Thermal-Induced Ferroelastics in Two Lead-Free Organic–Inorganic Hybrid Perovskites

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLES14 Nov 2022Thermal-Induced Ferroelastics in Two Lead-Free Organic–Inorganic Hybrid Perovskites Pei-Zhi Huang, Hao-Fei Ni, Chang-Yuan Su, Meng-Meng Lun, Hai-Feng Lu, Da-Wei Fu and Qiang Guo Pei-Zhi Huang Institute for Science and Applications of Molecular Ferroelectrics, Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Zhejiang Normal University, Jinhua, Zhejiang 321004 , Hao-Fei Ni Institute for Science and Applications of Molecular Ferroelectrics, Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Zhejiang Normal University, Jinhua, Zhejiang 321004 , Chang-Yuan Su Ordered Matter Science Research Center, Jiangsu Key Laboratory for Science and Applications of Molecular Ferroelectrics, Southeast University, Nanjing, Jiangsu 211189 , Meng-Meng Lun Ordered Matter Science Research Center, Jiangsu Key Laboratory for Science and Applications of Molecular Ferroelectrics, Southeast University, Nanjing, Jiangsu 211189 , Hai-Feng Lu *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Institute for Science and Applications of Molecular Ferroelectrics, Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Zhejiang Normal University, Jinhua, Zhejiang 321004 , Da-Wei Fu *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Institute for Science and Applications of Molecular Ferroelectrics, Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Zhejiang Normal University, Jinhua, Zhejiang 321004 and Qiang Guo *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Institute for Science and Applications of Molecular Ferroelectrics, Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Zhejiang Normal University, Jinhua, Zhejiang 321004 https://doi.org/10.31635/ccschem.022.202202332 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Lead-based organic–inorganic hybrids occupy a niche in the field of optoelectronics due to exceptional semiconducting properties and potential ferroelasticity. Nevertheless, the possible toxicity of lead restricts their widespread application to a certain extent. Herein, two new lead-free ferroelastic semiconductors are reported: [DMMClEA]3Bi2Br9 (compound 1) and [DMMClEA]3Sb2Br9 (compound 2) (DMMClEA = N-(chloromethyl)-N,N-dimethylethylammonium), in which the inorganic framework neatly arranges with [Bi2Br9]3−/[Sb2Br9]3− polyhedrons shared by face, forming an A3B2X9-type structure. Both compounds 1 and 2 possess two-step phase transitions, including a 3 ¯ mF2/m-type ferroelastic phase transition, based on the Aizu rule. In addition, dual dielectric switches endow the application toward sensor devices. This finding enriches A3B2X9-type zero-dimensional hybrid ferroelastics and provides an approach to designing high-performance, lead-free perovskite semiconductors with dielectric functionality. Download figure Download PowerPoint Introduction Phase-transition materials can be reversed by the stimulations of light, electricity, magnetism, temperature, pressure, and so on, making them feature a broad range of applications related to optoelectrical components, energy storage equipment, communication engineering, medical defense, and so on.1–10 Among diverse types of phase-transition materials, ferroelastics with rich physical properties have attracted the extensive attention of researchers.11–21 Meanwhile, organic–inorganic hybrid compounds (OIHCs) with structural flexibility provide a favorable design platform for the construction of ferroelastics, such as ABX3-type perovskites. Particularly, lead-based perovskites have dominated optoelectronic research in the past decades.22–32 However, the presence of poisonous lead is incompatible with the application demands. Therefore, developing ideally lead-free materials with high performance is imperative. Considering environmental friendliness, the number of lead-free OIHCs has proliferated.33–45 Especially, the Bi/Sb-based OIHCs exist as a perovskite-like structure of AaBbX3b+a (A = organic cations, B = Bi or Sb, X = Cl, Br, I and a, b = 1, 2, 3…),46–52 showing rich structural diversity. Inorganic frameworks are modulated into zero-dimensional,46 one-dimensional,51 two-dimensional,21 and three-dimensional53 structures by adjusting organic cations, among which, the A3Bi2X9 type is the most general architecture. Multifunctional Bi/Sb-based ferroelastics are successfully realized through structural design. For