Sr掺杂对12CaO·7Al2O3电子化合物电输运及发射性能的影响

doi:10.15541/jim20180326

无机材料学报 ›› 2019, Vol. 34 ›› Issue (5): 521-528.DOI: 10.15541/jim20180326

Sr掺杂对12CaO·7Al₂O₃电子化合物电输运及发射性能的影响

赵伟康¹,张忻¹(),冯琦¹,赵吉平¹,刘洪亮¹,李凡¹,肖怡新¹,刘燕琴¹,张久兴^1,²

^1. 北京工业大学材料科学与工程学院, 新型功能材料教育部重点实验室, 北京 100124
^2. 合肥工业大学材料科学与工程学院, 合肥 230009

收稿日期:2018-07-16 修回日期:2018-09-20 出版日期:2019-05-20 网络出版日期:2019-05-14
作者简介:赵伟康(1992-), 男, 硕士研究生. E-mail:zhaoweikang@emails.bjut.edu.cn
基金资助:
国家自然科学基金(51371010);国家自然科学基金(51572066);国家自然科学基金(50801002);北京市自然科学基金(2112007)

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

Wei-Kang ZHAO¹,Xin ZHANG¹(),Qi FENG¹,Ji-Ping ZHAO¹,Hong-Liang LIU¹,Fan LI¹,Yi-Xin XIAO¹,Yan-Qin LIU¹,Jiu-Xing ZHANG^1,²

^1. Key Laboratory of Advanced Functional Materials, Ministry of Education, College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China
^2. School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China

Received:2018-07-16 Revised:2018-09-20 Published:2019-05-20 Online:2019-05-14
Supported by:
National Natursal Science Foundation of China(51371010);National Natural Science Foundation of China(51572066);National Natural Science Foundation of China(50801002);National Natural Science Foundation of Beijing(2112007)

摘要/Abstract

摘要：

12CaO·7Al₂O₃电子化合物(C12A7:e ^-)是一种具有低工作温度和低逸出功等优点的新型电子化合物阴极材料。通过高温固相反应结合放电等离子烧结制备Sr掺杂(Ca_1-_xSr_x)12A7 (0≤x≤0.05)块体, 并在1100 ℃采用Ti颗粒还原20 h成功制得电子化合物(Ca_1-_xSr_x)12A7:e ^-。第一性原理计算结果表明, (Ca_1-_xSr_x)12A7:e ^-与C12A7:e ^-相比, 框架导带下移, 费米能级附近态密度增加, 这将有利于电输运和发射性能的优化。室温电输运测试结果表明, Sr掺杂有利于C12A7:e ^-电输运性能的优化, 其中(Ca_0.96Sr_0.04)12A7:e ^-样品在室温下具有最高电导率(1136 S/cm)以及最高载流子浓度(2.13×10 ²¹ cm ^-3), 与相同条件下制备的C12A7:e ^-样品相比, 载流子浓度提高近2个数量级, 表明Sr掺杂可以有效缩短制备C12A7:e ^-的制备时间。热电子发射性能测试结果表明, 随着Sr掺杂量的增加, 热电子发射性能逐渐提高, 其中(Ca_0.96Sr_0.04)12A7:e ^-样品具有最佳的热发射性能, 在1100 ℃外加电压3500 V时, 发射电流密度达到1.45 A/cm ², 零场发射电流密度达到0.74 A/cm ², 理查生逸出功降低至1.86 eV。

关键词: 12CaO·7Al₂O₃电子化合物, Sr掺杂, 电输运, 发射性能

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

中图分类号:

TQ174

赵伟康, 张忻, 冯琦, 赵吉平, 刘洪亮, 李凡, 肖怡新, 刘燕琴, 张久兴. Sr掺杂对12CaO·7Al₂O₃电子化合物电输运及发射性能的影响[J]. 无机材料学报, 2019, 34(5): 521-528.

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.

图/表 9

图1 (a) C12A7:e-晶体, (b) C12A7:e-单个笼腔和(c) Sr掺杂C12A7:e-单个笼腔结构示意图

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

图2 (a)C12A7:e-和(Ca1-xSrx)12A7:e-的能带结构; (b)C12A7:e-和(Ca1-xSrx)12A7:e-的能带结构示意图

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-

图4 (Ca1-xSrx)12A7:e-各原子分态密度

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

图3 (Ca1-xSrx)12A7:e-的总体态密度

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

图5 (Ca1-xSrx)12A7(0 ≤ x≤0.05)粉末的XRD图谱(A)和局部放大XRD图谱(B)

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-

图6 (Ca1-xSrx)12A7:e-的断面SEM照片(0≤x≤0.05) (a) x=0; (b) x=0.01; (c) x=0.02; (d) x=0.03; (e) x=0.04; (f) x=0.05

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

表1 (C1-xSx)12A7:e-系列样品在室温下的电导率、电子浓度和迁移率

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

图7 肖特基外延法计算(Ca1-xSrx) 12A7:e-样品零场发射电流密度 (a) x=0; (b) x=0.01; (c) x=0.02; (d) x=0.03; (e) x=0.04

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

图8 (Ca1-xSrx) 12A7:e-样品的发射电流密度

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

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Sr掺杂对12CaO·7Al₂O₃电子化合物电输运及发射性能的影响

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

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