Post-spinel transformations and equation of state in ZnGa2O4: Determination at high pressure by in situ x-ray diffraction

Room-temperature angle-dispersive x-ray diffraction measurements on spinel ZnGa2O4 up to 56 GPa show evidence of two structural phase transformations. At 31.2 GPa, ZnGa2O4 undergoes a transition from the cubic spinel structure to a tetragonal spinel structure similar to that of ZnMn2O4. At 55 GPa, a second transition to the orthorhombic marokite structure (CaMn2O4-type) takes place. The equation of state of cubic spinel ZnGa2O4 is determined: V-0=580.1(9) A(3), B-0=233(8) GPa, B-0(')=8.3(4), and B-0(')=-0.1145 GPa(-1) (implied value); showing that ZnGa2O4 is one of the less compressible spinels studied to date. For the tetragonal structure an equation of state is also determined: V-0=287.8(9) A(3), B-0=257(11) GPa, B-0(')=7.5(6), and B-0(')=-0.0764 GPa(-1) (implied value). The reported structural sequence coincides with that found in NiMn2O4 and MgMn2O4.