example, Zhang et al.54 designed a Bi-based organic–inorganic hybrid ferroelastic semiconductor (DMTBA)3Bi2Br9 (DMTBA = N,N-dimethyl-tert-butylammonium) with double dielectric switches, which is triggered by introducing two methyl groups into tert-butylammonium. However, the dielectric constant transition before and after phase change in (DMTBA)3Bi2Br9 is relatively small. Furthermore, Bi-based organic–inorganic hybrid ferroelastics have been rarely realized at the current stage. Inspired by previous work, two organic–inorganic hybrid ferroelastic semiconductors with two-step phase transitions are reported here: [DMMClEA]3Bi2Br9 (compound 1) and [DMMClEA]3Sb2Br9 (compound 2) (DMMClEA = N-(chloromethyl)-N,N-dimethylethylammonium). The experimental results show that both compounds can successfully achieve the multifunctional feature. Therefore, two-step phase transitions were shown at higher temperatures (311 and 339 K for compound 1; 316 and 336 K for compound 2) on heating. Specifically, the first phase transitions of compounds belong to the 3 ¯ mF2/m-type ferroelastic phase transition according to the Aizu rule. Furthermore, they also exhibit semiconductor characteristics (2.82 and 2.89 eV). Consequently, the excellent ferroelastic properties of the two compounds endow applications toward optoelectronic, spintronic, and sensor devices. Experimental Methods Synthesis of compound 1 For the synthesis, the reaction steps are shown in Supporting Information Scheme S1. Bromochloromethane (10 mmol) was added dropwise to N,N-dimethylethylamine (10 mmol) in 40 mL of anhydrous acetonitrile, and a colorless transparent solution was obtained after stirring and refluxing for 24 h. Eventually, the quaternary ammonium salt ([DMMClEA]Br) was obtained by rotary evaporation. Stoichiometric amounts of [DMMClEA]Br (0.608 g, 3 mmol) and BiBr3 (1.346 g, 3 mmol) were mixed while stirring in deionized water (10 mL) and HBr (40% in deionized water, 10 mL). Light yellow crystals of compound 1 were obtained through evaporation at 308 K for 1 week. Synthesis of compound 2 Stoichiometric amounts of [DMMClEA]Br (0.608 g, 3 mmol) and Sb2O3 (0.437 g, 1.5 mmol) were mixed while stirring in deionized water (10 mL) and HBr (40%, 20 mL). Orange yellow crystals were obtained through evaporation at 308 K for 1 week. Single-crystal X-ray diffraction Variable-temperature single-crystal X-ray diffraction (SXRD) information was gathered by a Bruker APEX-II CCD (Bruker, Karlsruhe, Baden-Württemberg, Germany) with Mo-Kα radiation (λ = 0.71073 Å) at 223, 325, and 350 K for the two compounds. The structures were established by direct methods and refined by the full matrix method through the SHELXTL software package. Powder X-ray diffraction Powder X-ray diffraction (PXRD) data for compounds 1 and 2 were obtained on a Bruker D8 Advance03030502 X-ray diffractometer (Bruker, Karlsruhe, Baden-Württemberg, Germany) in the degree range of 5–55° at room temperature. Simulated powder patterns of samples were calculated by Mercury software package with crystallographic information file. Variable-temperature PXRD data for compounds 1 and 2 were collected on a Bruker APEX-II CCD with Cu-Kα radiation (λ = 1.5418 Å) at 295, 325, 355, and 385 K. Differential scanning calorimetry The differential scanning calorimetry (DSC) measurements of 1 and 2 were executed within the temperature range from 200 to 400 K at 20 K·min−1 using a NETZSCH-214 instrument (NETZSCH, Selb, Bavaria, Germany). Ferroelastic measurement The ferroelastic domain was gained by observing the single crystals of compounds 1 and 2 with an Olympus BX51TRF polarizing microscope (Olympus, Tokyo, Japan). Meanwhile, an INSTEC HCC602 (INSTEC, Boulder, Colorado, USA) temperature regulating device was used to control temperature. Dielectric measurements The sheets of 1 and 2 were gained by pressing the powder samples under 10 MPa pressure. Then capacitors for dielectric measurements were made by silver painting. Finally, the dielectric constant curves were collected using a TongHui TH2828A instrument (TongHui, Changzhou, Jiangsu, China) at a temperature range of 170–400 K. Ultraviolet–visible absorbance spectroscopy Ultraviolet–visible (UV–vis) absorbance spectroscopy was measured with powder samples by using a Shimadzu UV-2600 spectrophotometer (Shimadzu, Kyoto, Japan) at room temperature. Theoretical calculations All calculations were performed at the spin-polarized density functional