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Ternary layered nitrides have received widespread attention due to their unique electrical, optical and optoelectronic properties, which are promising for the fabrication of low-cost and high-efficiency optoelectronic materials, solar cell materials and photocatalysts. Although there is a lack of experimental reports on BaTiN2 so far, BaZrN2 and BaHfN2 have been synthesized experimentally by solid state methods. However, their optical and electrical transport properties have not been investigated systematically. This work is to systematically investigates the mechanical, electronic, optical absorption, carrier transport, and dielectric response properties of BaMN2 (M = Ti, Zr, Hf) nitrides through first-principles calculations based on density functional theory. Due to the quasi-two-dimensional layered arrangement of [MN2]2– slabs, the ionic bonds between Ba2+ and N3–, and the weak interactions between the slabs, the deformation along this direction is most likely to occur under the action of external stress. BaMN2 nitrides exhibit significant anisotropic physical properties. Firstly, the mechanical properties of BaMN2, such as bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio, show prominent anisotropy. The lower modulus, higher Poisson’s ratios and Pugh’s modulus ratios indicate good flexibility of the BaMN2 nitrides. In addition, BaMN2 has indirect bandgap values (1.75–2.25 eV) within the visible-light energy range, which meets the basic requirement for the band gap of a photocatalyst for water splitting (greater than 1.23 eV). Moreover, BaMN2 has suitable band-edge positions. The appropriate bandgap values and band-edge positions indicate their broad application prospects in the absorber layer of solar cells and photocatalytic water decomposition. Due to the significant difference in the effective mass of its charge carriers between different directions, BaMN2 exhibits ultrahigh anisotropic carrier mobility (on the order of 103 cm2⋅s–1⋅v–1) and lower exciton binding energy. At the same time, there are significant differences in atomic arrangement and bonding interactions between the in-plane direction and out of plane direction, resulting in high anisotropic visible-light absorption coefficient (on the order of 105 cm–1) in the low energy region. In contrast, the increase of the opportunity for electrons to transition from occupied to unoccupied states leads to more complex light absorption and relatively reduced anisotropy in higher energy region. Furthermore, the special layered structure has lower polarizability and higher vibration frequency along the vertical direction perpendicular to the [MN2]2– layers, rendering BaMN2 nitrides show high dielectric constants. These excellent anisotropic mechanical, optoelectronic, and transport properties allow BaMN2 layered nitrides to be used as promising semiconductor materials in the fields of optoelectronics, photovoltaics, and photocatalysis.
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Keywords:
- nitrides /
- carrier mobility /
- anisotropy /
- first-principles study
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Materials C11/GPa C12/GPa C13/GPa C22/GPa C23/GPa C33/GPa C44/GPa C55/GPa C66/GPa BaTiN2 180.639 126.136 56.702 180.639 56.702 121.448 38.493 38.493 118.834 BaZrN2 151.829 110.797 66.919 151.829 66.919 129.396 37.723 37.723 95.162 BaHfN2 163.876 118.407 69.072 163.876 69.072 130.419 37.811 37.811 103.077 Materials BV/GPa BR/GPa B GV GR G/GPa Y/GPa ν B/G BaTiN2 106.870 95.480 101.175 55.380 42.420 48.900 126.253 0.294 2.070 BaZrN2 102.480 98.630 100.555 46.680 36.539 41.610 109.580 0.318 2.420 BaHfN2 107.920 102.211 105.066 49.180 38.366 43.773 115.194 0.317 2.400 
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Material Carrier m*/m0 Ei/eV μ/(cm2·s–1·V–1) x/y z x/y z x/y z BaTiN2 Electron 0.237 29.929 –7.366 –4.159 7439.406 0.088 Hole 0.536 2.560 –8.141 –5.514 791.781 23.277 BaZrN2 Electron 0.229 32.657 –7.652 –2.399 6313.601 0.225 Hole 0.400 5.435 –8.017 –4.669 1426.402 5.267 BaHfN2 Electron 0.223 30.268 –7.650 –0.679 7286.037 3.429 Hole 0.415 3.608 –7.870 –3.731 1457.158 23.152
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Material $ {\varepsilon }_{{\mathrm{e}}{\mathrm{l}}{\mathrm{e}}} $ $ {\varepsilon }_{{\mathrm{i}}{\mathrm{o}}{\mathrm{n}}} $ $ {\varepsilon }_{{\mathrm{r}}} $ x/y z x/y z BaTiN2 10.59 7.48 35.70 18.40 39.48 BaZrN2 8.30 7.88 39.08 18.61 40.42 BaHfN2 7.71 7.46 34.37 16.32 35.98
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BaTiN2 BaZrN2 BaHfN2 x/y z $ {Z}^{*} $ x/y z $ {Z}^{*} $ x/y z $ {Z}^{*} $ Ba 2.884 3.094 2.954 2.687 3.233 2.869 2.751 3.130 2.877 M 5.355 2.689 4.466 4.811 3.362 4.328 4.617 3.098 4.111 N1 –2.611 –4.357 –3.193 –2.582 –4.839 –3.334 –2.613 –4.552 –3.259 N2 –5.650 –1.433 –4.244 –4.926 –1.764 –3.872 –4.763 –1.672 –3.733
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Mode Symmetry Active Polarization BaTiN2 BaZrN2 BaHfN2 $ {\omega }_{\lambda } $ $ \widetilde{{Z}_{\lambda }^{*}} $ $ {\omega }_{\lambda } $ $ \widetilde{{Z}_{\lambda }^{*}} $ $ {\omega }_{\lambda } $ $ \widetilde{{Z}_{\lambda }^{*}} $ 1-2 Eu IR x-y 119 0.52 67 0.34 62 0.24 3-4 Eg Raman x-y 80 0 73 0 76 0 5 A2u IR z 110 0.52 99 0.43 89 0.30 6 A1g Raman z 115 0 109 0 109 0 7-8 Eg Raman x-y 225 0 157 0 139 0 9 A1g Raman z 285 0 222 0 166 0 10-11 Eu IR x-y 286 0.23 204 0.31 213 0.48 12-13 Eg Raman x-y 336 0 262 0 234 0 14 B1g Raman z 300 0 311 0 325 0 15-16 Eu IR x-y 332 6.10 359 4.38 363 3.84 17 A2u IR z 496 0.04 462 0.69 452 0.78 18-19 Eg Raman x-y 560 0 541 0 572 0 20 A2u IR z 682 2.90 588 3.07 605 2.53 21 A1g Raman z 769 0 679 0 683 0
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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] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66]
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