Article Cite This: Chem. Mater. 2018, 30, 4597−4608
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Ferroelectricity and Ferroelasticity in Organic Inorganic Hybrid (Pyrrolidinium)3[Sb2Cl9] Martyna Wojciechowska,† Anna Gągor,‡ Anna Piecha-Bisiorek,*,† Ryszard Jakubas,† Agnieszka Ciżman,§ Jan K. Zaręba,⊥ Marcin Nyk,⊥ Piotr Zielinś ki,∇ Wojciech Medycki,# and Andrzej Bil† †
Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland W. Trzebiatowski Institute of Low Temperature and Structure Research PAS, P.O. Box 1410, 50-950 Wrocław, Poland § Division of Experimental Physics, Faculty of Fundamental Problems of Technology, University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50−370 Wrocław, Poland ⊥ Advanced Materials Engineering and Modelling Group, Faculty of Chemistry, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland ∇ H. Niewodniczański Institute of Nuclear Physics PAS, Radzikowskiego 152, 31-342 Kraków, Poland # Institute of Molecular Physics, PAS, M. Smoluchowskiego 17, 60-179 Poznań, Poland
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‡
S Supporting Information *
ABSTRACT: Perovskite-like materials exhibit desirable photophysical and electric properties that make them suitable for a remarkable breadth of applications in electronics and physics. In this contribution, we report on the multiphase ferroelectric and ferroelastic phenomena in a pyrrolidiniumbased hybrid metal−organic material: (C4H8NH2)3[Sb2Cl9]. The title compound is the first pyrrolidinium derivative within the halobismuthates(III) and haloantimonates(III) families that is featured by the ferroelectric property. From a structural point of view, the crystal structure is built of [Sb2Cl9]3−∞ perovskite-like layers, interdigitated by layers of pyrrolidinium cations. The rich solid-state dynamics of pyrrolidinium cations endowed (C4H8NH2)3[Sb2Cl9] with a complex sequence of temperature-dependent phase transitions. Remarkably, polar properties have been found to occur in all six phases, including room-temperature Phase I. Insights from variable-temperature single-crystal X-ray diffraction, dielectric spectroscopy, and T1 spin−lattice relaxation measurements revealed the general mechanism of most phase transitions, as related to the progressive ordering of nonequivalent pyrrolidinium cations. Noncentrosymmetry is probed by room-temperature second harmonic generation (SHG), while the ferroelectric property was evidenced through P(E) and dielectric measurements. The experimental values of spontaneous polarization were justified and analyzed in the context of theoretical values derived from quantum-chemical calculations. Optical measurements show that the integrity of the sample survives all of the phase transitions, despite sometimes significant deformations of the unit cell. The changes of symmetry associated with structural phase transitions are accompanied by an intriguing evolution of the ferroelastic domain structure with temperature.
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barium titanate (BTO) or lead zirconate titanate (PZT).9 Their unique three-dimensional structure of corner-sharing MX6 octahedra enclosing 12-coordinate voids is responsible for their excellent physical properties and, thus, has received a tremendous interest from the viewpoints of fundamental science and applications.10,11
INTRODUCTION
The current global scientific trend of the search for new, environmentally friendly, smart materials for photoelectronics and photovoltaics among hybrid, perovskite-like materials is a vast discipline that has promoted a rapid progress over the past decade.1−5 The focus on perovskites, described by the general formula AMX3 (where A = organic cation, M = metal, and X = Cl, Br, I) has evolved over time, to encompass a multitude of aspects of synthetic and physical chemistry.6−8 Despite the presence of toxic metals, the greatest commercial development in this area is reserved mainly to inorganic ceramics such as © 2018 American Chemical Society
Received: March 5, 2018 Revised: June 22, 2018 Published: June 22, 2018 4597
DOI: 10.1021/acs.chemmater.8b00962 Chem. Mater. 2018, 30, 4597−4608
Article