theory (DFT) level with the Vienna Ab Initio Simulation Package.55 The projector-augmented wave method56 and Perdew–Burke–Ernzerhof57 functional were exploited to describe the electron-ion and the exchange-correlation interactions, respectively. The band structure and density of states (DOS) were calculated based on crystal structures at 223 K. A cutoff energy of 500 eV was adopted for all simulations. In the self-consistent calculation, the energy convergence criteria were set to 10−5 eV. The Brillouin zone was sampled using a Monkhorst-Pack mesh of 1 × 1 × 1 k-point grids for energy calculations. Results and Discussion Thermodynamic analysis of phase transition behaviors The design strategy is revealed in Figure 1a: the compounds are a combination of amines containing methyl, ethyl, and methyl chloride groups and Bi/Sb salts. To demonstrate the phase transitions of compounds 1 and 2, DSC were carried out, and the results were obtained as depicted in Figure 1b. For compound 1, two distinct peaks at 311 and 339 K during the heating process and two corresponding peaks at 303 and 335 K during the cooling process are clearly observed, indicating that compound 1 undergoes two reversible first-order phase transitions. Similarly, for compound 2, two pairs of apparent reversible peaks (316 and 336 K on heating, 307 and 331 K on cooling) demonstrate that compound 2 also undergoes two reversible phase transitions. Based on DSC curves, the average changes in entropy (ΔS) are calculated as 11.564 and 3.885 J·mol−1·K−1 for compound 1. Combining the Boltzmann formula ΔS = R ln(N), the values of N are obtained as 4.018 and 1.596 (N is the ratio of possible configurations and R is the gas constant). Similarly, for compound 2, the entropies are 12.854 and 4.384 J·mol−1·K−1, resulting in the values of N of 4.693 and 1.694, reflecting that the phase transitions probably arise from order–disorder transformation of the cations.58 To test the thermal stability of compounds 1 and 2, thermogravimetric analysis (TGA) was implemented ( Supporting Information Figure S1). According to the TGA curves, the decomposition temperatures of compounds 1 and 2 are about 480 and 511 K, respectively, far higher than the phase transition temperatures. In compound 1, the phase below 311 K is named α1 phase, the phase above 339 K is called γ1 phase, and the phase between the 311 and 339 K is labeled as β1 phase for convenience. For compound 2, the phase below 316 K is named α2 phase, the phase above 336 K is called the γ2 phase, and the phase between the 316 and 336 K is labeled as β2 phase. Figure 1 | (a) The design strategy of two ferroelastics with dual phase transitions and semiconductor properties. (b) DSC curves of compound 1 and compound 2. Download figure Download PowerPoint Variable-temperature crystal structures and intermolecular interaction analyses To reveal the process of phase transitions more intuitively, the variable-temperature single-crystal X-ray diffraction was performed. Both compounds belong to the P21/c space group at room temperature, showing an A3B2X9-type zero-dimensional structure (Figure 2a and Supporting Information Figure S2), where a basic unit is composed of the inorganic framework neatly arranging with [Bi2Br9]3−/[Sb2Br9]3− polyhedrons shared by face and three cations. Figure 2 | (a) The packing structure of compound 1. (b) Variable-temperature structures of cations for compound 1 in the α1, β1, and γ1 phases with a vivid description by a ballet dancer. Download figure Download PowerPoint Structural feature analysis is a significant method to determine the process of phase transitions. Compound 1 crystallized in the P21/c space group at low temperature (α1 phase) with the cell parameters: a = 23.280 (3) Å, b = 19.784 (3) Å, c = 16.894 (2) Å, β = 91.360 (3)°, V = 7779.0 (18) Å3, while locating in the P 3 ¯ 1c space group at intermediate temperature (β1 phase) and high temperature (γ1 phase) with equiform lattice parameters ( Supporting Information Table S1). As shown in Figure 2b, all the organic cations are in a steady and ordered stationary state in the α1 phase, while partially disordered in the β1 phase and completely disordered in the γ1 phase. This order–disorder transition is like a ballet dancer: standing (ordered state), gently dancing (partially disordered state) and violently spinning (completely disordered state). For the [Bi2Br9]3− inorganic frameworks, the length of the Br–Bi bond varies from 