  CrAs was firstly observed possessing the bulk superconductivity (Tc~2 K)
under high pressure (0.8 GPa) in the very recent work (Wei Wu, et al. Nature
Communications 5, 5508 (2014)). To explore the correlation between the
structure and the superconductivity, the high-pressure structure evolution of
CrAs was investigated using angle dispersive X-ray diffraction (XRD) method
with small steps of ~0.1 GPa in a diamond anvil cell (DAC) up to 1.8 GPa. In
the pressure range covered by our current experiment, the structure of CrAs
keeps stable. However, the lattice parameters exhibit anomalous compression
behaviors. With the pressure increasing, the lattice parameters a and c both
show a process of first increasing and then decreasing, and the lattice
parameter b goes through a quick contract at 0.35 GPa, which suggests a
pressure-induced isostructural phase transition occurs in CrAs around this
pressure point. Above the phase transition pressure, the axial
compressibilities of CrAs present remarkable anisotropy. The compressibilities
along the a- and c-axis are about an order of magnitude smaller than that along
the b-axis, which is closely related to the different stacking modes in CrAs6
octahedron along different crystallographic axes. A schematic band model was
used for addressing above anomalous compression behavior in CrAs.
