High pressure X-ray diffraction study of potassium azide

Crystal structure and compressibility of potassium azide was investigated by in-situ synchrotron powder X-ray diffraction in a diamond anvil cell at room temperature up to 37.7 GPa. In the body-centered tetragonal (bct) phase, an anisotropic compressibility was observed with greater compressibility in the direction perpendicular to the plane containing N 3 − ions than directions within that plane. The bulk modulus of the bct phase was determined to be 18.6(7) GPa. A pressure-induced phase transition may occur at 15.5 GPa. ► Potassium azide (KN 3) exhibits anisotropic compressibility under pressure with the direction between N 3 − planes more compressible than that within planes. ► Third-order isothermal equation of state of the body-centered tetragonal phase is determined to be K (bulk modulus)=18.6(7) GPa with K′ (pressure derivative of bulk modulus)= 6.7(4). ► Phase transition may occur at 15.5 GPa.