2.7115 to 3.0729 Å in α1 phase, between 2.705 and 3.0208 Å in the β1 phase, 2.693 and 3.0161 Å in the γ1 phase ( Supporting Information Table S2). Meanwhile, the angles of the Br–Bi–Br have almost no change ( Supporting Information Table S3). Thus, the phase transitions of compound 1 might be stimulated mainly by the order–disorder transformation of the organic cations. In addition, variable-temperature PXRD measurements were executed to further demonstrate the double phase transition properties of both compounds ( Supporting Information Figure S4). The peak positions obviously changed with the temperature increase, especially at about 43° and 50° for compound 1 and 29° and 41° for compound 2. Room-temperature PXRD analyses were further implemented to check the purity of compounds 1 and 2 ( Supporting Information Figure S5). The results show that both compounds are pure phase. The structural parameters of compound 2 is similar to that of 1, and the detailed data are provided in the Supporting Information ( Supporting Information Figures S2 and S3 and Tables S4–S6). The Hirshfeld surfaces map and fingerprint plots ( Supporting Information Figure S6) were recorded to analyze the strength of weak force inside the structure. The deep red spots in the Hirshfeld surfaces represent sites of H···Br hydrogen-bond interactions ( Supporting Information Figure S7). The interactions can be reflected from the two-dimensional fingerprint plots, which have minimum distances (di, de) of (0.985, 1.187) in compound 1, and (1.024, 1.252) in compound 2. In addition, the percentages of the hydrogen-bond interactions are 44.1% for 1 and 43.5% for 2. Obviously, the interactions in compound 1 are stronger than those in 2, proving that the phase transition temperature of compound 1 is higher than that of compound 2. Ferroelasticity According to the structural analysis results, accompanying the space group transformation from P 3 ¯ 1c to P21/c, the phase transitions of both compounds belong to the 3 ¯ mF2/m-type ferroelastic phase transition according to the Aizu rule. The appearance and disappearance of ferroelastic domains can be observed by the variable-temperature polarizing microscope (Figure 3 and Supporting Information Figure S8). For compound 1 in the α1 phase of 293 K, the obvious single domain structure emerges. However, when heating to 325 K, toward β1 phase, the domain structures disappear gradually (Figure 3b). Then, parallel striped domain structures slowly emerge with the temperature decrease (Figure 3c). While continuing to cool, the parallel striped domain structures tardily transform to single-domain structures (Figure 3a). Therefore, the transformations of ferroelastic domains clearly show the crystal symmetry change. In addition, Supporting Information Videos S1 (for compound 1) and S2 (for compound 2) exhibit the whole dynamic conversion process of domain structures in the heating and cooling cycles. Figure 3 | Topography and the evolution of the domain patterns during the temperature cycles by observing single crystal of the compound 1. Download figure Download PowerPoint The spontaneous strain tensor of ferroelastics is determined by its crystal structure. For compound 1, the following calculation matrix (Equation 1) is obtained according to the symmetry transformation of 3 ¯ mF2/m from the high-symmetry phase (trigonal) to the low-symmetry phase (monoclinic): ε i j = [ ε 11 ε 12 ε 13 ε 21 ε 22 ε 23 ε 31 ε 32 ε 33 ] (1) Then, the cell parameters of ferroelastic and paraelastic phases were substituted. Eventually, the total spontaneous strain εss is calculated as 0.72422 by Eq. (2). The detailed calculation process is in the Supplementary Information. Meanwhile, the total spontaneous strain εss is 0.72901 for compound 2. ε s s = ∑ i j ε i j 2 . (2) Dielectric switch characteristics To explore the dielectric properties of compounds 1 and 2, the temperature-dependent permittivity measurements were executed with electrodes (Figure 4c). For compound 1, two pairs of dielectric anomalies are observed at around 311 and 339 K (Figure 4a). As the temperature increases, the permittivity slowly increases until the value reaches about 8, then a dielectric anomaly occurs. The dielectric constant increases rapidly near 339 K. Dielectric anomalies occur at the corresponding temperatures during both the heating and cooling drives, indicating two reversible phase transitions in compound 1. For compound 2, two