Effect of bromine deficiency on the lattice dynamics and dielectric properties of alpha-phase diisopropylammonium bromide molecular crystals

Article abstract of DOI:10.1016/j.jpcs.2017.10.004

Diisopropylammonium bromide (DIPAB) molecular ferroelectric crystals were synthesized and examined to exhibit a large electric polarization (～23μC/cm²), a large dielectric constant in the α-phase. Although the PXRD pattern indicates that the α-DIPAB sample has an overall excellent crystallinity, our analysis of its FT-IR and Raman vibrational spectra suggests the presence of disorder in the synthesized crystals as indicated by the presence of broad features in the Raman spectrum. Using vdW+DF2 calculations, we identified the majority of vibrational modes in the experimental spectra and analyzed the ones due to Br-disorder. We found that the bromine (Br) deficiency strongly affects the electric properties of α-DIPAB. Particularly, the experimentally measured dielectric constant of α-DIPAB is large (～20), whereas the DFT-based calculations of the ideal DIPAB give much smaller values (～2-3). We find that Br-deficiency is responsible for large dielectric constant of the DIPAB crystal with calculated value of ～15-20. Furthermore, we showed that the van der Waals forces have a slight effect on the structural parameters, only causing a small shift in the vibrational frequencies. The main vibrational features of the DIPAB crystal in the Raman spectrum were shown to be driven by covalent bonding in the DIPA molecules and hydrogen bonds between the molecules with Br.

Full text of DOI:10.1016/j.jpcs.2017.10.004

Accepted Manuscript
Effect of bromine deficiency on the lattice dynamics and dielectric properties of alpha-
phase diisopropylammonium bromide molecular crystals
Ahmad Alsaad, Chris M. Marin, Nabil Alaqtash, Hsien-Wen Chao, Tsun-Hsu Chang,
Chin Li Cheung, A. Ahmad, I.A. Qattan, Renat F. Sabirianov
PII:
S0022-3697(17)31141-1
10.1016/j.jpcs.2017.10.004
PCS 8234
DOI:
Reference:
To appear in: Journal of Physics and Chemistry of Solids
Received Date: 22 June 2017
Revised Date: 29 September 2017
Accepted Date: 2 October 2017
Please cite this article as: A. Alsaad, C.M. Marin, N. Alaqtash, H.-W. Chao, T.-H. Chang, C.L. Cheung,
A. Ahmad, I.A. Qattan, R.F. Sabirianov, Effect of bromine deficiency on the lattice dynamics and
dielectric properties of alpha-phase diisopropylammonium bromide molecular crystals, Journal of
Physics and Chemistry of Solids (2017), doi: 10.1016/j.jpcs.2017.10.004.
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ACCEPTED MANUSCRIPT
Effect of Bromine Deficiency on the Lattice Dynamics and Dielectric Properties of
Alpha-Phase Diisopropylammonium Bromide Molecular Crystals
1
2
3
4
4
Ahmad Alsaad, Chris M. Marin, NabilAlaqtash, Hsien-Wen Chao, Tsun-Hsu Chang, Chin Li
2
1
6
5
Cheung, A. Ahmad, I.A. Qattan, and Renat F. Sabirianov
1
Department of Physical Sciences, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110,
Jordan
2
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588, United States
3
Department of Physics, The Hashemite University, P.O. Box 330127, Zarqa 13133, Jordan
4
Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan
5
Department of Physics, University of Nebraska at Omaha, Omaha, NE 68182, United States
6
Department of Applied Mathematics and Sciences, Khalifa University of
Science, Technology and Research, P.O. Box 127788, Abu Dhabi, UAE.
Keywords: Bromine Deficiency; Lattice Dynamics; Dielectric Properties; Alpha-Phase Diisopropylammonium
Bromide; FT-IR and Raman vibrational spectra
Diisopropylammonium bromide (DIPAB) molecular ferroelectric crystals were synthesized
2
and examined to exhibit a large electric polarization (~23ꢀC/cm ), a large dielectric constant in
the α-phase. Although the PXRD pattern indicates that the α-DIPAB sample has an overall
excellent crystallinity, our analysis of its FT-IR and Raman vibrational spectra suggests the
presence of disorder in the synthesized crystals as indicated by the presence of broad features in
the Raman spectrum. Using vdW+DF2 calculations, we identified the majority of vibrational
modes in the experimental spectra and analyzed the ones due to Br-disorder. We found that the
bromine (Br) deficiency strongly affects the electric properties of α-DIPAB. Particularly, the
experimentally measured dielectric constant of α-DIPAB is large (~20), whereas the DFT-based
calculations of the ideal DIPAB give much smaller values (~2-3). We find that Br-deficiency is
responsible for large dielectric constant of the DIPAB crystal with calculated value of~15-20.
