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Dynamic proton disorder and the II-I structural phase transition in (NH(4))(3)H(SO(4))(2)
Yoo Jung Sohn1, Anja Loose, Michael Merz
1RWTH Aachen University, Institut für Kristallographie, Jägerstrasse 17-19, 52056 Aachen, Germany. sohn@xtal.rwth-aachen.de
Triammonium hydrogen disulfate (TAHS) exhibits a first-order phase transition with hysteresis. Neutron diffraction reveals proton disorder in the TAHS-II phase, impacting its crystal structure.
Area of Science:
- Solid State Chemistry
- Crystallography
- Materials Science
Background:
- Triammonium hydrogen disulfate (TAHS) is a crystalline material with potential applications.
- Understanding its phase transitions and structural properties is crucial for material design.
Purpose of the Study:
- To investigate the phase transition behavior of TAHS between 293 and 493 K.
- To determine the crystal structure of the room-temperature phase (TAHS-II).
- To elucidate the nature of proton disorder in TAHS.
Main Methods:
- X-ray powder diffraction (XRD) for temperature-dependent phase analysis.
- Differential scanning calorimetry (DSC)/thermogravimetry (TG) for thermal event identification.
- Single-crystal neutron diffraction for precise structural determination.
Main Results:
- A first-order phase transition (I <--> II) was observed with significant thermal hysteresis (T(up)=412.9 K, T(down)=402.6 K).
- The space group of the room-temperature TAHS-II phase was confirmed as C2/c.
- Neutron diffraction revealed significant proton disorder within the (SO(4))H(SO(4)) dimers and NH(4) groups in the TAHS-II phase.
Conclusions:
- TAHS undergoes a first-order phase transition characterized by hysteresis.
- The crystal structure of TAHS-II exhibits substantial proton disorder, influencing its properties.
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