Dimensional crossover-induced polarization boost in layered perovskite Ca2Nb2O7 under high pressure

In recent years, dimensional engineering in perovskites has attracted considerable interest as an effective strategy to tailor their optical and electrical properties. However, conventional chemical doping inherently modifies the material composition, complicating the fundamental understanding of intrinsic dimensional effects on perovskite properties. Here, taking the layered perovskite Ca2Nb2O7 as a model, we showcase the observation of a mechanical pressure-induced dimensional transition from a two-dimensional layered perovskite to a denser three-dimensional defective perovskite structure across a distinct two-phase coexistence region ranging from 12 to 18 GPa, employing in situ high-pressure x-ray diffraction experiments in conjunction with first-principles calculations. Notably, our comprehensive high-pressure single-crystal property measurements reveal that the structural densification results in approximately a 20% bandgap reduction, over two orders of magnitude decrease in the electrical transport anisotropy factor, and a threefold enhancement of ferroelectric remanent polarization. Our results establish a viable approach for achieving composition-preserving dimensional transitions in perovskites and provide key insights into the structure–property evolution of layered perovskites under extreme pressure.