Extremely promising monolayer materials with robust ferroelectricity and extraordinary piezoelectricity: δ-AsN,...

Low-dimensional ferroelectric materials, the mainstay of current high-density non-volatile memory devices, sensors, and nanoscale electronics, have attracted tremendous attention recently. Through employing an evolutionary algorithm and first-principles calculations, we report three novel and stable two-dimensional (2D) ferroelectric materials δ-AsN, δ-SbN, and δ-BiN with spontaneous polarization of up to 5.72 × 10^-10, 5.20 × 10^-10, and 4.45 × 10^-10 C m^-1, respectively. The ab initio molecular dynamics (AIMD) simulations further show that the failure temperature of ferroelectricity of δ-AsN, δ-SbN, and δ-BiN is as high as 2000 K, 2000 K, and 1700 K, demonstrating their strong robustness. More interestingly, the three novel materials also exhibit extraordinary piezoelectricity with relaxation ion piezoelectric coefficients d₁₁ of 5.39, 19.55, and 43.87 pm V^-1, respectively. The external strain effect found can effectively modulate their spontaneous polarization, ferroelectric switching energy barrier, and piezoelectric properties. These fascinating ferroelectricity and piezoelectricity features endow δ-AsN, δ-SbN, and δ-BiN with significant potential application in future miniaturized and integrated multi-functional electronic devices.