Equation of state and structural phase transition in FeBO$\mathbf{_3}$ at high pressure

Evolution of X-ray diffraction patterns in FeBO$_3$ under high pressures up to 63 GPa has been investigated at room temperature in a diamond anvil cell. A structural phase transition at pressure of $53\pm2 \,$GPa was found for the first time. The transition is of the first- order type with the hysteresisless drop of the reduced unit cell volume of about 8.6%. Apparently, the transition is isostructural. At pressures below the transition, the equation of state for FeBO$_3$ was fitted. In approximation of the third order Birch-Murnagan equation of state, the bulk modulus $K$ and its first pressure derivative $K'$ were found to be $255 \pm25 \,$GPa and $5.0 \pm 1.2$, respectively.