In this work, we investigate the physical origin of ferroelectricity in monolayer ${\mathrm{Bi}}_2{\mathrm{TeO}}_5$ using first-principles theoretical approaches. It is revealed that the room-temperature ferroelectric order arises from the cooperative interplay between strong individual dipoles and moderate interdipole interactions. Based on the first-principles energy landscape, a phenomenological model is constructed to predict the temperature-dependent phase transition behavior via Monte Carlo simulations, in agreement with experimental observations. The finite-temperature results further indicate a small ferroelectric domain size, consistent with the moderate strength and relatively localized effective range of the interdipole interactions. Additionally, the experimentally observed antiferroelectriclike order induced by intercalated buffer layers is demonstrated to be a robustly pinned ${180}^{\circ }$ ferroelectric domain wall rather than a genuine antiferroelectric phase.

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• Ferroelectricity
• 2-dimensional systems
• First-principles calculations
• Materials modeling
• Metropolis algorithm
• Monte Carlo methods
• Multiscale modeling