Furthermore, we showed that the van der Waals forces have a slight effect on the structural
parameters, only causing a small shift in the vibrational frequencies. The main vibrational
features of the DIPAB crystal in the Raman spectrum were shown to be driven by covalent
bonding in the DIPA molecules and hydrogen bonds between the molecules with Br.
1
. Introduction
Ferroelectric materials are promising candidates for applications in piezoelectric,
pyroelectric, optoelectronic and nonlinear devices. Particularly, organic ferroelectric materials
are highly desirable due to their environmentally friendly (lead-free) compositions, light weight,
1
,2
and mechanical flexibility. They have shown promises for a wide range of applications
3
4
5
including memory chip, sensing, actuation, energy harvesting, and fast switchable data
1

ACCEPTED MANUSCRIPT
6
storage. One distinct advantage of organic ferroelectrics is that they can be directly printed, as
7
demonstrated in an all-printed ferroelectric active matrix sensor network using P(VDF-TrFE).
Recent research effort to design molecular crystals with conventional electronic functions has
garnered immense interest because of the flexibility in designing the molecular components and
assembling them in ordered manners with close to atomic precision.
Applications of organic ferroelectrics have been restricted due to their limitations such as a
low spontaneous polarization, low melting temperature, low Curie temperature (T ), small
c
dielectric constant and a weak piezoelectricity. Recently discovered organic molecular crystals
have an aptitude to overcome these weaknesses. For example, diisopropylammonium chloride
2
(
4
2
DIPAC) exhibits a ferroelectric phase with a spontaneous polarization of 8.2 ꢀC/cm and T of
c
8
40 K. Furthermore, diisopropylammonium bromide (DIPAB) has spontaneous polarization of
3 ꢀC/cm , which is close to that of barium titanate (BTO), and high T of 426 K above that of
2
c
9
,10,11
BTO, large dielectric constant, and a low dielectric loss.
response and well-defined ferroelectric domains.
DIPAB exhibits good piezoelectric
9
These attractive ferroelectric and piezoelectric properties of DIPAB and DIPAC molecular
crystals make them targets of intensive research. They can potentially be used for data storage,
1
2
13,14
energy harvesting, nonlinear electro-optic phenomena in frequency mixing devices,
2
ferroelectric sensors and promising for flexible electronics. Applications of these ordered
molecular systems as nanoscale electronics components require a precise control of their
nucleation, growth in size and phases, orientation and locations. Recently surfaced arrangements
of ferroelectric microcrystals of (DIPAB) were grown from solution at room temperature on
silicon substrates and examined by means of x-ray diffraction(XRD), atomic force
1
5
microscopy(AFM), electron microscopy, and piezo-response force microscopy. Several issues
such as polarization ordering, optimizing dielectric and structural properties and switching lattice
dynamics are critical issues in the physics of ferroelectrics, which should be undertaken before
1
6
taking into account any practical applications.
For some ferroelectric molecular crystals, post heat treatments after crystal formation up to
several hundred degrees Celsius are necessary to “activate” the crystals in correct phases to
exhibit a ferroelectric behavior. These difficulties post great challenges in pursuing the
applications of molecular crystals for real world high-density electronics.
