Structural phase transition in perovskite metal–formate frameworks: a Potts-type model with dipolar interactions

Abstract

We propose a combined experimental and numerical study to describe an order-disorder structural phase transition in perovskite-based [(CH3)2NH2][M(HCOO)3] (M = Zn(2+), Mn(2+), Fe(2+), Co(2+) and Ni(2+)) dense metal-organic frameworks (MOFs). The three-fold degenerate orientation of the molecular (CH3)2NH2(+) (DMA(+)) cation implies a selection of the statistical three-state model of the Potts type. It is constructed on a simple cubic lattice where each lattice point can be occupied by a DMA(+) cation in one of the available states. In our model the main interaction is the nearest-neighbor Potts-type interaction, which effectively accounts for the H-bonding between DMA(+) cations and M(HCOO)3(-) cages. The model is modified by accounting for the dipolar interactions which are evaluated for the real monoclinic lattice using density functional theory. We employ the Monte Carlo method to numerically study the model. The calculations are supplemented with the experimental measurements of electric polarization. The obtained results indicate that the three-state Potts model correctly describes the phase transition order in these MOFs, while dipolar interactions are necessary to obtain better agreement with the experimental polarization. We show that in our model with substantial dipolar interactions the ground state changes from uniform to the layers with alternating polarization directions.

Ferroelectricity in Metal–Organic Frameworks: Characterization and Mechanisms

“…Above the transition temperature, the cation vibration appears as a single broad band as the cation is free to move between three equivalent positions, whereas the vibrations split into multiple sharp lines below the transition temperature . The order–disorder transition was further confirmed by entropy changes during the phase transitions of the crystal structures,, and the ordering can be described by a three‐state 3D Potts model . We further note that order–disorder transitions have been confirmed through the study of deuterated analogues of the MOFs , .…”

Ferroic multipolar order and disorder in cyanoelpasolite molecular perovskites

“…This suggests that the phase transition here is well described in terms of quadrupolar interactions between neighbouring C 3 N 2 By way of context, a three-state Potts model-conceptually similar to the four-state Potts model we use here-was recently employed to describe the phase transition behaviour in the family of multiferroic dimethylammonium-formate MOFs. In that case, it was found that longer-range dipolar interactions were needed to fully explain the experimental data [48]. Our system appears to be simpler (perhaps fortuitously).…”

Raman‐scattering studies of pressure‐induced phase transitions in perovskite‐like acetamidninium manganese formate

“…Dense metal-organic frameworks with short ligands such as HCOO − , N 3 − , CN − , SCN − , and N(CN) 2 − received a lot of interest in recent years due to their magnetic, optical, dielectric, ferroelectric, and multiferroic properties as well as structural phase transitions. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Especially interesting sub-group of these dense metal-organic frameworks are metal formate frameworks templated by protonated amines. Four such compounds were discovered for the first time in 2004, and they were shown to exhibit long-range magnetic order.…”