The interest in ferroelectric van der Waals crystals arises from the potential to realize ultrathin ferroic systems owing to the reduced surface energy of these materials and the layered structure that allows for exfoliation. Here, we reveal giant negative electrostriction of van der Waals layered copper indium thiophosphate (CIPS), with an electrostrictive coefficient Q33 as high as -3.2 m$^{4}$/C$^{2}$ and the resulting bulk piezoelectric coefficient d$_{33}$ of -85 pm/V. As a result, the electromechanical response of CIPS is comparable in magnitude to established perovskite ferroelectrics despite possessing a much smaller spontaneous polarization of only a few $\mu$C/cm$^{2}$. Moreover, in the paraelectric state, readily accessible owing to low transition temperature, CIPS exhibits large dielectric tenability, similar to widely-used barium strontium titanate, and as a result both giant and continuously tunable electromechanical response. The persistence of electrostrictive and tunable responses in the paraelectric state indicates that even few layer films or nanoparticles will sustain significant electromechanical functionality, offsetting the inevitable suppression of ferroelectric properties in the nanoscale limit. These findings can likely be extended to other ferroelectric transition metal thiophosphates and (quasi-) two-dimensional materials and might facilitate the quest towards novel ultrathin functional devices incorporating electromechanical response.

翻译：由于这些材料的地表能量减少,而且能够进行排泄。在这里,我们揭示了Van der Waals 层铜层硫磷酸盐(CIPS)的极负电压,其电压系数为Q33至-3.2 m ⁇ 4 美元/C ⁇ 2}美元,其结果为 - 85 pm/V。 其结果是,CIPS的电动机械反应相当于已经建立的极易腐铁电离层结构。 尽管Van der Waals 层铜层硫酸盐(CIPS)的自发电压极低,其电压系数为Q33至-3.2 m m ⁇ 4 美元/C ⁇ 2}美元,其结果为 - 85 pm/V。 因此,CIPS的电机能反应在数量上与已经建立起来的超压铁层电流能反应是相当的。 在钢铁层中,电压层的电解和金枪鱼反应可能会持续到不可避免的铁层。