Equation of state of elbaite at high pressure up to 21.1 GPa and room temperature

The equation of the state of a natural elbaite sample has been investigated at room temperature and up to 21.1 GPa for the first time using in situ synchrotron X-ray diffraction in this study. No phase transition is observed on elbaite over the experimental pressure range. The pressure–volume data were fitted by the third-order Birch-Murnaghan equation of state (EoS) with the zero-pressure unit-cell volume V 0 = 1540.7 (6) Å 3 , the zero-pressure bulk modulus K T 0 = 114.7 (7) GPa, and its pressure derivative K ' T0 = 4.2 (1), while obtained V 0 = 1540.1 (4) Å 3 and K T0 = 116.4 (4) GPa when fixed K ' T0 = 4. Furthermore, the axial compressional behavior of elbaite was also fitted with a linearized third-order Birch-Murnaghan EoS, the obtained axial moduli for a -axis and c -axis are K a0 = 201 (4) GPa and K c0 = 60 (1) GPa, respectively. The axial compressibilities of a -axis and c -axis are β a = 1.66 × 10 –3 GPa −1 and β c = 5.56 × 10 –3 GPa −1 with an anisotropic ratio of β a : β c = 0.30: 1.00, which shows an intense axial compression anisotropy. The potential influencing factors on the bulk moduli and the anisotropic linear compressibilities of tourmalines were further discussed.