Since molecular crystals of DIPAB have a strong potential to be a lead-free alternative to
lead zirconium titanate in ferroelectric memory, several studies have been reported to address the
structure-property relationship in DIPAB crystal. However, the nature of crystal bonding and
atomic structures, the origin of large dielectric constant and low tangent loss have not yet
resolved in detail. The vibrational spectroscopy of molecular materials, especially Fourier-
transformed infrared (FT-IR) and Raman spectroscopy, is well suited to study these properties of
DIPAB because it is very sensitive to the disorder, particle size, mechanical and electronic
properties. Properties of DIPAB and molecular crystals in general depend strongly on the degree
of their crystalline order. For DIPAB, the disorder in the positions of bromine (Br) atom in the
crystal may strongly affect its mechanical and electric properties because Br-H hydrogen bonds
are critical in forming the strong bonding between organic molecules in these classes of
molecular crystals. Recently, Raman, IR spectroscopic measurements and computational studies
have been performed to identify the vibrational frequencies of orthorhombic and monoclinic
1
7
phases of DIPAB at room temperature.
2

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In this study, we investigated the vibrational spectra of α-phase DIPAB molecular crystals
using both FT-IR and Raman spectroscopic techniques and correlated the data of the
corresponding dielectric measurement and theoretical predictions for ideal and bromine-deficient
crystals. Powder X-ray diffraction (PXRD) measurements and calculations of equilibrium lattice
parameters and spontaneous polarization of ꢀ-DIPAB were performed to elucidate the lattice
structures and lattice dynamics. Using the DFT-based method, we identified the vibrational
frequencies associated with the chemical bonds connected to bromine (Br) atoms in the DIPAB
crystals. Strikingly, though α-phase DIPAB polycrystalline samples were measured to have a
large dielectric constant, ~17, at 2.4GHz, the calculated static dielectric constant of the ideal
DIPAB crystal is low (~2-3). We showed that the calculated vibrational spectra could help to
identify the presence of disorder in synthesized crystals and the associated modifications of
vibrational modes. We predicted that a Br vacancy substantially affect the intermolecular
bonding within the crystal and its vibrational spectra. The Br-deficiency resulted in a drastic
increase of the calculated dielectric constant (~15-20). Using vdW+DF2 method, the van der
Waals forces was shown to have a slight effect on the structural parameters and cause a small
shift in the vibrational frequencies, while the main features of the DIPAB crystal were driven by
covalent bonding inside the DIPA molecules and hydrogen bonds of the molecules with Br.
2
. Experimental and Computation Methods
Synthesis of α-phase diisopropylammonium bromide
α-phase diisopropylammonium bromide (α-DIPAB) was synthesized by the direct reaction of
diisopropylamine (99.5% DIPA, Acros Organics) with hydrobromic acid (47-49% HBr, Fisher).
Both reagents were used without further purification. Briefly, in a typical reaction, 4 mL of HBr
was rapidly added to 5 mL of DIPA in an open beaker chilled in an ice bath. Upon addition,
white precipitate immediately formed. Once the mixture cooled down, 70 mL of dry methanol
(
˚
99.9%, Fluka) was used to re-dissolve the white powder with vigorous stirring and heating to 30
C. The methanol solution was placed in a freezer to recrystallize the product overnight. The
obtained long, needle-like crystals were then separated from the solution and dried in a
convection oven at 50 °C for 1.5 h. Finally, to produce pure α-DIPAB products, 0.5 g of the
white crystals were annealed in a commercial microwave oven operated at 700 W for 15 s,
resulting in a fine white powder.
Characterization of α-DIPAB samples
The crystal structure of the α-DIPAB sample was assessed using powder X-ray diffraction
(PXRD). The Cu Kα source of the diffractometer (PANalytical Empyrean) has an average
wavelength of 1.544 Å. The FT-IR spectrum of the sample was obtained using a Thermo Nicolet
Avatar 380 FT-IR with a Smart Performer ATR accessory and a zinc selenide crystal. The
Raman spectroscopy was performed using a DXR Raman microscope (Thermo Scientific) with a
5
32 nm laser. The dielectric property and loss tangent measurements of pelleted α-DIPAB
samples were performed using a home-made resonant cavity at 2.45 GHz.
3

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Theoretical modeling of α-DIPAB molecular crystals
1
8,19
First-principles density functional theory
simulations were used to model ideal and Br-
deficient DIPAB crystal structures. Their electronic structures were calculated using the
2
0
projector augmented wave (PAW) method as implemented in the VASP. The Perdew-Burke-
2
1
Ernzerhof (PBE) functional for the exchange-correlation functional the cut-off energy is 400
eV and a 4 x 4 x 4 Monkhorst-pack grid. The atomic positions were relaxed with the Hellmann-
Feynman forces <0.003 eV/Å. We applied a version of the van der Waals density functional
2
2
(
vdW-DF2) by Dion et al, which employed a more accurate semi-local exchange functional
2
3,24
and the use of a large-N asymptote gradient correction in determining the vdW kernel.
