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

TL;DR

This study investigates high-pressure structural phase transitions in ZnGa2O4 using in situ x-ray diffraction, revealing two transformations and providing detailed equations of state for different phases.

Contribution

It reports the first detailed high-pressure phase diagram and equations of state for ZnGa2O4, including the cubic, tetragonal, and orthorhombic structures, and compares them with related spinels.

Findings

Two structural phase transitions at 31.2 GPa and 55 GPa.

Determined equations of state for cubic and tetragonal phases.

ZnGa2O4 is among the less compressible spinels.

Abstract

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: V0 = 580.1(9) A3, B0 = 233(8) GPa, B0'= 8.3(4), and B0''= -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: V0 = 257.8(9) A3, B0 = 257(11) GPa, B0'= 7.5(6), and B0''= -0.0764 GPa-1 (implied value). The reported structural sequence coincides with that found in NiMn2O4 and MgMn2O4.