raman spectroscopy and X-ray diffraction of pressure-induced phase transition in columbite CaNb2O6

Highlights: •The phase transition of CaNb2O6 was investigated for the first time under high pressure. •In situ Raman spectroscopy and Synchrotron X-ray diffraction were measured. •A pressure-induced reversible phase transition was observed below 23 GPa. •The orthorhombic columbite Pbcn transforms to monoclinic structure P21/c. •The lattice parameters of the new phase were obtained by the Pawley refinements. -- Abstract: The in situ high pressure studies of CaNb2O6 have been performed using Raman spectroscopy and Synchrotron X-ray diffraction in a DAC up to 23 GPa. Raman experiments show that most Raman peaks decrease in intensity and shift toward high wave numbers with increasing pressure. Two turn points in the slope of frequency–pressure curve of the slopes of Raman modes turn up at the pressure around 8 and 15 GPa. ADXRD results display that the old peaks disappear and some new peaks appear above 9.4 GPa, and the patterns remain unchanged above 15 GPa. Both Raman and X-ray diffraction data provide evidence of a reversible phase transition beginning from about 8 GPa and completing at 15 GPa