Abstract
The VF3-type compound GaF3has been studied by high-pressure angle-dispersive X-ray diffraction in the pressure range from 0.0001 to 10 GPa. The compression mechanism was found to be highly anisotropic. Thec-axis shows little pressure dependence (≈0.4%), but exhibits negative linear compressibility up to ≈3 GPa where it achieves its maximum length. In contrast, the length of thea-axis is reduced by ≈8.8% at the highest measured pressure and an anomalous reduction in the linear compressibility is observed at 4 GPa. The zero pressure bulk modulusB0was determined toB0= 28(1) GPa. The compression mechanism of GaF3is discussed in terms of deformation of an 8/3/c2 sphere-packing model. The volume reduction of GaF3is mainly achieved through coupled rotations of the GaF6octahedra within the entire measured pressure range, which reduces the volume of the cubooctahedral voids. In addition, the volume of the GaF6octahedra also decreases forp≲ 4.0 GPa, but remains constant above this pressure. The volume reduction of the GaF6octahedra is accompanied by an increasing octahedral strain. Isosurfaces of the procrystal electron density are used for visualization of the cubooctahedral voids at different pressures.
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