Nowok Andrzej, Sobczak Szymon, Roszak Kinga, Szeremeta Anna Z, Mączka Mirosław, Katrusiak Andrzej, Pawlus Sebastian, Formalik Filip, Barros Dos Santos Antonio José, Paraguassu Waldeci, Sieradzki Adam
Laboratoire National des Champs Magnétiques Intenses, EMFL, CNRS UPR 3228, Université Toulouse, INSA-T, Toulouse, France.
Department of Experimental Physics, Wrocław University of Science and Technology, Wrocław, Poland.
Nat Commun. 2024 Aug 31;15(1):7571. doi: 10.1038/s41467-024-51396-5.
Three-dimensional organic-inorganic perovskites are rapidly evolving materials with diverse applications. This study focuses on their two representatives - acetamidinium manganese(II) formate (AceMn) and formamidinium manganese(II) formate (FMDMn) - subjected to varying temperature and pressure. We show that AceMn undergoes atypical pressure-induced structural transformations at room temperature, increasing the symmetry from ambient-pressure P2/n phase II to the high-pressure Pbca phase III. In turn, FMDMn in its C2/c phase II displays temperature- and pressure-induced ordering of cage cations that proceeds without changing the phase symmetry or energy barriers. The FMD cations do not order under constant volume across the pressure-temperature plane, despite similar pressure and temperature evolution of the unit-cell parameters. Temperature and pressure affect the cage cations differently, which is particularly pronounced in their relaxation dynamics seen by dielectric spectroscopy. Their motion require a rearrangement of the metal-formate framework, resulting in the energy and volumetric barriers defined by temperature-independent activation energy and activation volume parameters. As this process is phonon-assisted, the relaxation time is strongly temperature-dependent. Consequently, relaxation times do not scale with unit-cell volume nor H-bond lengths in formates, offering the possibility of tuning their electronic properties by external stimuli (like temperature or pressure) even without any structural changes.
三维有机-无机钙钛矿是一类快速发展且具有多种应用的材料。本研究聚焦于它们的两种代表物——甲酸乙脒锰（II）（AceMn）和甲酸甲脒锰（II）（FMDMn）——在不同温度和压力下的情况。我们发现，AceMn在室温下会经历非典型的压力诱导结构转变，对称性从常压下的P2/n相II增加到高压下的Pbca相III。相反，处于C2/c相II的FMDMn表现出温度和压力诱导的笼状阳离子有序化，且该过程不会改变相对称性或能垒。尽管晶胞参数的压力和温度演变相似，但在整个压力-温度平面上，FMD阳离子在恒容条件下不会发生有序化。温度和压力对笼状阳离子的影响不同，这在介电谱观察到的它们的弛豫动力学中尤为明显。它们的运动需要金属-甲酸盐骨架的重排，从而导致由与温度无关的活化能和活化体积参数定义的能量和体积能垒。由于这个过程是声子辅助的，弛豫时间强烈依赖于温度。因此，弛豫时间与晶胞体积或甲酸盐中的氢键长度无关，这使得即使在没有任何结构变化的情况下，也有可能通过外部刺激（如温度或压力）来调节它们的电子性质。
