Structural Phase Transitions

Jeffrey, Kenneth R.; Penner, Glenn H.

doi:10.1002/9780470034590.emrstm1051

Cited by 3 publications

(4 citation statements)

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“…The kink in the 1 H T 1 at the T = 182 K phase transition suggests second order character. 48 Any features associated with the T = 162 K and 118 K phase transitions in the 1 H T 1 are too subtle to resolve. The 1 H T 1 and neutron MSD data demonstrate that the phase transitions of CH(NH 2 ) 2 PbBr 3 correlate to modulation of the dynamic degrees of freedom of CH(NH 2 ) 2 + .…”

Section: ■ Resultsmentioning

confidence: 99%

“…[29][30][31] At T = 265 K, CH(NH2)2PbBr3 transitions from the cubic perovskite phase to a tetragonal perovskite phase, 29,31 which appears as an anomaly in the MSD data in Figure 2b, and as a dip in the 1 H T1. This dip is ascribed to a convolution of the discontinuity caused by a first order transition 48 with magic angle spinning (MAS) induced temperature gradients. The MSD and 1 H T1 exhibit similar features at the T = 153 K tetragonal to orthorhombic phase transition.…”

Section: Cation Dynamics Of Ch(nh2)2pbbr3mentioning

confidence: 99%

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Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

et al. 2020

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Although initial studies on hybrid perovskites for photovoltaic applications focused on simple compositions, the most technologically relevant perovskites are heavily substituted. The influence of chemical substitution on the general phase behavior and specific physical properties remains ambiguous. The hybrid perovskite formamidinium lead bromide, CH(NH2)2PbBr3, exhibits complex phase behavior manifesting in a series of crystallographically-unresolvable phase transitions associated with changes in the cation dynamics. Here, we characterize the molecular and lattice dynamics of CH(NH2)2PbBr3 as a function of temperature, and their evolution upon chemical substitution of CH(NH2)2 + for cesium (Cs + ) with crystallography, neutron scattering, 1 H and 14 N nuclear magnetic resonance spectroscopy, and 79 Br nuclear quadrupolar spectroscopy. Cs + substitution suppresses the four low-temperature phase transitions of CH(NH2)2PbBr3, which propagate through concerted changes in the dynamic degrees of freedom of the organic sub-lattice and local or long-range distortions of the octahedral framework. We propose that cesium substitution suppress the phase transitions through the relief of geometric frustration associated ** Both authors contributed equally.with the orientations of CH(NH2)2 + molecules, which retain their local dynamical degrees of freedom.

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Section: ■ Resultsmentioning

confidence: 99%

Section: Cation Dynamics Of Ch(nh2)2pbbr3mentioning

confidence: 99%

Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

et al. 2020

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“…In solids that exhibit solid–solid phase transitions, the temperature dependence of the physical properties (e.g., lattice parameters, magnetic properties, electric field gradients) can often exhibit critical phenomena . For example, ν QS can be described by an equation of the form where T c is the phase transition temperature, a is here expressed in units of kilohertz, and n is the critical exponent. ,,,, Kawamura et al found that lattice parameters for the tetragonal phase of MAPbI 3 are proportional to ( T c – T ) n with n = 0.42 …”

Section: Nmr Backgroundmentioning

confidence: 99%

“…where T c is the phase transition temperature, a is here expressed in units of kilohertz, and n is the critical exponent. 2,11,15,59,60 were packed in 4 mm zirconia rotors; at 11.75 T, a Bruker 4 mm MAS probe was used to acquire the data, while at 21.1 T the rotor was placed into a 5 mm outer diameter glass tube and the spectra were acquired with a Bruker 5 mm H/X solenoid probe.…”

Section: ■ Introductionmentioning

confidence: 99%

Methylammonium Cation Dynamics in Methylammonium Lead Halide Perovskites: A Solid-State NMR Perspective

et al. 2018

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In light of the intense recent interest in the methylammonium lead halides, CHNHPbX (X = Cl, Br, and I) as sensitizers for photovoltaic cells, the dynamics of the methylammonium (MA) cation in these perovskite salts has been reinvestigated as a function of temperature via H,N, and Pb NMR spectroscopy. In the cubic phase of all three salts, the MA cation undergoes pseudoisotropic tumbling (picosecond time scale). For example, the correlation time, τ, for the C-N axis of the iodide salt is 0.85 ± 0.30 ps at 330 K. The dynamics of the MA cation are essentially continuous across the cubic ↔ tetragonal phase transition; however, H andN NMR line shapes indicate that subtle ordering of the MA cation occurs in the tetragonal phase. The temperature dependence of the cation ordering is rationalized using a six-site model, with two equivalent sites along the c-axis and four equivalent sites either perpendicular or approximately perpendicular to this axis. As the cubic ↔ tetragonal phase transition temperature is approached, the six sites are nearly equally populated. Below the tetragonal ↔ orthorhombic phase transition, H NMR line shapes indicate that the C-N axis is essentially frozen.

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A solid-state NMR investigation of the colossal expansion material, Ag₃Co(CN)₆

2012

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Presented here is a solid-state NMR investigation of the so-called “colossal expansion” material, Ag3Co(CN)6, a compound that exhibits some of the largest positive and negative thermal expansion properties reported. This study explores the 13C, 15N, and 59Co NMR properties of this material at room temperature and at variable temperatures with the goal of probing the effects of this colossal expansion behaviour on these properties. We found that the flexible nature of the crystal framework leads to a distribution of electric field gradients, and that, oddly enough, no strong correlation is observed between the NMR parameters of Ag3Co(CN)6 and its colossal expansion nature. The 59Co isotropic chemical shift increased and the 59Co nuclear quadrupolar coupling constant decreased with increasing temperature, but neither of these relationships were extraordinary when compared to other octahedral Co(III) complexes. The link between the colossal expansion and the NMR properties of Ag3Co(CN)6 may be the distribution of lattice parameters and hence unusually broad features in the 59Co NMR spectra. The high order of symmetry at the cobalt site resulted in a small quadrupolar coupling constant less than 1 MHz in magnitude. We also observed a |1J(107/109Ag,15N)| value of 96 Hz, the largest 107/109Ag–15N coupling constant reported to date.

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Structural Phase Transitions

Cited by 3 publications

References 67 publications

Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

Methylammonium Cation Dynamics in Methylammonium Lead Halide Perovskites: A Solid-State NMR Perspective

A solid-state NMR investigation of the colossal expansion material, Ag₃Co(CN)₆

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Structural Phase Transitions

Cited by 3 publications

References 67 publications

Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

Cesium Substitution Disrupts Concerted Cation Dynamics in Formamidinium Hybrid Perovskites

Methylammonium Cation Dynamics in Methylammonium Lead Halide Perovskites: A Solid-State NMR Perspective

A solid-state NMR investigation of the colossal expansion material, Ag3Co(CN)6

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A solid-state NMR investigation of the colossal expansion material, Ag₃Co(CN)₆