Fig. 4: Noncollinear polarity of DBC.
a Top view of Br sublattice along the c-axis. In each layer, Br ions form triangles, and two neighbor layers of Br-triangles twist by 60o. b Schematic diagram of noncollinear orders of LTP and ITP. The Br···[H2Dabco] unit breaks the inversion symmetry, which can be represented by a dipole lying in the ab-plane. Locked by the Br-triangles, the dipoles twist by 60o between the nearest neighbor layers. The difference between LTP and ITP is the twisting sequence, which can be determined by the sign of the next-nearest neighbor interaction (J2). c The alignment of [ClO4] groups in LTP. Here the different layers are distinguished by O’s colors. Along the c-axis, the [ClO4] anions also have the 60o-twist. Along the a-axis, the orientations of [ClO4] anions form the up-up-down-down pattern. d A rough estimation of TC1 of entropy-driven LTP-ITP phase transition. The corresponding state number ΩITP is within the reasonable range.
