NMR and Raman Scattering Studies of Temperature- and Pressure-Driven Phase Transitions in CH₃NH₂NH₂PbCl₃ Perovskite

Abstract

Three-dimensional methylhydrazinium (CH3NH2NH2 +, MHy+) lead halides, related to the famous methylammonium (CH3NH3 +, MA+) and formamidinium (CH­(NH2)2 +, FA) perovskites, are attractive optoelectronic materials crystallizing in polar structures. In this work, temperature-dependent 1H and 207Pb magic-angle spinning (MAS) NMR, Raman as well as high-pressure Raman studies of CH3NH2NH2PbCl3 (MHyPbCl3) are reported. Raman spectroscopy reveals many similarities between phonon properties of MHy lead halides and the MA and FA analogues. In particular, these families of compounds show an increase in wavenumber of cage modes when large I– ions are replaced by smaller Br– and then Cl– ones. They also show strong sensitivity of the CH3 torsional mode on size of the cavity occupied by MHy+ cation that decreases with decreasing size of the halide anion. The cage modes of MHyPbCl3 are, however, observed at significantly lower wavenumbers than similar modes of MAPbCl3 and FAPbCl3, indicating higher softness of MHyPbCl3. Temperature-dependent Raman and NMR studies demonstrate that the MHy+ cations in MHyPbCl3 are significantly less affected by the temperature-induced phase transition than the Pb–Cl framework. This suggests a displacive type of the phase transition dominated by tilting and deformation of the PbCl6 octahedra. Analysis of the 207Pb MAS NMR spectra reveals the presence of two differently distorted PbCl6 octahedra and diminishing (increasing) distortion of the less (more) distorted octahedra in the high-temperature phase. Pressure-dependent Raman studies reveal the presence of a single first-order pressure-induced phase transition between 0.72 and 1.27 GPa. Analysis of the spectra indicates that the driving forces for the pressure-induced phase transition in MHyPbCl3 are tilting and distortion of the PbCl6 octahedra accompanied by reorientation of MHy+ cations. Raman spectra do not show evidence of any additional phase transition or amorphization up to 6.95 GPa.

Mechanism of Unusual Isosymmetric Order-Disorder Phase Transition in [Dimethylhydrazinium]Mn(HCOO)3 Hybrid Perovskite Probed by Vibrational Spectroscopy

“…The remaining stretching vibrations, νasCNC, νsCNC and νNN, are located in the 990-1002, 820-832 and 1089-1098 cm −1 range, respectively. The position of the νsCNC bands is in good agreement with previous studies, i.e., this band was observed at 874 cm −1 for [MHy]Mn(HCOO)3 [20], 877 cm −1 for [MHy]Mn(H2POO)3 [42], 868 and 871 cm −1 for [MHy]PbBr3 [43] and 881 cm −1 for [MHy]PbCl3 [44]. The antisymmetric counterpart was previously observed at 1010 cm −1 for [MHy]Mn(H2POO)3 [42], 1004 cm −1 for [MHy]PbBr3 [43] and 1011 cm −1 for [MHy]PbCl3 [44].…”

“…The position of the νsCNC bands is in good agreement with previous studies, i.e., this band was observed at 874 cm −1 for [MHy]Mn(HCOO)3 [20], 877 cm −1 for [MHy]Mn(H2POO)3 [42], 868 and 871 cm −1 for [MHy]PbBr3 [43] and 881 cm −1 for [MHy]PbCl3 [44]. The antisymmetric counterpart was previously observed at 1010 cm −1 for [MHy]Mn(H2POO)3 [42], 1004 cm −1 for [MHy]PbBr3 [43] and 1011 cm −1 for [MHy]PbCl3 [44]. For the [MHy]Mn(HCOO)3 crystal, this vibration was assigned to bands observed near 1092 cm −1 [20], but our DFT and previous ab initio calculations [41] showed that bands observed in the 1089-1098 cm −1 range for [DMHy]Mn(HCOO)3 originate from νNN.…”

Interfaces in metal halide perovskites probed by solid-state NMR spectroscopy

“…In lead MHPs, the substantial chemical shi range of 207 Pb signals of up to 3000 ppm and peak widths (full-width-at-half-maximum, FWHM in the range of a fraction of kHz to several tens of kHz) provides a powerful way to characterize structural properties such as Pb-X distances, Pb-X-Pb bond angles and octahedral tilts in the PbX 6 octahedra. 304,314,[353][354][355]358,359 1D NMR oen suffices for identifying and distinguishing the local coordination spheres and the impact of A and X site doping on the 207 Pb and 119 Sn shis in ABX 6 MHPs. In addition, 2D 207 Pb exchange spectroscopy has been used to gain insight into the solid-solution behavior of MAPbX 3 (X ¼ Cl, Br, I) obtained from mechanochemical synthesis.…”

“…The environmental stability and degradation processes of a wide variety of 3D MHPs have been investigated by multinuclear ( 1 H, 207 Pb, 119 Sn, 133 Cs) ssNMR spectroscopy techniques. 312,313,359,367,368 The hydrothermal stability and degradation of MAPbI 3 has been characterized through 1D 207 Pb NMR spectroscopy, and revealed that pristine MAPbI 3 and its degradation products, MAPbI 3 $H 2 O, and PbI 2 , have distinct chemical shis (Fig. 7a).…”

The Contribution of NMR Spectroscopy in Understanding Perovskite Stabilization Phenomena

“…Furthermore, the proton T 1 is sensitive to phase transitions [ 26 , 27 ]. (ii) 13 C analysis, for detecting the incorporation of additives within the perovskite framework [ 28 ], for elucidating the phase composition at low temperatures [ 29 ] and for phase transition identification [ 30 ]. Both 1 H and 13 C spectra recorded at variable temperatures provide information useful for symmetry evaluation [ 31 ].…”