This
method was shown to produce a reliable equilibrium spacing between non-covalently bound
complexes, as well as in binding energy, especially when hydrogen bonding plays a major role in
molecular crystal formation compared to vdW interactions.
3
. Results and Discussions
8
Fu et.al. reported that in an experimentally grown crystalline sample of DIPAB, two different
polymorphs could be formed: one is the ferroelectric phase labeled P2 (referred as the α-phase)
1
at room temperature and the other is the paraelectric structure labeled P21/m (referred as the β-
phase) at high temperature. Structure characterization by PXRD (data shown in Fig. 1 in
Ref.[25])) revealed that the ferroelectric phase belongs to the monoclinic crystal system at room
9
temperature, with a polar point group C
2
and a chiral space group P2
1
shown schematically in
(
Fig. 1 (a)). In contrast, at high temperature, DIPAB adopts themonoclinic crystal structure with
2 1
a nonpolar point group D and a chiral space group P2 referred to as P21/m and illustrated
schematically in (Fig. 1(b)), which is ferroelectrically inactive.
As-prepared samples of DIPAB show good crystallinity as examined by PXRD. We do not
observe any diffraction peaks corresponding to the presence of β-phase of DIPAB. There are
small shoulders at the (001) and (101) peaks that may indicate some disorder (See Fig. 1 in Ref.
[
25]). We employed XRD-derived structural parameters as the initial structure in our ab initio
2
6,27
calculations. The optimized lattice parameters are in good agreement with the reported data
o
(a = 7.946 Å, b = 8.1567 Å, c = 7.974 Å, and β = 116.511 in α-phase and very similar in β-
phase (See table. 1 in Ref. [25]).
4

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1
Fig.1. Schematic view of the molecular structure of (a) P2 (α) polar ferroelectric phase and (b)
P21/m (β) paraelectric centrosymmetric phase. The green arrows indicate the direction of the local
dipoles. Absorbance of FT-IR and intensities of Raman vibrational spectra (a.u.) of (c) an ideal
α-DIPAB crystalline structure and (d) an α-DIPAB crystalline structure with Br-deficiency
obtained using DFT (including vdW interactions) compared to experimental data. Excerpts e and
-1
f show details of Raman spectra in the window of 150-350 cm .
The structure of DIPAB can be regarded as layered where the layers of DIPA molecules are
bonded through the layer of bromide ions. The molecules in P2 α-phase illustrated in Fig. 1(a)
1
has arranged to have C-N-C bonds aligned to produce a large electric polarization of 22.64
2
μC/cm . However, spontaneous polarization of the centrosymmetric monoclinic P21 β-phase
/m
was found to be exactly zero as shown schematically in Fig. 1(b).
DFT calculations suggest that the emergence of the spontaneous polarization in DIPAB is
driven by a cooperative atomic distortion that breaks the mirror symmetry plane of each single
9
molecule, resulting in an asymmetric arrangement off the charges. The Br-mediated hydrogen
bond is strong and stabilizes α-phase. The phase transition from ferroelectric α-phase to
paraelectric β-phase occurs at 426 K, well above room temperature, therefore, making DIPAB
technologically attractive for device applications.
The analysis of chemical bonding and non-specific van der Waals interactions is critical for
designing electronic devices from molecular systems. In order to elucidate the role of the
interactions between molecules mediated by bromide ions, we performed experimental
measurements of DIPAB using FT-IR and Raman spectroscopy, as well as a theoretical DFT
analysis of the vibrational spectra. Fig. 1(c) shows the FT-IR and Raman spectra compared to the
calculated vibrational spectra of ideal DIPAB. DFT analysis show that majority of the peaks
correspond to the vibrational modes of the ideal DIPAB in P2 α-phase. Arrows indicate peaks
1
that correspond to the vibrational modes of Br-DIPA hydrogen bonds. The noticeable differences
-1
-1
of experimental spectra are the features (broad peaks) around 180 cm and 250 cm as
5

ACCEPTED MANUSCRIPT
highlighted in the enlarged excerpt in Fig.1(e). These are not present in the calculated spectra of
ideal DIPAB and potentially arise due to Br disorder.
