Phase transition in silver niobate under high pressures

As an emerging antiferroelectric material, AgNbO₃ 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 AgNbO₃ under high pressures were still under debate. Hence, we investigated high-pressure structural evolution of AgNbO₃ 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→Cmcm→Pm3̄m with the increases of pressures. The AgNbO₃ 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 Pm3̄m space group could be observed. The coexistence of Cmcm and Pm3̄m phases transformed into a pure Pm3̄m 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.