Dielectric relaxation behavior in antiferroelectric metal organic framework [(CH3)2NH2][Fe(III)Fe(II)(HCOO)6] single...

Area of Science:

• Materials Science
• Solid State Physics
• Chemistry

Background:

• Multiferroic metal-organic frameworks (MOFs) exhibit complex electrical properties.
• Understanding relaxation dynamics is key to their application in electronic devices.

Purpose of the Study:

• To investigate the relaxation dynamics of niccolite-type, mixed valence MOF, [(CH3)2NH2][Fe(3+)Fe(2+)(HCOO)6] single crystals.
• To elucidate the relationship between phase transitions and relaxation mechanisms.

Main Methods:

• Dielectric relaxation spectroscopy over a wide frequency range (10⁻²–10⁶ Hz).
• Temperature-dependent measurements from 120 K to 250 K.
• X-ray diffraction analysis.

Main Results:

• Observed an antiferroelectric to paraelectric phase transition near 154 K with relaxor behavior.
• Identified three distinct relaxation processes: bulk conductivity relaxation (explained by small polaron hopping), and two others.
• The fastest relaxation (Ea = 0.17 eV) is attributed to the freezing of dimethylammonium (DMA⁺) cation reorientation.

Conclusions:

• The study provides fundamental insights into relaxation dynamics in niccolite-type MOFs.
• Complete freezing of DMA⁺ cation motion occurs below the phase transition temperature.
• Experimental findings are vital for theoretical models of relaxation in these advanced materials.