In order to analyze the effect of Br deficiency, we performed analysis of DIPA crystals in the
same phase, i.e. Br is vacated from the crystal. Fig. 1(d) shows that modes related to Br hydrogen
-1
bonding to DIPA disappear in the spectra. Specifically, vibration modes at 212 cm are not
-1
-1
present in the vibrational spectra, as well as modes at 505 cm and 1600 cm . The former
corresponds to rotation/twisting of DIPA molecule, while the latter are due to transversal
movement of hydrogen atom with respect to N-H-Br bond. While modes related to Br disappear,
-1
-1
a few new vibrational modes appear with wavenumbers near 180 cm and 250 cm (highlighted
in excerpt of Fig. 1(f). These modes correspond to two broad peaks in Raman spectra measured
in our samples. Thus, we can conclude that some degree of Br disorder is present in our
experimental samples.
The comparative analysis of DFT-based calculations shows that Br-deficiency causes
significant changes to the electronic properties of DIPAB. The origin of the stability of DIPAB
ferroelectric properties lies in the strong bonding between DIPA molecules mediated by Br. The
Br-DIPA binding energy calculated per unit cell as
ꢁE (= E(DIPAB) - E(DIPA) - 2E(Br)) is
-10.93 eV. This value is large. Assuming that Br forms several hydrogen bonds with its
neighboring DIPA molecules (4 nearest neighbors at ~2.4 Å and 12 next nearest hydrogen
neighbors at ~3.3 Å per unit cell), each bond strength is ~0.6-0.9 eV. This value is an order of
magnitude smaller than the typical strength of a covalent bond (~10 eV), but is substantially
larger than typical value of the van der Waals driven bonds (~0.05 eV). The strength in
intermolecular bonding makes this material considerably harder than the molecular solids bound
by vdW interactions alone. The latter are usually softer and have lower decomposition or melting
temperature. In contrast, DIPAB is stable and shows ferroelectric properties up to 426 K.
We examined the effect of vdW forces on the electronic and vibrational properties of DIPAB
by comparing the traditional DFT calculations and using vdW+DF2 method. We found that
inclusion of vdW correction to energy results in a small increase of the equilibrium lattice
parameters (around 2% more than the one calculated using GGA). The small value of the
difference reflects the weakness of vdW interactions comparing to electrostatic interactions
mediated by Br that are already taken into account in DFT. The increase in the equilibrium
volume (by ~6%) when vdW interaction included is due to the enhancement of repulsive
2
3
interactions in vdW+DF2 method.
Additionally, vdW interactions cause a small shift in the calculated vibrational frequencies.
As can be seen in Fig.1(c-f), the main features of the experimental Raman spectrum for the
DIPAB sample are well reproduced using DFT. The vibration modes frequencies are determined
mainly by the covalent bonding between atoms of DIPA molecules and hydrogen bonds of the
molecules with Br. Modes specifically related to Br bonding with DIPA are at the wavenumbers
-1
of 213, 382, 515, 845 and 1615 cm , as indicated by the arrows in Fig.1(c). These modes are
-1
shifted by about 2.5% (or ~40 cm ). These modes are not present in calculated spectra if Br is
removed from the system as can be seen in Fig. 1(d). However, several low-energy modes (181-
-1
2
88 cm ) related to the rotation and twisting of DIPA molecules appear in in calculated spectra
(excerpt in Fig. 1(f) and were observed in the experimental data.
The modification of the bonding with the Br-deficiency displays itself most drastically when
examine its effect on the dielectric constant of DIPAB. The calculated static dielectric constant is
6

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9
,14
only 2.3. This drastically contrasts the large value of the measured dielectric constant.
