Phase transition in silver niobate under high pressures

As an emerging antiferroelectric material, ${\mathrm{AgNbO}}₃$ holds promise in various applications like sensors, high-density data storage, and energy conversion. Understanding its structural behavior under high pressure is vital for establishing a phase diagram, which is of importance for properties design of antiferroelectric materials. However, the detailed phase structures of representative ${\mathrm{AgNbO}}₃$ under high pressures were still under debate. Hence, we investigated high-pressure structural evolution of ${\mathrm{AgNbO}}₃$ using Raman spectroscopy, in situ high-pressure synchrotron x-ray diffraction, and ab initio density-functional theory. The results revealed a transition path of $Pbcm\ensuremath{\rightarrow}Cmcm\ensuremath{\rightarrow}Pm\overline{3}m$ with the increases of pressures. The ${\mathrm{AgNbO}}₃$ initially exhibited an orthorhombic structure with the Pbcm space group at ambient pressure, transitioning to Cmcm at 5.83 GPa. With further pressure increasing to 9.89 GPa, a second cubic phase with the $Pm\overline{3}m$ space group could be observed. The coexistence of Cmcm and $Pm\overline{3}m$ phases transformed into a pure $Pm\overline{3}m$ structure at around 16.71 GPa. Ab initio density-functional theory validated the phase transition path with high pressures. The structural transformations were mainly driven by the pressure-induced movement of Ag ions and oxygen octahedron rotations. These findings carry significant implications for the design and optimization of devices operating under high pressures.