High‐pressure behaviour and phase transition of jadarite, a promising B and Li mineral commodity

The high-pressure behavior of a natural jadarite (ideally LiNaSiB3O7(OH), a∼6.76 Å, b∼13.80Å, c∼7.69 Å, β=124.09◦, space group P21/c) has been studied by in situ single-crystal and powder synchrotron X-ray diffraction up to 20 GPa, with a diamond anvil cell and using He as a hydrostatic pressure-transmitting fluid. Between 16.57(5) and 17.04(5) GPa, jadarite undergoes a first-order isosymmetric phase transition, which is reconstructive in character, with a ΔV of approximately -3%. The structure of the high-pressure polymorph was solved and refined (to R1 ∼ 4%). The isothermal bulk modulus of the low-P polymorph of jadarite is KV0 = 55.0(5) GPa (βV0 = 0.0182(2) GPa–1), and its P-derivative is 3.84(9). The compressional anisotropy, derived along the three main crystallographic directions, is modest, with βa0:βb0:βc0 = 1.23:1:1.23. The P-induced deformation mechanisms at the atomic scale, which lead to phase transition, are described.