Structural and magnetic orders in the new high pressure corundum derivative Fe2LiNbO6

LiNbO3 (lithium niobate, R3c space group) where Li/Nb cation order in the corundum arrangment) breaks inversion symmetry giving rise to important electro-optic, ferroelectric and piezoelectric effects. Iron-doped lithium niobate is of great interest because of photorefractive properties and photochromism, however, Fe2O3 doping is limited to 11 mol% at ambient conditions so we have explored high-pressure high-temperature syntheses to expand this limit. We have discovered that an almost single phase 1 Fe2O3:1 LiNbO3 material can be prepared at high-pressure. Neutron diffraction is needed to compare possible R3c and R-3c structural models for Fe2LiNbO6 and determine which gives the best description, also providing bond distances and cation populations if two sites are present in the R3c type. Fe2LiNbO6 show two successive magnetic transitions at TC1 ~120 K and at TC2 ~30 K, and Mossbauer spectroscopy confirms Fe3+ spin order at 4 K. Neutron diffraction is therefore also needed to solve the magnetic structure and explore its thermal evolution. Fe2LiNbO6 will be of great interest for multiferroic properties if confirmed to have both polar R3c symmetry and spin order at low temperatures.