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In this paper, the electronic structures and absorption spectra of LiNbO3 (LN) and Fe:Mg:LiNbO3 crystals are studied by the first-principles under the generalized gradient approximation. The supercell structures of the LN crystal are established with 60 atoms, including four models: pure LN crystal, Fe:LiNbO3 crystal (Fe:LN), Fe:Mg:LiNbO3 crystal with Mg of 2 mol%-3 mol% (Fe:Mg(L):LN), and Fe:Mg:LiNbO3 crystal with Mg of 5.0 mol% (Fe:Mg(E):LN). The electronic structures show that the extrinsic defect levels (within forbidden band) of Fe:LN are contributed by Fe 3d orbital and O 2p orbital, and the band gap of Fe:LN (about 2.85 eV) is narrower than that of LN. For Fe:Mg:LN crystals, the band gap changes to 2.90 eV and 2.81 eV respectively for the Mg ion concentration less than and equal to the threshold (～5.0 mol%). The two absorption peaks at 2.3 eV and 2.6 eV are attributed to the Fe ions in crystal. Moreover, the intensities of these peaks vary with the concentration of Mg ion. It is revealed that the concentration of Mg ion influences the concentrations and the sites of Fe2+ and Fe3+ ions in crystal. From the absorption spectrum, the values of ratio Fe2+/Fe3+ in Fe:Mg(E):LN and Fe:Mg(L):LN can be obtained, and the ratio of first sample is smaller than that of the second one. With the one-center model, one can distinctly deduce that the photoconductivity of Fe:Mg(E):LN is relatively weak compared with that of Fe:Mg(L):LN, but this is inconsistent with many experimental results. One notices the contribution of O 2p orbital to extrinsic defect level in electronic structure. Therefore, it is reasonable to presume that the one-center model is not suitable enough for this condition. Based on the research work, we find that the formations of photoelectrons are related to orbital electron states of iron ions and oxygen atoms at extrinsic defect levels in Fe:LN and Fe:Mg:LN crystals.
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Keywords:
- first-principles /
- LiNbO3 crystal /
- electronic structure /
- absorption spectrum
[1] Kong Y F, Xu J J, Zhang G Y 2005 Multi-function Photoelectric Materials LiNbO3 Crystal (Beijing: Sciences Press) pp173, 174 (in Chinese) [孔勇发, 许京军, 张光寅 2005 多功能光电材料铌酸锂晶体 (北京: 科学出版社)第173, 174页]
[2] Bae S I, Ichikawa J, Shimamura K, Onodera H, Fukuda T 1997 J. Cryst. Growth 180 94
[3] Chen X L, Zhang Y, Ran Q Y 2013 Acta Phys. Sin. 62 037201 (in Chinese) [陈小兰, 张耘, 冉启义 2013 62 037201]
[4] Chen H J, Shi L H, Yan W B, Chen G F, Shen J, Li Y X 2009 Chin. Phys. B 18 2372
[5] Schirmer O F, Thiemann O, Wöhlecke M 1991 J. Phys. Chem. Solids 52 185
[6] Xu C, Yang C H, Zhu C Q, Sun T, Wang R, Xu Y H 2012 Mater. Lett. 67 320
[7] Li X C, Qu D X, Zhao X J, Meng X J, Zhang L L 2013 Chin. Phys. B 22 024203
[8] Chen S L, Liu H D, Kong Y F, Huang Z H, Xu J J 2006 Cryst. Res. Technol. 41 790
[9] Feng H X, Wen J K, Wang H, Wang H F 1990 Appl. Phys. A 51 394
[10] Abrahams S C, Hamilton W C, Reddy J M 1996 Acta Phys. Sin. 45 1852 (in Chinese) [刘建军, 张万林, 张光寅 1996 45 1852]
[11] Bäker A, Donnerberg H, Schirmer O F, Feng X Q 1990 J. Phys.: Condens. Matter 2 6865
[12] Prieto C, Zaldo C 1992 Solid State Commun. 83 819
[13] Liu J J, Zhang W L, Zhang G Y 1996 Solid State Commun. 98 523
[14] Veithen M, Gonze X, Ghosez P 2004 Phys. Rev. Lett. 93 187401
[15] Mamoun S, Merad A E, Guilbert L 2013 Comput. Mater. Sci. 79 125
[16] Tian F H, Liu C B 2006 J. Phys. Chem. B 110 17866
[17] Inbar I, Cohen R E 2004 Mater. Chem. Phys. 83 350
[18] Xu H X, Chernatynskiy A, Lee D, Sinnott S B, Gopalan V, Dierolf V, Phillpot S R 2010 Phys. Rev. B 82 184109
[19] Ellabban M A, Woike T, Fally M, Rupp R A 2005 Europhys. Lett. 70 471
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[1] Kong Y F, Xu J J, Zhang G Y 2005 Multi-function Photoelectric Materials LiNbO3 Crystal (Beijing: Sciences Press) pp173, 174 (in Chinese) [孔勇发, 许京军, 张光寅 2005 多功能光电材料铌酸锂晶体 (北京: 科学出版社)第173, 174页]
[2] Bae S I, Ichikawa J, Shimamura K, Onodera H, Fukuda T 1997 J. Cryst. Growth 180 94
[3] Chen X L, Zhang Y, Ran Q Y 2013 Acta Phys. Sin. 62 037201 (in Chinese) [陈小兰, 张耘, 冉启义 2013 62 037201]
[4] Chen H J, Shi L H, Yan W B, Chen G F, Shen J, Li Y X 2009 Chin. Phys. B 18 2372
[5] Schirmer O F, Thiemann O, Wöhlecke M 1991 J. Phys. Chem. Solids 52 185
[6] Xu C, Yang C H, Zhu C Q, Sun T, Wang R, Xu Y H 2012 Mater. Lett. 67 320
[7] Li X C, Qu D X, Zhao X J, Meng X J, Zhang L L 2013 Chin. Phys. B 22 024203
[8] Chen S L, Liu H D, Kong Y F, Huang Z H, Xu J J 2006 Cryst. Res. Technol. 41 790
[9] Feng H X, Wen J K, Wang H, Wang H F 1990 Appl. Phys. A 51 394
[10] Abrahams S C, Hamilton W C, Reddy J M 1996 Acta Phys. Sin. 45 1852 (in Chinese) [刘建军, 张万林, 张光寅 1996 45 1852]
[11] Bäker A, Donnerberg H, Schirmer O F, Feng X Q 1990 J. Phys.: Condens. Matter 2 6865
[12] Prieto C, Zaldo C 1992 Solid State Commun. 83 819
[13] Liu J J, Zhang W L, Zhang G Y 1996 Solid State Commun. 98 523
[14] Veithen M, Gonze X, Ghosez P 2004 Phys. Rev. Lett. 93 187401
[15] Mamoun S, Merad A E, Guilbert L 2013 Comput. Mater. Sci. 79 125
[16] Tian F H, Liu C B 2006 J. Phys. Chem. B 110 17866
[17] Inbar I, Cohen R E 2004 Mater. Chem. Phys. 83 350
[18] Xu H X, Chernatynskiy A, Lee D, Sinnott S B, Gopalan V, Dierolf V, Phillpot S R 2010 Phys. Rev. B 82 184109
[19] Ellabban M A, Woike T, Fally M, Rupp R A 2005 Europhys. Lett. 70 471
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