Structure and compressibility of synthetic ZnAl₂O₄ (gahnite) under high-pressure conditions, from synchrotron X-ray powder diffraction

The structural behavior of synthetic gahnite (ZnAl₂O₄) has been investigated by X-ray powder diffraction at high pressure (0-43 GPa) and room temperature, on the ID9 beamline at ESRF. The equation of state of gahnite has been derived using the models of Birch-Murnaghan, Vinet and Poirier-Tarantola, and the results have been mutually compared (the elastic bulk modulus and its derivatives versus P determined by the third-order Birch-Murnaghan equation of state are K₀ = 201.7(±0.9) GPa, K¹₀ = 7.62(±0.09) and K¹¹₀ = -0.1022 GPa^-1 (implied value). The compressibilities of the tetrahedral and octahedral bond lengths [0.00188(8) and 0.00142(5) GPa^-1 at P = O, respectively], and the polyhedral volume compressibilities of the four- and sixfold coordination sites [0.0057(2) and 0.0041 (2) GPa^-1 at P = O, respectively] are discussed.