Effect of Sr Doping on Electrical Transport and Emission of 12CaO·7Al2O3 Electride

doi:10.15541/jim20180326

Abstract

Abstract:

[Ca₂₄Al₂₈O₆₄] ⁴⁺:4e ^-(C12A7:e ^-) is a new cathode material with low working temperature and low work function, and its unique cage structure attracts attention of researchers. In this work, the Sr doped (C_1-_xS_x)12A7:e ^-(0≤x≤0.05) were prepared by high temperature solid phase reaction combined with spark plasma sintering (SPS), and the electron compound (Ca_1-_xSr_x)12A7:e ^- was successfully obtained by reduction of Ti particles at 1100 ℃ for 20 h. The first principle calculations for electronic structure show that Sr doping changes the band structure of C12A7:e ^-, the Framework Conduction Band (FCB) decreases to 0.3 eV, benefits the electrical properties of (Ca_1-_xSr_x)12A7:e ^-. The total density of states (DOS) of (Ca_1-_xSr_x)12A7:e ^-near the Fermi energy level is increased. The electrical transport characteristics test results show that the (Ca_0.96Sr_0.04)12A7:e ^- has the highest conductivity 1136 S/cm and carrier concentration (2.13±0.11)×10 ²¹ cm ^-3, indicating that Sr doping is benefical for reducing the preparation time of mayenite electride. The thermionic emission performance test results show that Sr doping significantly increases the emission current density and effectively reduces the average effective work function. The (Ca_0.96Sr_0.04)12A7:e ^- has the best emission performance, and the emission current density reaches 1.45 A/cm ² at 1100 ℃ and a anode voltage of 3500 V. The Zero field emission current density is 0.74 A/cm ², and the Richardson work function reduces from 2.01 eV (un-doped) to 1.86 eV.

Key words: C12A7:e ^-electride, Sr doping, electrical transport, emission performance

CLC Number:

TQ174

Wei-Kang ZHAO, Xin ZHANG, Qi FENG, Ji-Ping ZHAO, Hong-Liang LIU, Fan LI, Yi-Xin XIAO, Yan-Qin LIU, Jiu-Xing ZHANG. Effect of Sr Doping on Electrical Transport and Emission of 12CaO·7Al₂O₃ Electride[J]. Journal of Inorganic Materials, 2019, 34(5): 521-528.

Figures/Tables 9

Fig. 1 Schematic structure of (a) a unit cell of C12A7, (b) a single- cage structure of C12A7 with free O2-, (c) single Sr-doped cage

Fig. 2 (a) Electronic band structure for C12A7:e- and (Ca1-xSrx)12A7:e-, and (b) schematic energy structures of C12A7:e- and (Ca1-xSrx)12A7:e-

Fig. 4 Partial density of states (PDOS) of (Ca1-xSrx)12A7:e-

Fig. 3 Total density of states (TDOS) of (Ca1-xSrx)12A7:e-

Fig. 5 (A) XRD patterns and (B) local magnification XRD patterns of (Ca1-xSrx)12A7(0≤x≤0.05) polycrystalline powders Insets in (A): Pictures of (Ca1-xSrx)12A7(0≤x≤0.05) polycrystalline bulk before (a) and after (b) Ti reduction; (c) Lattice constants of (Ca1-xSrx)12A7:e-

Fig. 6 Cross-sectional SEM images of (Ca1-xSrx)12A7:e- (0≤ x≤0.05)

Table 1 Electrical conductivity σ, electron concentration Ne, and electron mobility μH at room temperature (RT) of different samples

Sr-doped samples	σ/(S?cm^-1)	N_e/(×10²¹ cm^-3)	μ_H/(cm²?V^-1?S^-1)
x=0	142	0.06	1.51
x=0.01	354	0.86	2.62
x=0.02	892	1.82	3.08
x=0.03	917	2.04	3.43
x=0.04 (20 h, 1100 ℃)	1136	2.13	3.75
x=0.05	25	—	—
Sample*^[23] (48 h, 1100 ℃)	1165	2.40	3.00

Fig. 7 Calculate J0 of (Ca1-xSrx) 12A7:e- polycrystalline by method of Schottky

Fig. 8 Thermionic emission current of the (Ca1-xSrx) 12A7:e- polycrystalline

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Effect of Sr Doping on Electrical Transport and Emission of 12CaO·7Al₂O₃ Electride

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