The
electronic contribution to the dielectric constant is 1.54. Our measurements show a much larger
value of the dielectric constant. The -DIPAB sample has a measured dielectric constant of 17.4
0.25 and tangent loss of 0.00068~0.0008 at room temperature. The calculations of static
dielectric constant for the Br-deficient crystals show much larger values of =18. This value is
much closer to the experimentally measured . The obvious reason can be inferred from the
α
±
ε
ε
appearance of a large number of low-energy excitation modes in the absence of strong Br-DIPA
hydrogen bond that alters the molecular dipole alignment in the crystal. For example,
-1
-1
eigenvectors of the vibrational modes at 182.95 cm and 181.41 cm correspond to
twisting/rotation of the molecules as shown in Fig.2 (See Ref. [25]). The changes in C-N-C angle
and related shift of hydrogen atoms in this mode change the polarization of the molecules.
Conclusions
Synthesized ferroelectric low temperature P2 (α)-phase of DIPAB molecular crystals exhibit
1
2
a large electric polarization at room temperature (~23
ꢀ
C/cm ) and a large dielectric constant.
While PXRD spectra suggest overall excellent crystallinity, the vibrational spectra, investigated
by FT-IR and Raman spectroscopy, indicate the presence of Br disorder. Our DFT-based
calculations show that Br vacancies substantially change the strength and nature of crystal
bonding, as well as vibrational spectra and dielectric constant of the material. Although
calculated vibrational spectra of the ideal
α-DIPAB agree with experimental data very well
overall, Br-deficiency can be detected by the presence of broad peaks of low intensity in Raman
spectra, that are absent in stoichiometric crystal. Strikingly, the dielectric constant in DIPAB
measured using resonant cavity at the fixed frequency of 2.45 GHz is ~17, while the calculated
static dielectric constant of the ideal DIPAB is low (~2-3). Our results suggest that the much
large measured dielectric constant is due to the Br-deficiency in the synthesized DIPAB sample.
Calculations show that Br-deficient crystals cause a drastic increase of the dielectric constant
(~15-20). Using vdW+DF2 method, we demonstrated that the van der Waals forces have a slight
effect on the structural parameters and cause a small shift in the vibrational frequencies, while
the main features of the DIPAB crystal are driven by covalent bonding inside the DIPA
molecules and hydrogen bonds of the molecules with Br.
Acknowledgements
We thank the financial support from the Nebraska EPSCoR program. The research was
performed in part in the Nebraska Nanoscale Facility: National Nanotechnology Coordinated
Infrastructure and the Nebraska Center for Materials and Nanoscience, which are supported by
the National Science Foundation under Award ECCS: 1542182, and the Nebraska Research
Initiative. The first author would like to thank Jordan University of Science and Technology for
financial and technical support.
7

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Supplementary Information
Table S1. Structural properties and spontaneous polarization of the centrosymmetric monoclinic
P21/m (β) and polar monoclinic P2 (α) phases of DIPAB ferroelectric molecular crystal.
1
Bracketed values correspond to values calculated using the vdW+DF2 method.
Space group
P21/m (β)
P2 (α)
1
Empirical formula
C
6
H16 Br N
6
C H16 Br N
Lattice parameter, a (Å)
Lattice parameter, b (Å)
Lattice parameter, c (Å)
7.946±0.09
8.1567±0.06
7.974±0.08
90
7.799±0.1(7.954)
8.067±0.08(8.227)
7.046±0.07(7.188)
90
α
β
γ
(°)
(°)
(°)
116.511±0.23 116.231±0.30
90
90
3
Equilibrium volume, V (Å ) 463.05
Spontaneous polarization,
443.30 (470.43)
22.64
0
2
s
P (ꢀC/cm )
8

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Fig. S1. PXRD pattern of our synthesized DIPAB polycrystalline sample. Peaks correspond to
phase of DIPAB.
α-
(a)
(b)
-1
-1
Fig. S2. Eigenvectors of the vibrational modes at (a) 182.95 cm and (b) 181.41 cm ,
respectively. Red arrows indicate the vibrational modes for different atoms.
References
1
J. Li, Y. Liu, Y. Zhang, H.-L. Cai, and R.-G. Xiong, “Molecular ferroelectrics: where
electronics meet biology”, Phys. Chem. Chem. Phys. 15, 20786 (2013).
2
S. Horiuchi, Y. Tokura “Organic ferroelectrics”, Nat. Mater. 7, 357 (2008).
C.A. Paz de Araujo, G.W. Taylor, “Integrated ferroelectrics”, Ferroelectrics 116, 215 (2011).
