Study on Paramagnetic Interactions of (CH3NH3)2CoBr4 Hybrid Perovskites Based on Nuclear Magnetic Resonance (NMR) Relaxation Time.

Ae Ran Lim,Sun Ha Kim

doi:10.3390/molecules24162895

Abstract

The thermal properties of organic–inorganic (CH3NH3)2CoBr4 crystals were investigated using differential scanning calorimetry and thermogravimetric analysis. The phase transition and partial decomposition temperatures were observed at 460 K and 572 K. Nuclear magnetic resonance (NMR) chemical shifts depend on the local field at the site of the resonating nucleus. In addition, temperature-dependent spin–lattice relaxation times (T1ρ) were measured using 1H and 13C magic angle spinning NMR to elucidate the paramagnetic interactions of the (CH3NH3)+ cations. The shortening of 1H and 13C T1ρ of the (CH3NH3)2CoBr4 crystals are due to the paramagnetic Co2+ effect. Moreover, the physical properties of (CH3NH3)2CoBr4 with paramagnetic ions and those of (CH3NH3)2CdBr4 without paramagnetic ions are reported and compared.

Highlights

Hybrid organic–inorganic compounds based on perovskite structures are currently attracting an increased amount of interest owing to their potential as substitutes for perovskite solar cells [1,2,3,4,5,6,7,8,9,10]
The present study was conducted to investigate the thermodynamic properties of the phase transition temperature, thermal property, and paramagnetic interactions of (CH3NH3)2CoBr4 (CH3 NH3 )2 CoBr4 crystal using differential scanning calorimetry (DSC), thermogravimetric analysis have not been studied in full
The thermal properties and phase transition temperature of (CH3 NH3 )2 CoBr4 crystals grown based on the slow evaporation method were investigated with Thermogravimetric analysis (TGA), DSC, and optical polarizing microscopy

Summary

Introduction

Hybrid organic–inorganic compounds based on perovskite structures are currently attracting an increased amount of interest owing to their potential as substitutes for perovskite solar cells [1,2,3,4,5,6,7,8,9,10]. Mare located in the tetrahedral structure formed by the halogen ions X, and lie in the planes bridged by the (CH3 NH3 )+ cations [12] These crystals have a layered structure and exhibit quasi-, two-dimensional magnetic properties. The (CH3 NH3 ) CoBr4 crystal structure has monoclinic symmetry and belongs to the space group P21 /c, with lattice constants a = 7.9782 Å, b = 13.1673 Å, c = 11.2602 Å, and ß = 96.3260◦ [14]. The phase transition temperature, thermal property, and paramagnetic interactions of (CH3 NH3 ) CoBr4 have not been studied in full. The paramagnetic ions of Molecules 2019, 24, x the lead-free perovskite are eco-friendly, which is important for application to solar cells. The present study was conducted to investigate the thermodynamic properties of the phase transition temperature, thermal property, and paramagnetic interactions of (CH3NH3)2CoBr4. Anomaly at (CH (=T3C))2in the4DSC is related to the transition

NH occurs at approximately

Differential scanning calorimetry

H into ms at

Recovery traces for 1 H-NMR

Materials and Methods

Conclusions