Li Kai, Li Zhi-Gang, Xu Jun, Qin Yan, Li Wei, Stroppa Alessandro, Butler Keith T, Howard Christopher J, Dove Martin T, Cheetham Anthony K, Bu Xian-He
School of Materials Science and Engineering & Tianjin Key Laboratory of Metal and Molecule-Based Material Chemistry, Nankai University, Tianjin 300350, China.
CNR-SPIN, c/o Dip. to di Scienze Fisiche e Chimiche, Università degli Studi dell'Aquila, Via Vetoio, 67100 Coppito (AQ), Italy.
J Am Chem Soc. 2022 Jan 19;144(2):816-823. doi: 10.1021/jacs.1c10188. Epub 2022 Jan 10.
Hybrid organic-inorganic perovskite (HOIP) ferroelectrics are attracting considerable interest because of their high performance, ease of synthesis, and lightweight. However, the intrinsic thermodynamic origins of their ferroelectric transitions remain insufficiently understood. Here, we identify the nature of the ferroelectric phase transitions in displacive [(CH)NH][Mn(N)] and order-disorder type [(CH)NH][Mn(HCOO)] via spatially resolved structural analysis and lattice dynamics calculations. Our results demonstrate that the vibrational entropy change of the extended perovskite lattice drives the ferroelectric transition in the former and also contributes importantly to that of the latter along with the rotational entropy change of the A-site. This finding not only reveals the delicate atomic dynamics in ferroelectric HOIPs but also highlights that both the local and extended fluctuation of the hybrid perovskite lattice can be manipulated for creating ferroelectricity by taking advantages of their abundant atomic, electronic, and phononic degrees of freedom.
有机-无机杂化钙钛矿（HOIP）铁电体因其高性能、易于合成和重量轻而备受关注。然而，其铁电转变的内在热力学起源仍未得到充分理解。在这里，我们通过空间分辨结构分析和晶格动力学计算，确定了位移型[(CH)NH][Mn(N)]和有序-无序型[(CH)NH][Mn(HCOO)]中铁电相变的性质。我们的结果表明，扩展钙钛矿晶格的振动熵变驱动了前者的铁电转变，并且与A位的旋转熵变一起，对后者的铁电转变也有重要贡献。这一发现不仅揭示了铁电HOIPs中微妙的原子动力学，还突出了杂化钙钛矿晶格的局部和扩展涨落都可以通过利用其丰富的原子、电子和声子自由度来操纵以产生铁电性。