H.-Y. Ye, Y. Zhang, S. Noro, K. Kubo, M. Yoshitake, Z.-Q. Liu, H.-L. Cai, D.-W. Fu, H.
3
4
Yoshikawa, K. Awaga, R.-G. Xiong, and T. Nakamura, “Molecule-displacive ferroelectricity in
organic supramolecular solids”, Sci. Rep. , 2249 (2013).
C.R. Bowen, J. Taylor, E. LeBoulbar, D. Zabek, A. Chauhan, and R. Vaish, “Pyroelectric
Materials and Devices for Energy Harvesting Applications”, Energy Environ. Sci. , 3836
2014).
3
5
7
(
6
K. Gao, M. Gu, X. Qiu, X.N. Ying, H.-Y. Ye, Y. Zhang, J. Sun, X. Meng, F.M. Zhang, D. Wu,
H.-L. Cai, and X. S. Wu, “Above-room-temperature molecular ferroelectric and fast switchable
dielectric of diisopropylammonium perchlorate”, J. Mater. Chem. C , 9957 (2014).
2
7
M. Zirkl, A. Sawatdee, U. Helbig, M. Krause, G. Scheipl, E. Kraker, P.A. Ersman, D. Nilsson,
D. Platt, P. Bodo, S. Bauer, G. Domann, and B. Stadlober, “An All-Printed Ferroelectric Active
Matrix Sensor Network Based on Only Five Functional Materials Forming a Touchless Control
Interface”, Adv. Mater. 23, 2069 (2011).
9

ACCEPTED MANUSCRIPT
8
D.-W. Fu, W. Zhang, H.-L. Gai, J.-Z. Ge, Y. Zhang, and R.-G. Xiong, “Diisopropylammonium
chloride: a ferroelectric organic salt with a high phase transition temperature and practical
utilization level of spontaneous polarization”, Adv. Mater. 23, 5658 (2011).
9
D.-W. Fu, H.-L. Cai, Y. Liu, Q. Ye, W. Zhang, Y. Zhang, X.-Y. Chen, G. Giovannetti, M.
Capone, J. Li, and R.-G. Xiong, “Diisopropylammonium Bromide Is a High-Temperature
Molecular Ferroelectric Crystal”, Science 339, 425 (2013).
1
0
A. Piecha, A. Gagor, R. Jakubas, and P. Szklar, “Room-temperature ferroelectricity in
diisopropylammonium bromide”, CrystEngCommon 15, 940 (2013).
1
1
Kaige Gao, Chuang Liu, Zepeng Cui, Jiansheng Zhu, Hong-Ling Cai and X. S. Wu, “Room-
temperature growth of ferroelectric diisopropylammonium bromide with 12-crown-4 addition”,
CrystEngComm 17, 2429-2432 (2015)
J.F. Scott, “Applications of Modern Ferroelectrics”, Science 315, 954 (2007).
S. Horiuchi, Y. Tokunaga, G. Giovannetti, S. Picozzi, H. Itoh, R. Shimano, R. Kumai, and Y.
.
1
1
2
3
Tokura, “Above-room-temperature ferroelectricity in a single-component molecular crystal”,
Nature 463, 789 (2010).
1
4
M. Veithen, X. Gonze, and P. Ghosez, “First-Principles Study of the Electro-Optic Effect in
Ferroelectric Oxides”, Phys. Rev. Lett. 93, 187401 (2004).
1
5
Shashi Poddar, Haidong Lu, Jingfeng Song, Om Goit, Shah Valloppilly, Alexei
Gruverman and Stephen Ducharme, “Fabrication of diisopropylammonium bromide aligned
microcrystals with in-plane uniaxial polarization”, J. Phys. D: Appl. Phys. 49, 505305 (2016).
1
6
Haidong Lu , Tao Li , Shashi Poddar , Om Goit , Alexey Lipatov , Alexander Sinitskii ,
Stephen Ducharme , and Alexei Gruverman, “Statics and Dynamics of Ferroelectric Domains in
Diisopropylammonium Bromide”, Adv. Mater. 27, 7832-7838 (2015)
.
1
7
, ,
Shradhanjali Sahoo, T.R. Ravindran , Sharat Chandra, R.M. Sarguna, B.K. Das, T.N.
