High-pressure study of azurite Cu3(CO3)2(OH)2 by synchrotron radiation X-ray diffraction and Raman spectroscopy

Abstract

The high-pressure properties of natural azurite [Cu3(CO3)2(OH)2] have been investigated by in situ synchrotron powder X-ray diffraction and Raman spectroscopy up to 11 and 16 GPa at room temperature, respectively. The results indicate that azurite is stable within the pressure region in this study. The pressure–volume data from in situ X-ray diffraction experiments were described by a third-order Birch–Murnaghan equation of state with V 0 = 304.5 (4) A3, K 0 = 40 (2) GPa and K 0′ = 5.5 (6). The K 0 was obtained as 45.1 (8) GPa when K 0′ was fixed at 4. The axial compressional behavior of azurite was also fitted with a linearized third-order Birch–Murnaghan equation of state, showing an intense anisotropy with K a0 = 29.7 (9) GPa, K b0 = 25.0 (7) GPa and K c0 = 280 (55) GPa. In addition, the Raman spectroscopy of azurite in this study also presents the weak [OH]− group and the rigid [CO3]2− group. The different high-pressure behaviors of azurite and malachite combined with the smaller isothermal bulk modulus compared with certain anhydrous carbonates and the obvious compression anisotropy of azurite were discussed with the experimental results in this study together with the results from previous studies. Furthermore, the effect of hydroxyl on the high-pressure behaviors of carbonates was also discussed.