Structural phase transition and hydrogen ordering of TlH2PO4 at low temperature

2006 ◽  
Vol 62 (5) ◽  
pp. 719-728 ◽  
Author(s):  
I. H. Oh ◽  
M. Merz ◽  
S. Mattauch ◽  
G. Heger
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Low Temperature ◽  
Structural Phase ◽  
Crystal Structure Analysis ◽  
Temperature Phase ◽  
Structure Model ◽  
Triclinic Space Group ◽  
Space Groups ◽  
Low Temperature Phase

The crystal structure of TlH2PO4 (TDP) has been studied at low temperature. The lattice parameters were derived from high-resolution X-ray powder diffraction in the temperature range between 8 and 300 K. A detailed crystal structure analysis of the antiferroelectric low-temperature phase TDP-III has been performed based on neutron diffraction data measured at 210 K on a twinned crystal consisting of two domain states. The structure model in the triclinic space group P\bar 1 is characterized by a complete ordering of all the H atoms in the asymmetric O—H...O hydrogen bonds. The phase transition from the ferroelastic TDP-II to the antiferroelectric TDP-III phase at 229.5 ± 0.5 K is only slightly of first order and shows no detectable hysteresis effects. Its mechanism is driven by the hydrogen ordering between the partially ordered TDP-II state and the completely ordered TDP-III state. The polymorphism of TDP and the fully deuterated TlD2PO4 (DTDP) is presented in the form of group–subgroup relations between the different space groups.

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 phase transition and crystal structure of CsMgPO4

2015 ◽  
Vol 221 ◽  
pp. 224-229 ◽  
Author(s):  
Maria Orlova ◽  
Sergey Khainakov ◽  
Dmitriy Michailov ◽  
Lukas Perfler ◽  
Christoph Langes ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Low Temperature ◽  
Temperature Phase ◽  
Temperature Phase Transition ◽  
Low Temperature Phase

Structure of N 6-furfurylaminopurine (kinetin) dihydrogenphosphate

2006 ◽  
Vol 62 (1) ◽  
pp. 102-108 ◽  
Author(s):  
G. Ślósarek ◽  
M. Kozak ◽  
J. Gierszewski ◽  
A. Pietraszko
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Low Temperature ◽  
Dynamic Equilibrium ◽  
Temperature Phase ◽  
Polymorphic Phase Transition ◽  
Triclinic System ◽  
Tautomeric Forms ◽  
Network Of Hydrogen Bonds ◽  
Low Temperature Phase

The crystal structure of kinetin dihydrogenphosphate has been determined at 115 and 293 K. Kinetin dihydrogenphosphate undergoes a polymorphic phase transition at 291.1 K. In both phases the crystal belongs to the triclinic system with the symmetry described by the space group P\bar 1. In the low-temperature phase, the unit cell is doubled along the a axis. There is a dynamic equilibrium between different tautomeric forms of the adenine residue, determined by the distribution of H atoms within the network of hydrogen bonds.

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