A new hydrous phase δ-AlOOH synthesized at 21 GPa and 1000 °C

Abstract

 A new phase of AlOOH (tentatively called δ-AlOOH) was synthesized at 21 GPa and 1000 °C and its crystal structure was identified by a powder X-ray diffraction method. Rietveld refinement revealed that this aluminum oxide hydroxide has an orthorhombic unit cell, a = 4.7134(1) Å, b = 4.2241(1) Å, c = 2.83252(8) Å, V = 56.395 (5) ų, and Z = 2 in the space group of P2₁ nm. A calculated density is 3.533 g cm⁻³, which is about 4.48 and 15.04% denser than that of diaspore and boehmite, respectively. The δ-[Al_0.86Mg_0.07Si_0.07]OOH is also stable at 21 GPa and 1000 °C, coexisting with majorite and phase egg, and its cell parameters are a = 4.710(1) Å, b = 4.215(1) Å, c = 2.839(1) Å, and V = 56.37(1) ų.