²H NMR studies of the antiferrodistortive phase transition in betaine phosphite and betaine phosphate

Abstract

Single crystals of betainc phosphitc and bctainc phosphate were investigated in the antiferrodistortive and paraelastic phases. The comparison of the data obtained in these phases indicates an order-disorder type of phase transition. It could be shown that the t,wo betaine molecules, which can be distinguished by 'H NMR, are located in the high-temperature phase in the mirror plane only in a statistical serise arid tilt by about *7.8" in opposite direction out of this mirror plane below the phase transition.Betainphosphit-und Betairiphosphateinkristalle wurden rnit Hilfe der 'H-NMR in der antiferrodistortiveri und der paraelastischen Phase untersucht. Ein Vergleich der IlleBergebnisse in diesen Phasen lassen auf eiri Ordriurigs-Unordnungs-Verhalten am Phasenubcrgang schliefien. Die Betairiphosphat-und Betairiphosphitmolekiile besetzeri die scheinbar rntstandene Spiegelebene nur irn Zeitmittel. Die Verkippung der Betairirriolekule in Bezug auf die Spicgclcbcnc bctragt beim Uhergang in die antiferrodistortive Phase ungefahr *7.8" in entgegengcsctzter Richtung.') Linnkstr. 5 ,

2H nuclear magnetic resonance studies on the deuteron dynamics in betaine phosphate/phosphite mixed crystals

“…The patterns for the rotations around the crystallographic a-and c-directions (not shown here) could also be analysed by using this relationship to pure DBP and DBPI. From this correspondence of 2 for all three rotations, it follows immediately that the respective deuterium lattice sites have, within the experimental error, the same EFG tensors as the sites in pure DBP and DBPI [10]. This finding is not surprising if one assumes the EFG tensor to be a local quantity, i.e.…”

“…To answer the question of whether the rotation patterns of DBP 0.3 DBPI 0.7 are similar to those of DBP and DBPI or whether 'mixed' lines occur, it was inevitable that we made use of the knowledge that we have on pure DBP and DBPI [9,10]. Therefore the overlay of the rotation patterns of the two pure substances is added in figure 3, where the fits of the respective rotations are displayed as full (DBP) and dashed (DBPI) curves.…”

“…The investigation of symmetry and structural changes in relation to the phase transitions by x-ray, dielectric and magnetic resonance techniques revealed details of the static and dynamic properties of the protons in the hydrogen bonds [4][5][6][7][8]. By means of 2 H nuclear magnetic resonance (NMR) spectroscopy carried out on the deuterated compounds DBP and DBPI [9][10][11], the high-temperature phase transition was characterized as of orderdisorder type, and the chemical exchange processes were quantitatively analysed by means of two-dimensional 2 H NMR exchange spectroscopy.…”

Phase diagram of the betaine arsenate–betaine phosphate mixed-crystal system by dielectric hysteresis and current curves

“…15,17 This is especially true in the case of BPI and the BP: BPI͑x͒ system. 30,31 The distortion of the tetrahedra 32,33 was shown to contribute to the polarization, and this was also proposed as a mechanism responsible for the ordered phase, where only partial proton order was found. Raman results 5 support the importance of the tetrahedra dynamics in the various phases, both with temperature and with concentration.…”

Dielectric Properties of Betaine Phosphite-Betaine Phosphate in Improper Ferroelastic Phase

“…Both crystals with temperature decrease obey the same symmetry change P2 1 /m(Z = 2) → P2 1 /c(Z = 4) [2][3][4][5] at improper ferroelastic phase transition temperature T c1 = 355 K in BPI [6] and T c1 = 365 K in BP [7]. Then BPI transforms into ferroelectric state at T c2 = 196-225 K [6,8], but in BP antiferroelectric phases are identified with phase transition temperatures T c2 = 86 K and T c3 = 81 K [7].…”