Molecular Motions and Phase Transitions in Solid CH3NH3PbX3 (X = C1, Br, I) as Studied by NMR and NQR

1991 ◽  
Vol 46 (3) ◽  
pp. 240-246 ◽  
Author(s):  
Qiang Xu ◽  
Taro Eguchi ◽  
Hirokazu Nakayama ◽  
Nobuo Nakamura ◽  
Michihiko Kishita
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Molecular Motions ◽  
Isotropic Reorientation ◽  
Higher Temperature ◽  
Successive Phase

AbstractThe temperature dependence of 35C1, 81Br, and 127I NQR frequencies and 1Hspin-lattice relaxation times (T1) for CH3NH3PbX3 (X = Cl, Br, I) was measured through the successive phase transitions in these solids. The isotropic reorientation of the CH3NH3 ions takes place in the higher-temperature phases (tetragonal [I4/mcm] and cubic) of the three salts (Ea= 11 kJ mol -1). T1's in the lowest-temperature phases (orthorhombic) indicate that the cations undergo correlated C3-reorientation in the chloride (Ea = 5.45 kJ mol -1)and in the iodide (Ea = 5.80 kJ mol -1, whereas correlated (Ea = 2.40 kJ mol-1) and uncorrected (Ea = 7.50 kJ mol-1) C3- reorientations are excited in the bromide. It is also revealed that the rotational tunneling of the cations governs T1 at lowtemperature region in the orthorhombic phases of these salts

Structure and Successive Phase Transitions of RGeBr3 (R = Alkylammonium) Studied by Means of NQR

1996 ◽  
Vol 51 (5-6) ◽  
pp. 686-692 ◽  
Author(s):  
Shusaku Gotou ◽  
Tsutomu Okuda ◽  
Toshirou Takahashi ◽  
Hiromitsu Terao ◽  
Koji Yamada
Keyword(s):  
Phase Transitions ◽  
Crystal Structures ◽  
Conduction Mechanism ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Rietveld Analysis ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Spin Lattice ◽  
Successive Phase

Abstract A series of tribromogermanate(II) complexes RGeBr3 (R = CH3NH3, (CH3)2NH2, (CH3)4N, C2H5NH3, (C2H5)4N) have been synthesized and characterized by 81Br NQR, AC conductivity, DTA, and X-rax diffraction. These measurements revealed the presence of successive phase transitions in these complexes. The crystal structures of Phases I and II in (NH3)4NGeBr3 were derived from the Rietveld analysis of powder X-ray diffraction. The electric conductivity was considerably high in CH3NH3GeBr3 and (NH3)4NGeBr3. The conduction mechanism is discussed on the basis of 81Br NQR spin-lattice relaxation times and crystal structures.

Successive Phase Transitions in Potassium Hexachloroselenate(IV) Revealed by 35Cl NQR

1996 ◽  
Vol 51 (5-6) ◽  
pp. 705-709 ◽  
Author(s):  
Tetsuo Asaji ◽  
Masaki Ohkawa ◽  
Takehiko Chiba ◽  
Makoto Kaga
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Structural Phase Transitions ◽  
Spin Lattice ◽  
35Cl Nqr ◽  
Successive Phase

Abstract K2SeCl6 undergoes structural phase transitions of first order at 35 K, 65 K, and 79 K. The temperature dependence of the 35Cl NQR spin-lattice relaxation time suggests that the phase transitions at 65 K and 79 K are displacive ones associated with a resonant soft mode. The presence of a precursor cluster is suggested by the temperature dependence of the signal intensity above 79 K.

Bonded Hydrogen and Trapped H2 in a-Si1−xGex:H Alloys

1989 ◽  
Vol 149 ◽  
Author(s):  
E. J. Vanderheiden ◽  
G. A. Williams ◽  
P. C. Taylor ◽  
F. Finger ◽  
W. Fuhs
Keyword(s):  
Temperature Dependence ◽  
Molecular Hydrogen ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
H Nmr ◽  
Local Environments

ABSTRACT1H NMR has been employed to study the local environments of bonded hydrogen and trapped molecular hydrogen (H2) in a series of a-Si1−xGex:H alloys. There is a monotonic decrease of bonded hydrogen with increasing x from ≈ 10 at. % at x = 0 (a-Si:H) to ≈ 1 at. % at x = 1 (a-Ge:H). The amplitude of the broad 1H NMR line, which is attributed to clustered bonded hydrogen, decreases continuously across the system. The amplitude of the narrow 1H NMR line, which is attributed to bonded hydrogen essentially randomly distributed in the films, decreases as x increases from 0 to ≈ 0.2. From x = 0.2 to x ≈ 0.6 the amplitude of the narrow 1H NMR line is essentially constant, and for x ≥ 0.6 the amplitude decreases once again. The existence of trapped H2 molecules is inferred indirectly by their influence on the temperature dependence of the spin-lattice relaxation times, T1. Through T1, measurements it is determined that the trapped H2 concentration drops precipitously between x = 0.1 and x = 0.2, but is fairly constant for 0.2 ≤ x ≤ 0.6. For a-Si:H (x = 0) the H2 concentration is ≈ 0.1 at. %, while for x ≥ 0.2 the concentration of H2 is ≤ 0.02 at. %.

