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. 2021 Jun 7;14(11):3125.
doi: 10.3390/ma14113125.

Elastic Properties and Energy Loss Related to the Disorder-Order Ferroelectric Transitions in Multiferroic Metal-Organic Frameworks [NH4][Mg(HCOO)3] and [(CH3)2NH2][Mg(HCOO)3]

Zhiying Zhang  1 , Hongliang Yu  1 , Xin Shen  1 , Lei Sun  1 , Shumin Yue  1 , Hao Tang  1
Affiliations

Elastic Properties and Energy Loss Related to the Disorder-Order Ferroelectric Transitions in Multiferroic Metal-Organic Frameworks [NH4][Mg(HCOO)3] and [(CH3)2NH2][Mg(HCOO)3]

Zhiying Zhang et al. Materials (Basel). .

Abstract

Elastic properties are important mechanical properties which are dependent on the structure, and the coupling of ferroelasticity with ferroelectricity and ferromagnetism is vital for the development of multiferroic metal-organic frameworks (MOFs). The elastic properties and energy loss related to the disorder-order ferroelectric transition in [NH4][Mg(HCOO)3] and [(CH3)2NH2][Mg(HCOO)3] were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The DSC curves of [NH4][Mg(HCOO)3] and [(CH3)2NH2][Mg(HCOO)3] exhibited anomalies near 256 K and 264 K, respectively. The DMA results illustrated the minimum in the storage modulus and normalized storage modulus, and the maximum in the loss modulus, normalized loss modulus and loss factor near the ferroelectric transition temperatures of 256 K and 264 K, respectively. Much narrower peaks of loss modulus, normalized loss modulus and loss factor were observed in [(CH3)2NH2][Mg(HCOO)3] with the peak temperature independent of frequency, and the peak height was smaller at a higher frequency, indicating the features of first-order transition. Elastic anomalies and energy loss in [NH4][Mg(HCOO)3] near 256 K are due to the second-order paraelectric to ferroelectric phase transition triggered by the disorder-order transition of the ammonium cations and their displacement within the framework channels, accompanied by the structural phase transition from the non-polar hexagonal P6322 to polar hexagonal P63. Elastic anomalies and energy loss in [(CH3)2NH2][Mg(HCOO)3] near 264 K are due to the first-order paraelectric to ferroelectric phase transitions triggered by the disorder-order transitions of alkylammonium cations located in the framework cavities, accompanied by the structural phase transition from rhombohedral R3¯c to monoclinic Cc. The elastic anomalies in [NH4][Mg(HCOO)3] and [(CH3)2NH2][Mg(HCOO)3] showed strong coupling of ferroelasticity with ferroelectricity.

Keywords: dynamic mechanical analysis (DMA); elastic property; energy loss; ferroelectric transition; metal–organic framework (MOF).

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
OM image of (a) [NH4][Mg(HCOO)3] and (b) [(CH3)2NH2][Mg(HCOO)3] crystals.
Figure 2
Figure 2
SEM image of (a) [NH4][Mg(HCOO)3] and (b) [(CH3)2NH2][Mg(HCOO)3] crystals.
Figure 3
Figure 3
Rietveld fit of XRD patterns of (a) [NH4][Mg(HCOO)3] and (b) [(CH3)2NH2][Mg(HCOO)3] at room temperature.
Figure 4
Figure 4
Structures of (a) [NH4][Mg(HCOO)3] and (b) [(CH3)2NH2][Mg(HCOO)3] at room temperature.
Figure 5
Figure 5
DSC curves of (a) [NH4][Mg(HCOO)3] and (b) [(CH3)2NH2][Mg(HCOO)3] during cooling and heating processes at the rate of 5 K/min.
Figure 6
Figure 6
Temperature dependences of (a) storage modulus E’, (b) loss modulus E’’, (c) loss factor tanδ of [NH4][Mg(HCOO)3] single crystals, (d) normalized storage modulus E’T/E’280, (e) normalized loss modulus E’’T/E’’298 and (f) loss factor tanδ of [NH4][Mg(HCOO)3] pellet determined by DMA during heating at the rate of 2 K/min. The vertical dash-dotted line indicates the ferroelectric transition temperature of 256 K.
Figure 6
Figure 6
Temperature dependences of (a) storage modulus E’, (b) loss modulus E’’, (c) loss factor tanδ of [NH4][Mg(HCOO)3] single crystals, (d) normalized storage modulus E’T/E’280, (e) normalized loss modulus E’’T/E’’298 and (f) loss factor tanδ of [NH4][Mg(HCOO)3] pellet determined by DMA during heating at the rate of 2 K/min. The vertical dash-dotted line indicates the ferroelectric transition temperature of 256 K.
Figure 7
Figure 7
Temperature dependences of (a) storage modulus E’, (b) loss modulus E’’, (c) loss factor tanδ of [(CH3)2NH2][Mg(HCOO)3] single crystals, (d) normalized storage modulus E’T/E’298, (e) normalized loss modulus E’’T/E’’298 and (f) loss factor tanδ of [(CH3)2NH2][Mg(HCOO)3] pellet determined by DMA during heating at the rate of 2 K/min. The vertical dash-dotted line indicates the ferroelectric transition temperature of 264 K.
Figure 8
Figure 8
Double logarithmic plot ln(tanδ) vs. ln(f) for the peak in the temperature dependence of tanδ near 260 K in [NH4][Mg(HCOO)3] (a) and near 270 K in [(CH3)2NH2][Mg(HCOO)3] (b).
See this image and copyright information in PMC

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