Sairam, V. Sivasubramanian, C. Thirmal, P. Murugavel, “Vibrational spectroscopic and
computational studies on diisopropylammonium bromide”, Biomolecular Spectroscopy 184
,
2
11–219 (2017).
1
8
G. Giovannetti, C. Ortix, M. Marsman, M. Capone, J. van den Brink, and J. Lorenzana,
Proximity of iron pnictide superconductors to a quantum tricritical point”, Nat. Commun.
“
2, 398
(
2011).
1
9
P. Hohenberg, and W. Kohn, “Inhomogeneous electron gas”, Phys. Rev. 136, B864 (1964).
G. Kresse, and D. Joubert, “From ultrasoft pseudopotentials to the projector augmented-wave
2
0
method”, Phys. Rev. B 59, 1758 (1999).
2
1
J.P. Perdew, K. Burke, and M. Ernzerhof, “Generalized Gradient Approximation Made
Simple”, Phys. Rev. Lett. 77, 3865 (1996); Erratum: Phys. Rev. Lett. 78, 1396 (1997).
M. Dion, H. Rydberg, E. Schröder, D.C. Langreth, and B.I. Lundqvist, “Van der Waals Density
2
2
Functional for General Geometries”, Phys. Rev. Lett. 92, 246401 (2004); Erratum: Phys. Rev.
Lett. 95, 109902 (2005).
2
3
K. Lee, E.D. Murray, L. Kong, B. I. Lundqvist, and D.C. Langreth, “Higher-accuracy van der
Waals density functional”, Phys. Rev. B 82, 081101(R) (2010).
2
4
J. Klimes, D.R. Bowler, and A. Michelides, “Van der Waals density functionals applied to
solids”, Phys. Rev. B 83, 195131 (2011) and references therein.
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0

ACCEPTED MANUSCRIPT
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5
Ahmad Alsaad, Chris M. Marin, Nabil Alaqtash, Hsien-Wen Chao, Tsun-Hsu Chang, Chin Li
,
Cheung, A. Ahmad, I.A. Qattan, and Renat F. Sabirianov “Crystallographic data and vibrational
modes of DIPAB crystal”, Data in Brief and the text “submitted”.
2
6
K. Gao, C. Liu, Z. Cui, C. Xu, J. Zhu, L. Gao, H.-L. Cai, and X. S. Wu, “A series of high-
temperature molecular ferroelectric crystals: chlorine doped diisopropylammonium bromide”, J.
Mater. Chem. C , 1959 (2016).
A. Alsaad, I. A Qattan , A. A. Ahmad , N. Al-Aqtash and R. F. Sabirianov, “Structural and
4
2
7
electronic properties of Diisopropylammonium bromide molecular ferroelectric crystal”, IOP
Conf. Series: Materials Science and Engineering 92, 012017 (2015).
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ACCEPTED MANUSCRIPT
•
Diisopropylammonium bromide (DIPAB) molecular ferroelectric crystals were synthesized and
2
examined to exhibit a large electric polarization (~23ꢀC/cm ).
•
FT-IR and Raman vibrational spectra suggests the presence of disorder in the synthesized
crystals as indicated by the presence of broad features in the Raman spectrum.
•
•
The bromine (Br) deficiency strongly affects the electric properties of α-DIPAB.
Our DFT-based calculations show that Br vacancies drastically alter the strength and nature of
crystal bonding, as well as vibrational spectra and dielectric constant of the material.
•
Our data pave the way for further investigations and provide a deeper insight into structural,
dielectric and lattice dynamical properties of this novel polar molecular crystal.
.
•
Our data offers an open invitation for other researchers from chemical and physical
communities who are interested in molecular ferroelectric crystals, in general, and DIPAB
crystal, in particular, to collaborate to dig deeper into structural, chemical and physical properties
of this novel polar molecular crystal.
•
Several previous experiments were performed on the P2 (α) and P21/m (β) phases. Our data
1
represents experimental investigation and first-principles modeling of P2 (α) polar phase. We
1
found an excellent agreement between experimental data and computational data on structural,
dielectric and lattice dynamical properties of P2 (α) phase. As a result, we believe that our data
1
could be potentially used for designing future experiments and that our theoretical model could
serve as a benchmark for future computational models that could be used to initiate new
experiments on DIPAB ferroelectric crystal.