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Ternary sulfides BaLa2S4 and CaLa2S4 as promising photocatalytic water splitting and thermoelectric materials: First-principles DFT calculations

Authors: 

M. Batouche, T. Seddik, Tuan V. Vu, Dat D. Vo, Hien D. Tong*, D.M. Hoat, O.Y. Khyzhun

Source title: 
International Journal of Hydrogen Energy, 2019 (ISI)
Academic year of acceptance: 
2019-2020
Abstract: 

Both ternary sulfides, BaLa2S4 and CaLa2S4, are found to possess a suitable band gap for absorbing visual light; moreover, the ECB and EVB are at right positions allowing the photo-generated electron/hole pairs to split water. The valence band of BaLa2S4 (CaLa2S4) are characterized by high peaks at −1 eV and −2 eV, and strong hybridization of S/La-p and Ba-s (Ca-s/p) states. These features help to enhance the separation of electron/hole pairs. Meanwhile, the conduction band has high peak at 3 eV, which is mostly constructed by hybridization of La-f, La-d and Ba-s (Ca-s/p) states. The conduction band's smooth dispersion is favorable for inter-band transition, thus it enhances the absorption rate of two considered compounds. The Ba/Ca/La–S bonds are predominantly covalent with electronegativity difference of about 31–38%. The large difference in effective mass between electron and hole enhances the separation of electron/hole pairs. CaLa2S4 and BaLa2S4 are p-type semiconductors with positive thermopower S of about 229.8 10.png and 234.8 10.png, respectively, at Fermi level (μ = 0) and temperature 300 K. Both materials show good thermoelectric performance for hole concentration being in the range 1 × 1019–1x1021 cm-3. The electronic figure of merit ZTe marks the highest value of about 0.95 and 0.97 at 2 × 1019 cm-3 for CaLa2S4 and BaLa2S4, respectively.