Phase transition and compression of LiNbO3 under static high pressure

Lattice parameters of LiNbO3 were measured at room temperature over the pressure range 0–35 GPa by x-ray diffraction using the diamond anvil cell. In the region below 13 GPa (where a hydrostatic pressure was maintained) the pressure dependence of the volume can be well described by the Birch–Murnaghan equation of state, yielding B0=134±3 GPa for the zero-pressure bulk modulus and B′0 =2.9±0.5 for its pressure derivative. A phase transformation was detected at 30±3 GPa both by x-ray diffraction and by optical observation of the change from a transparent to an opaque state. The pattern of the high-pressure phase was tentatively indexed on the basis of a cubic cell with a=6.78 Å.