Incommensurately modulated structure of morpholinium tetrafluoroborate and configurational versus chemical entropies at the incommensurate and lock-in phase transitions

0479715 - FZÚ 2018 RIV GB eng J - Článek v odborném periodiku
Noohinejad, L. - van Smaalen, S. - Petříček, Václav - Schönleber, A.
Incommensurately modulated structure of morpholinium tetrafluoroborate and configurational versus chemical entropies at the incommensurate and lock-in phase transitions.
Acta Crystallographica Section B-Structural Science Crystal Engineering and Materials. Roč. 73, Jun (2017), s. 836-843. E-ISSN 2052-5206
Grant CEP: GA ČR(CZ) GA15-12653S
Institucionální podpora: RVO:68378271
Klíčová slova: incommensurately modulated structure * morpholinium tetrafluoroborate * configurational entropy
Obor OECD: Condensed matter physics (including formerly solid state physics, supercond.)
Impakt faktor: 6.467, rok: 2017

Morpholinium tetrafluoroborate belongs to a class of ferroelectric compounds ABX4. However, it does not develop ferroelectric properties because the incommensurate phase below Tc,I = 153 K is centrosymmetric, the threefold superstructure below Tc,II = 117–118 K possesses the acentric but non-ferroelectric space group P212121. A structure model for the incommensurately modulated phase is reported. A mechanism is proposed for the phase transitions, whereby at low temperatures morpholinium cations are shaped around the tetrafluoroborate anion in order to optimize the interactions with one orientation of this anion and, thus, forcing [BF4] anions into this orientation.
Trvalý link: http://hdl.handle.net/11104/0275716