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

Area of Science:

• Materials Science
• Condensed Matter Physics
• Crystallography

Background:

• Perovskite-based metal-organic frameworks (MOFs) exhibit complex structural phase transitions.
• The ordering of molecular cations, like dimethylammonium (DMA+), influences these transitions.

Purpose of the Study:

• To investigate the order-disorder structural phase transition in [(CH3)2NH2][M(HCOO)3] MOFs (M = Zn, Mn, Fe, Co, Ni).
• To model the transition using a statistical three-state Potts model, incorporating nearest-neighbor and dipolar interactions.

Main Methods:

• Combined experimental (electric polarization) and numerical (Monte Carlo simulations) approaches.
• Density functional theory (DFT) for evaluating dipolar interactions.
• Application of a modified three-state Potts model on a cubic lattice.

Main Results:

• The three-state Potts model accurately describes the phase transition order in the studied MOFs.
• Dipolar interactions are crucial for achieving quantitative agreement with experimental electric polarization.
• The model predicts a ground state transition from uniform to alternating polarization layers with increasing dipolar interactions.

Conclusions:

• The three-state Potts model, enhanced with dipolar interactions, provides a robust framework for understanding phase transitions in these perovskite-based MOFs.
• The interplay between cation ordering and dipolar forces dictates the material's polarization behavior.