First-Principles Study on the Stability and Electronic Properties of Bi-Doped Sr3Ti2O7

doi:10.1016/j.jmst.2016.11.023

Abstract

Abstract:

The electronic and crystal structural properties of Bi-doped Sr₃Ti₂O₇ are studied using the first principles density functional theory (DFT) based on pseudopotentials basis and plane-wave method. Our results show that the formation energy of Bi doping in Site-1 and Site-2 of Sr₃Ti₂O₇ increases with increasing doping concentration. And at the same doping concentration, the formation energy of Bi doping in Site-2 is lower than that in Site-1. The undoped Sr₃Ti₂O₇ is found to be an insulator and its Fermi level stays at the top of the valence band. While the Fermi level of the Bi-doped Sr₃Ti₂O₇ moves into the bottom of conduction band, the system undergoes an insulator-to-metal phase transition. Furthermore, our calculation results demonstrated that the Fermi level of the Bi-doped Sr₃Ti₂O₇ goes deeper into the bottom of conduction band with increasing doping concentration.

Key words: Strontium titanate ceramics, Bi-doping, Phase stability, Electronic properties, First-principles calculations

Yanli Lu, Fang Liu, Xiang Li, Feng Gao, Zheng Chen. First-Principles Study on the Stability and Electronic Properties of Bi-Doped Sr₃Ti₂O₇[J]. J. Mater. Sci. Technol., 2018, 34(5): 891-898.

Figures/Tables 14

Fig. 1. Results of the test for the Ecut convergence.

Fig. 2. Crystal structure of Sr3Ti2O7.

Table 1 Different supercells and doping concentrations

Supercell	Sr	Ti	O	Bi	Total atoms	Doping concentration
1 × 1 × 1	6	4	14	0	24	0
2 × 3 × 1	35	24	84	1	144	0.0278
3 × 1 × 1	17	12	42	1	72	0.0556
1 × 1 × 1	5	4	14	1	24	0.1667

Table 2 Lattice parameters of optimized Sr3-xBixTi2O7 (x = 0, 0.0278, 0.0556, 0.1667)

Sr_3-_xBi_xTi₂O₇	a (nm)	b (nm)	c (nm)
x = 0.0	0.3816	0.3816	1.9955
Site-1 x = 0.0278	0.3935	0.3936	2.0476
Site-2 x = 0.0278	0.3934	0.3935	2.0480
Site-1 x = 0.0556	0.3940	0.3938	2.0451
Site-2 x = 0.0556	0.3934	0.3931	2.0515
Site-1 x = 0.1667	0.3942	0.3942	2.0451
Site-2 x = 0.1667	0.3935	0.3935	2.0524

Fig. 3. Total energy of unit cell with different doping sites at the same concentration.

Table 3 Dopant formation energy of each system at different doping concentrations

Sr_3-_xBi_xTi₂O₇	x = 0.0278	x = 0.0556	x = 0.1667
Site-1 (eV)	2.8385	3.2477	6.1425
Site-2 (eV)	2.7279	3.0465	5.3048

Fig. 4. DOS and PDOS of Sr3Ti2O7: (a) total DOS of Sr3Ti2O7, (b) DOS of Sr, (c) DOS of Ti, (d) DOS of O.

Fig. 5. DOS and PDOS of Sr3-xBixTi2O7 (x = 0.0278) with doping Site-1: (a) total DOS of Sr3-xBixTi2O7 (x = 0.0278), (b) DOS of Ti, (c) DOS of O, (d) DOS of Bi.

Fig. 6. DOS and PDOS of Sr3-xBixTi2O7 (x = 0.0278) with doping Site-2: (a) total DOS of Sr3-xBixTi2O7 (x = 0.0278), (b) DOS of Ti, (c) DOS of O, (d) DOS of Bi.

Fig. 7. DOS and PDOS of Sr3-xBixTi2O7 (x = 0.0556) with doping Site-1: (a) total DOS of Sr3-xBixTi2O7 (x = 0.0556), (b) DOS of Ti, (c) DOS of O, (d) DOS of Bi.

Fig. 8. DOS and PDOS of Sr3-xBixTi2O7 (x = 0.0556) with doping Site-2: (a) total DOS of Sr3-xBixTi2O7 (x = 0.0556), (b) DOS of Ti, (c) DOS of O, (d) DOS of Bi.

Fig. 9. DOS and PDOS of Sr3-xBixTi2O7 (x = 0.1667) with doping Site-1: (a) total DOS of Sr3-xBixTi2O7 (x = 0.1667), (b) DOS of Ti, (c) DOS of O, (d) DOS of Bi.

Fig. 10. DOS and PDOS of Sr3-xBixTi2O7 (x = 0.1667) with doping Site-2: (a) total DOS of Sr3-xBixTi2O7 (x = 0.1667), (b) DOS of Ti, (c) DOS of O, (d) DOS of Bi.

Table 4 DOS at Fermi level and the energy difference of Fermi level compared with the undoped Sr3Ti2O7 for each concentration at both doping sites. The value of the Fermi level goes into the conduction band

	DOS at the Fermi level (electrons/eV)		The value of the Fermi level going into the conduction band (eV)
Sr_3-_xBi_xTi₂O₇	Site-1	Site-2	Site-1	Site-2
0.0278	1.3304	1.3471	0.2298	0.2015
0.0556	1.7589	1.4887	0.3472	0.3371
0.1667	11.2738	4.8282	0.5631	0.4555

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First-Principles Study on the Stability and Electronic Properties of Bi-Doped Sr₃Ti₂O₇

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