Studies of Successive Phase Transitions and Molecular Motions in [Mg(H2O)6][SiF6] by 1,2H and 19F NMR

1998 ◽  
Vol 53 (6-7) ◽  
pp. 453-458 ◽  
Author(s):  
Junko Kimura ◽  
Takeshi Fukase ◽  
Motohiro Mizuno ◽  
Masahiko Suhara
Keyword(s):  
Phase Transitions ◽  
Nmr Spectra ◽  
Quadrupole Coupling Constant ◽  
Coupling Constant ◽  
Molecular Motions ◽  
Exponential Factor ◽  
H Nmr ◽  
Quadrupole Coupling ◽  
Constant E ◽  
Successive Phase

Abstract The successive phase transitions of [Mg(H2O)6][SiF6] were studied by measuring 2H NMR spectra. The quadrupole coupling constant e2Qq/h and asymmetry parameter η changed drastically at each transition temperature. 1,2H and 19F NMR Tl were measured for this compound to study the relation between the molecular motions and the successive phase transitions. The activation energy Ea and the pre-exponential factor τ0 for the reorientation of [SiF6]2- were estimated as 28 kJmol-1 and 6.0 x 10-14 s, and those of the 180° flip of H2O as 33 kJmol-1 and 4.0x 10-14 s. These two motions occur rapidly even in phase V. For the reorientation of [Mg(H2O)6]2+ , Ea = 62 kJmol-1 and τ0 = 1.1 x 10-16 s were obtained from the simulation of 2H NMR spectra. The jump rate of this motion is of the order of 104 -106 s-1 in phase II. These results suggest that the successive phase transitions are closely related to the motion of [Mg(H2O)6]2+ .

NQR and Phase Transitions of Tetramethylammonium Tetrahalogenomercurates (II)

1996 ◽  
Vol 51 (5-6) ◽  
pp. 755-760 ◽  
Author(s):  
Hiromitsu Terao ◽  
Tsutomu Okuda ◽  
Koji Yamada ◽  
Hideta Ishihara ◽  
Alarich Weiss
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Reorientational Motion ◽  
Spin Lattice ◽  
Increasing Temperature

NQR and DTA revealed phase transitions in [(CH3)4N] 2HgBr4 and [(CH3)4N] 2HgI4 at 272 K and 264 K, respectively. The NQR resonance lines faded out with increasing temperature. From preliminary measurements of 81Br NQR spin-lattice relaxation times and 199Hg NMR a reorientational motion of HgBr4 ions around one of their pseudo C3 axes in the room temperature phase of [(CH3)4N] 2HgBr4 is suggested.

Interrelation Between Molecular Motions and Structure in Solid Trimethylamine-boron-trichloride as Studied by NMR

1992 ◽  
Vol 47 (11) ◽  
pp. 1157-1160
Author(s):  
S. Głowinkowski ◽  
, S. Jurga ◽  
E. Szcześniak
Keyword(s):  
Molecular Structure ◽  
Relaxation Times ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Molecular Motions ◽  
Boron Trichloride ◽  
Second Moment ◽  
Spin Lattice ◽  
Temperature Dependences

AbstractThe temperature dependences of proton second-moment and spin-lattice relaxation times (T1 and T1ρ) have been measured in solid (CH3)3NBCl3. The nature of reorientation processes occurring in the complex has been established and the activation parameters determined. The motions are discussed in relation to the molecular structure of the complex

scholarly journals Role of NH4 ions in successive phase transitions of perovskite type (NH4)2ZnX4 (X = Cl, Br) by 1H MAS NMR and 14N NMR

RSC Advances ◽  
2018 ◽  
Vol 8 (21) ◽  
pp. 11316-11323 ◽  
Author(s):  
Ae Ran Lim
Keyword(s):  
Phase Transitions ◽  
Chemical Shifts ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
1H Mas Nmr ◽  
Spin Lattice ◽  
Successive Phase ◽  
Perovskite Type

The 1H chemical shifts and the spin-lattice relaxation time, T1ρ, in the rotating frame of (NH4)2ZnX4 (X = Cl, Br) are observed in order to investigate local phenomena related to successive phase transitions.

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