dielectric anomalies (near 316 and 336 K) also demonstrate a pair of phase transitions (Figure 4d). The dielectric anomalies of compounds 1 and 2 match well with the results of DSC measurements, further demonstrating that two consecutive reversible phase transitions occur in both compounds. Figure 4a,d shows the dielectric constant is temperature-dependent consistently. In Figure 4b,e, it reveals that the dielectric constants of both compounds 1 and 2 are also frequency-dependent. Due to the polarization relaxation characteristics, specifically, the higher the frequency, the lower the dielectric constant. At higher frequencies, the electron polarization adapts immediately to the change in electric field and responds quickly, whereas the dipole steering polarization does not match instantaneously. For compound 1, the dielectric constant is about 23.2 times as large as that before phase transition at 500 Hz frequency, whereas for compound 2 it is about 12.3 times as large. In addition, with the properties of temperature dependence and dielectric switching, compounds 1 and 2 might be used for temperature sensors. Here, the Figure 4f shows the diagram of the potential applications in temperature sensors, which is based on the phase transition characteristics of compound 1 and 2. Once the temperature exceeds the phase transition temperatures, further changes in permittivity results. Figure 4 | Real parts of dielectric constant at 1 MHz in a heating and cooling run with dielectric loss for compound 1 (a) and compound 2 (d). Real parts of dielectric constant at different frequencies in the heating process for compound 1 (b) and compound 2 (e). (c) Illustration of dielectric constant measurements. (f) Diagram of the potential applications of compounds 1 and 2 in temperature sensors. Download figure Download PowerPoint Semiconducting behavior Compounds 1 and 2 also show great semiconductor properties. The solid-state UV–vis absorption spectra at room temperature (Figure 5a and Supporting Information Figure S9a) display obvious absorptions at around 500 and 480 nm for 1 and 2, respectively. According to the Tauc plot, the band gaps are calculated as 2.82 and 2.89 eV, comparable with other organic–inorganic hybrid ferroelastics such as (N,N-dimethylethanolammonium)PbBr3 (3.52 eV).59 Meanwhile, DFT calculations reveal that compounds 1 and 2 are direct band gap semiconductors because the highest point of valence band and the lowest point of conduction band are located at the same point of Brillouin region. The theoretical band gaps are calculated as 2.85 and 2.94 eV for compounds 1 and 2, close to the experimental values (Figure 5b and Supporting Information Figure S9b). In addition, the compounds exhibit different band gaps, which might result from the fact that the inorganic metal skeleton plays a decisive role in the band gap (Figure 5c and Supporting Information Figure S9c). Figure 5 | (a) The UV–vis absorption and corresponding Tauc plots of compound 1. (b) The spin–orbit coupling (SOC) diagram of compound 1. (c) Partial density of states (PDOS) of compound 1. Download figure Download PowerPoint Conclusion Two lead-free hybrid ferroelastic semiconductors were successfully synthesized. They present dual phase transitions and semiconductor properties (2.82 and 2.89 eV). Based on the Aizu rule, the phase transitions belong to the 3 ¯ mF2/m-type ferroelastic phase transition. In addition, with the characteristics of double dielectric switching, compounds 1 and 2 might be applied in temperature sensors. We sincerely hope this work can provide a new strategy for exploring multifunctional and lead-free ferroelastics. Supporting Information Supporting Information is available and includes the calculation process of the spontaneous strain, PXRD patterns, TGA curves, and additional tables of crystal data. Conflict of Interest There is no conflict of interest to report. Funding Information This work was financially supported by the National Natural Science Foundation of China (grant no. 21991141). References 1. Ye H. Y.; Liao W. Q.; Hu C. L.; Zhang Y.; You Y. M.; Mao J. G.; of 2. Y. Y.; H. L.; H. L.; Hybrid with and Y. J. L.; in Y.; Hu C. L.; W. Y. Zhang Y. Zhang W. from Molecular in a Hybrid Zhang Y.; Hu L.; with Zhang M.; in for and Fu J. W. Huang Q.; Y. Based on Liao W. Q.; Hu Y. in a Molecular with 8, Y.; Y. L.; J. Y. Y.; M.; of and in a Molecular Y.; Q.; J. 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