Chemistry of Materials Table 1. Experimental Data for PCA Phase I chemical formula Mr crystal system, space group temperature (K) unit-cell parameters a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) V primitive cell Z radiation type μ (mm−1) crystal size (mm)
8.8458(3) 8.8458(3) 30.2440(14) 90 90 120 2049.48(17) 1/3 V 3 Mo Kα 2.86 0.21 × 0.18 × 0.01
No. of [I > 2σ(I)] reflections measured independent observed Rint (sin θ/λ)max (Å−1)
6692 1332 870 0.025 0.694
R[F2 > 2σ(F2)] wR(F2) S No. of reflections No. of parameters No. of restraints H-atom treatment (Δ/σ)max ρmax (e Å−3) ρmin (e Å−3) absolute structure absolute structure parameter
C12H30Cl9N3Sb2 778.94 trigonal, R3m 255
Phase II Crystal Data C12H30Cl9N3Sb2 778.94 trigonal, P31 225 8.8499(2) 8.8499(2) 30.1715(11) 90 90 120 2046.46(12) 1V 3 Mo Kα 2.90 0.21 × 0.18 × 0.01 Data Collection
19971 6443 3962 0.034 0.695 Refinement 0.061 0.052 0.194 0.119 1.12 0.98 1332 6443 53 324 16 216 H-atom parameters constrained H-atom parameters constrained 0.916 0.033 0.67 0.68 −0.56 −0.56 refined as an inversion twin refined as an inversion twin 0.45 (13) 0.37 (8)
Phase IV C12H30Cl9N3Sb2 778.94 monoclinic, C2 208 14.8102(11) 9.1317(8) 30.110(4) 90 90.189(8) 90 4072.1(7) 1/2 V 6 Mo Kα 2.91 0.21 × 0.18 × 0.01
17382 6855 4263 0.071 0.610 0.127 0.360 1.16 6855 374 215 H-atom parameters constrained 0.358 4.60 −1.58 refined as an inversion twin 0.58 (17)
[M4X18].6−20 Despite a wide variety of the anionic forms, the ferroelectric properties were found to appear only in salts characterized by 0D and 2D anionic layers. Organic−inorganic hybrids based on five-membered nonaromatic heterocycles such as pyrrolidine and the substituted analogue, N-methylpyrrolidine, exhibiting ferroelectric properties are quite rare. Until now, only several such examples are known: (pyrrolidinium)[MnCl 3 ] (T c = 295 K) and (pyrrolidinium)[MnBr3] (Tc = 219 K).21,22 As it was stated, both compounds exhibit intense red luminescence under a UV excitation, as well as ferroelectric properties. Moreover, in the case of the bromide analogue, a weak ferromagnetism is also observed. In the haloantimonates(III) and halobismuthates(III) family, only two compounds can be treated as a representatives of lead-free perovskite halides (N-methylpyrrolidinium)3[Sb2Cl9] (Tc = 322 K) and (N-methylpyrrolidinium)3[Sb2Br9] (Tc = 323 K). Those compounds were found to show large ferroelectric polarizations (5.2 μC cm−2 (Cl) and 7.6 μC cm−2 (Br), respectively) and pronounced semiconducting performances.23,24
It is the rich diversity of the anionic substructures (from zero-, through one-, two-, or even three-dimensional architecture) and isoelectronicity with Sn(II) and Pb(II) that are mainly responsible for the huge interest of the Sb(III) or Bi(III) halides group. 12,13 Haloantimonates(III) and halobismuthates(III) of the general formula RaMbX3b+a, (where R denotes organic cations, M stands for Sb(III) or Bi(III), and X = Cl, Br, I) have garnered the wide interest of the scientific community as they combine many desirable features, e.g., facile synthesis and processing, biocompatibility, and cost-effectiveness with the desired electrical and optical properties.14,15 There is a huge diversity of chemical compositions among halontimonates(III) and halobismuthates(III). Nevertheless, ferroelectricity is limited to few of them only, e.g., RMX4, R3M2X9, R2MX5, and R5M2X11.16 Many reports have been devoted to the crystals with the R3M2X9 composition, which are characterized by three terminal halogen atoms and three bridging ones. The [MX6] octahedra can form either infinite one-dimensional (1D) double chains,17 two-dimensional (2D) layers,18 discrete bioctahedral (0D) 19 or four-octahedral (0D) units 4598
DOI: 10.1021/acs.chemmater.8b00962 Chem. Mater. 2018, 30, 4597−4608
Article
Chemistry of Materials
the temperature range of 300−875 K with a ramp rate of 5 K min−1. The scans were performed in flowing nitrogen (flow rate = 1 dm3 h−1). Dielectric Studies. The complex dielectric permittivity (ε* = ε′ − iε″) measurements were conducted on PCA single crystal with the use of an Agilent E4980A Precision LCR Meter between 100 K and 300 K in the frequency range between 135 Hz and 2 MHz. The overall errors were
