Alkyl chain dynamics in perovskite bilayers and their variation with structural phase as studied by powder and single crystal NMR

1996 ◽  
Vol 105 (7) ◽  
pp. 2891-2905 ◽  
Author(s):  
H. Zhang ◽  
N. P. Kulshrestha ◽  
S. E. Woehler ◽  
R. J. Wittebort
Keyword(s):  
Single Crystal ◽  
Alkyl Chain ◽  
Structural Phase ◽  
Chain Dynamics

scholarly journals Phase transition and proton ordering at 50 K in 3-(pyridin-4-yl)pentane-2,4-dione

2017 ◽  
Vol 73 (6) ◽  
pp. 1172-1178 ◽  
Author(s):  
Khai-Nghi Truong ◽  
Carina Merkens ◽  
Martin Meven ◽  
Björn Faßbänder ◽  
Richard Dronskowski ◽  
...  
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Single Crystal ◽  
Structural Phase ◽  
Pyridyl Ring ◽  
Temperature Phase ◽  
Crystallographic Axis ◽  
Temperature Phase Transition ◽  
Intramolecular Hydrogen ◽  
Low Temperature Phase

Single-crystal neutron diffraction experiments at 100 and 2.5 K have been performed to determine the structure of 3-(pyridin-4-yl)pentane-2,4-dione (HacacPy) with respect to its protonation pattern and to monitor a low-temperature phase transition. Solid HacacPy exists as the enol tautomer with a short intramolecular hydrogen bond. At 100 K, its donor···acceptor distance is 2.450 (8) Å and the compound adopts space group C2/c, with the N and para-C atoms of the pyridyl ring and the central C of the acetylacetone substituent on the twofold crystallographic axis. As a consequence of the axial symmetry, the bridging hydrogen is disordered over two symmetrically equivalent positions, and the carbon–oxygen bond distances adopt intermediate values between single and double bonds. Upon cooling, a structural phase transition to the t 2 subgroup P\bar 1 occurs; the resulting twins show an ordered acetylacetone moiety. The phase transition is fully reversible but associated with an appreciable hysteresis in the large single crystal under study: transition to the low-temperature phase requires several hours at 2.5 K and heating to 80 K is required to revert the transformation. No significant hysteresis is observed in a powder sample, in agreement with the second-order nature of the phase transition.

Low temperature frustrated structural phase transition in single crystal La1.85Sr0.15CuO4

1995 ◽  
Vol 197 (5-6) ◽  
pp. 439-443 ◽  
Author(s):  
Z.J. Yang ◽  
M. Yewondwossen ◽  
R.A. Dunlap ◽  
D.J.W. Geldart ◽  
S.L. Yuan ◽  
...  
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Single Crystal ◽  
Structural Phase Transition ◽  
Structural Phase

Dynamic proton disorder and the II–I structural phase transition in (NH4)3H(SO4)2

2009 ◽  
Vol 65 (1) ◽  
pp. 36-44 ◽  
Author(s):  
Yoo Jung Sohn ◽  
Anja Loose ◽  
Michael Merz ◽  
Karine Sparta ◽  
Helmut Klapper ◽  
...  
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Single Crystal ◽  
Powder Diffraction ◽  
Structural Phase ◽  
Local Symmetry ◽  
Crystal Structure Analysis ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Proton Disorder

X-ray powder diffraction, differential scanning calorimetry (DSC)/thermogravimetry (TG) and single-crystal neutron diffraction methods were used to investigate triammonium hydrogen disulfate (NH4)3H(SO4)2 (TAHS) in the temperature range between 293 and 493 K. The temperature-dependent X-ray powder diffraction measurements show a clear hysteresis of the I \leftrightarrow II phase transition of TAHS with transition temperatures of T up = 412.9 (1) K on heating and of T down = 402.6 (1) K on cooling. From the existence of hysteresis and from the jump-like changes of the lattice parameters, the I \leftrightarrow II phase transition of TAHS is considered to be first order. With DSC/TG measurements we confirmed that there is only one phase transition between 293 and 493 K. Through careful investigation on single crystals of TAHS using neutron diffraction, the correct space group (C2/c) of room-temperature TAHS-II phase was confirmed. Crystal structure analysis by single-crystal neutron diffraction showed a strongly elongated displacement ellipsoid of the proton which lies in the middle of the (SO4)H(SO4) dimer with \bar 1 local symmetry. The protons of the NH4 groups also show strongly enlarged anisotropic mean-square displacements. These findings are interpreted in terms of a characteristic proton disorder in the TAHS-II phase.

Sign in / Sign up

Export Citation Format

Share Document