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

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.