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Organic ferroelectrics are desirable for the applications in the field of wearable electronics due to their eco-friendly process-ability, mechanical flexibility, low processing temperatures, and lightweight. In this work, we use five organic groups as substitution for organic cation and study the effects of organic cations on the structural stability, electronic structure, mechanical properties and spontaneous polarization of metal-free perovskite A-NH 4-(PF 6) 3( A= MDABCO, CNDABCO, ODABCO, NODABCO, SHDABCO) through first-principles calculations. Firstly, the stabilities of the five materials are calculated by molecular dynamics simulations, and the energy values of all systems are negative and stable after 500 fs, which demonstrates the stabilities of the five materials at 300 K. The electronic structure calculation shows that the organic perovskite materials have wide band gap with a value of about 7.05 eV. The valence band maximum (VBM) and Cconduction band minimum (CBM) are occupied by different elements, which is conductive to the separation of electrons and holes. We find that organic cations have an important contribution to the spontaneous polarization of materials, with a contribution rate over 50%. The presence of hydrogen atoms in the substituting groups (MDABCO, ODABCO) enhances the hydrogen bond interaction between the organic cations and
${\rm PF}_6^- $ and increases the displacement of the organic cation, resulting in an increase in the contribution of the polarization of the organic cation to the total polarization. In addition, we observe large piezoelectric strain components, the calculated value of d 33is 36.5 pC/N for CNDABCO-NH 4-(PF 6) 3, 32.3 pC/N for SHNDABCO-NH 4-(PF 6) 3, which is larger than the known value of d 33of MDABCO-NH 4-I 3(14pC/N). The calculated value of d 14is 57.5 pC/N for ODABCO-NH 4-(PF 6) 3, 27.5 pC/N for NODABCO-NH 4-(PF 6) 3. These components are at a high level among known organic perovskite materials and comparable to many known inorganic crystals. The large value of d 14is found to be closely related to the large value of elastic compliance tensor s 44. The analysis of Young’s modulus and bulk’s modulus shows that these organic perovskite materials have good ductility. These results indicate that these organic materials are excellent candidates for future environmentally friendly piezoelectric materials.
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Keywords:
- metal-free perovskites/
- first-principles calculations/
- piezoelectricity/
- spontaneous polarization
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] -
Material Method a/Å α/(°) V/Å3 MDABCO-NP3 PBE 7.89(0.57%) 84.91(0.06%) 485.51 PBE+D3 7.73(–1.46%) 84.55(–0.36%) 478.25 Exp 7.84 84.86 496.46 SHDABCO-NP3 PBE 7.93 83.84 489.86 PBE+D3 7.74 83.18 483.46 NODABCO-NP3 PBE 7.95 83.74 493.15 PBE+D3 7.84 81.25 485.65 ODABCO-NP3 PBE 7.85 85.2 478.75 PBE+D3 7.75 83.65 475.21 CNDABCO-NP3 PBE 10.58 85.21 477.19 PBE+D3 9.28 83.48 486.48 
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Materials PA PS PA/PS SHDABCO-NP3 2.4 3.8 0.64 NODABCO-NP3 2.6 4.2 0.63 ODABCO-NP3 4.3 6.0 0.71 MDABCO-NP3 4.3 6.3 0.68 CNDABCO-NP3 5.7 9.4 0.61 DownLoad:
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Materials C11 C33 C44 C12 C13 C14 C25 B G E B/G ν MDABCO-NP3 32.9 15.9 8.2 15.9 16.3 0.8 0.1 21.4 8.2 21.8 2.6 0.3 ODABCO-NP3 21.9 7.2 6.7 7.2 14.4 0.2 0.4 18.4 3.6 10.2 2.8 0.3 CNDABCO-NP3 35.2 19.4 6.6 19.4 22.8 0.6 1.3 25.7 6.7 18.4 4.0 0.4 SHDABCO-NP3 32.4 21.8 8.6 21.8 24.1 4.8 4.4 25.9 7.3 20.1 4.1 0.4 NODABCO-NP3 36.2 19.7 4.4 19.7 19.7 0.3 0.4 25.0 5.9 16.5 4.5 0.4 DownLoad:
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Materials d11 d22 d33 d14 d15 d31 MDABCO-NP3 –2.9 –2.6 2.0 –6.3 –1.0 3.0 ODABCO-NP3 –5.5 –0.9 7.4 –57.5 –28.9 0.9 CNDABCO-NP3 –1.3 –2.7 36.5 –7.9 –1.6 17.0 SHDABCO-NP3 –18.2 –20.9 32.3 –10.6 –41.6 27.2 NODABCO-NP3 –0.8 –0.4 7.1 27.5 –21.8 6.18 DownLoad:
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Materials e11 e22 e33 e14 e15 e31 MDABCO-NP3 –3.5 –3.0 2.4 4.5 –0.6 4.9 ODABCO-NP3 –2.1 –0.5 3.5 8.1 –1.7 9.9 CNDABCO-NP3 –1.9 –4.7 34.7 4.7 –0.8 9.7 SHDABCO-NP3 –5.2 –6.6 7.3 4.3 –21.9 6.5 NODABCO-NP3 –1.6 –0.5 10.5 8.9 –10.7 16.8 DownLoad:
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Materials s11 s33 s44 s12 s13 s14 s25 MDABCO-NP3 48.8 49.8 130.3 –16.8 –16.7 3.2 0.6 ODABCO-NP3 38.4 57.2 247.3 –9.0 –17.6 18 45.5 CNDABCO-NP3 56.9 85.4 157.3 –8.8 –35.7 –5.5 13.3 SHDABCO-NP3 124.7 142.4 218.9 –37.0 –79.2 –60.1 5.0 NODABCO-NP3 46.8 51.2 199.0 –16.6 –17.2 17.1 19.9 DownLoad:
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[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48]
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