High-pressure and high-temperature structure and equation of state of Na3Ca2La(CO3)(5) burbankite

In this study we report the synthesis of single crystals of burbankite, Na3Ca2La(CO3)(5), at 5 GPa and 1073 K. The structural evolution, bulk modulus and thermal expansion of burbankite were studied and determined by two separate high-pressure (0-7.07(5) GPa) and high-temperature (298-746 K) in situ single-crystal X-ray diffraction experiments. The refined parameters of a second-order Birch-Murnaghan equation of state (EoS) are V-0 = 593.22(3) angstrom(3) and K-T0 = 69.8(4) GPa. The thermal expansion coefficients of a Berman-type EoS are alpha(0) = 6.0(2) x 10(-5) K-1, alpha(1) = 5.7(7) x 10(-8 )K(-2 )and V-0 = 591.95(8) angstrom(3). The thermoelastic parameters determined in this study allow us to estimate the larger density of burbankite in the pressure-temperature range of 5.5-6 GPa and 1173-1273 K, with respect to the density of carbonatitic magmas at the same conditions. For this reason, we suggest that burbankite might fractionate from the magma and play a key role as an upper-mantle reservoir of light trivalent rare earth elements (REE3+).