Ge-doping in TiO2-Nb2O5-CaCO3 Varistor Ceramics: Structure and Property

doi:10.15541/jim20170237

Abstract

Abstract:

TiO₂ varistors are typical electronic devices with nonlinear current-voltage property fabricated from TiO₂ ceramics. This study investigated the influence of Ge doping on the nonlinear coefficient α and the breakdown electric field E_B of TiO₂-Nb₂O₅-CaCO₃ varistor ceramics. TiO₂-Nb₂O₅-CaCO₃ varistor ceramics doped with Ge were successfully prepared by using traditional method of ball milling-molding-sintering. The electrical performance, including nonlinear coefficient α, breakdown electric field E_B, and leakage current J_L, was tested with a varistor-direct current-parameter instrument. Average barrier height Φ_B of each sample was calculated by relevant formula. Analysis of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning transmission electronic microscopy demonstrated that Ge doping notably changed the microstructure of TiO₂-Nb₂O₅-CaCO₃ ceramics, thereby increasing α and decreasing E_B. When Nb₂O₅ and CaCO₃ doping content were 0.5mol%, the TiO₂-Nb₂O₅-CaCO₃ varistor ceramics doping with 1.0 mol% Ge exhibited high α (10.6), low E_B (8.7 V/mm), and highest Φ_B (1.73 eV), superior to previous published findings. Furthermore, Ge with low melting point as sintering aid could reduce the sintering temperature of the varistor ceramics, with optimal sintering temperature at 1300℃.

Key words: TiO₂varistor, nonlinear coefficient, breakdown voltage, Ge

CLC Number:

TP204

KANG Kun-Yong, XU Kai-Meng, LIU Can, YANG Xiao-Qing, ZHENG Zhi-Feng. Ge-doping in TiO₂-Nb₂O₅-CaCO₃ Varistor Ceramics: Structure and Property[J]. Journal of Inorganic Materials, 2018, 33(4): 447-452.

Figures/Tables 10

References 25

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Sample	Doping content/mol%
Sample	TiO₂	Nb₂O₅	CaCO₃	Ge
#1	99.0	0.5	0.5	0
#2	98.8	0.5	0.5	0.2
#3	98.6	0.5	0.5	0.4
#4	98.4	0.5	0.5	0.6
#5	98.2	0.5	0.5	0.8
#6	98.0	0.5	0.5	1.0
#7	97.8	0.5	0.5	1.2
#8	97.6	0.5	0.5	1.4

Sample	Doping content/mol%
Sample	TiO₂	Nb₂O₅	CaCO₃	Ge
#1	99.0	0.5	0.5	0
#2	98.8	0.5	0.5	0.2
#3	98.6	0.5	0.5	0.4
#4	98.4	0.5	0.5	0.6
#5	98.2	0.5	0.5	0.8
#6	98.0	0.5	0.5	1.0
#7	97.8	0.5	0.5	1.2
#8	97.6	0.5	0.5	1.4

Sample	1200℃		1250℃		1300℃		1350℃		1400℃
Sample	α	E_B	α	E_B	α	E_B	α	E_B	α	E_B
#1	—	—	—	—	4.8	28.7	5.8	24.5	6.6	23.7
#2	—	—	4.1	25.2	5.2	23.6	5.1	23.2	4.9	24.5
#3	3.7	28.9	4.7	24.0	6.3	20.5	6.2	21.5	6.1	21.3
#4	4.5	27.4	6.2	21.4	8.4	16.8	8.2	16.4	8.0	16.8
#5	5.4	26.8	6.9	20.1	9.1	12.4	8.9	12.1	8.5	12.7
#6	7.1	26.2	8.5	19.5	10.6	8.7	9.7	8.4	9.3	9.2
#7	6.7	25.4	8.1	18.3	9.2	8.3	8.6	7.6	7.8	8.0
#8	6.2	23.5	7.6	15.6	8.5	7.2	8.0	7.2	7.1	7.5

Sample	1200℃		1250℃		1300℃		1350℃		1400℃
Sample	α	E_B	α	E_B	α	E_B	α	E_B	α	E_B
#1	—	—	—	—	4.8	28.7	5.8	24.5	6.6	23.7
#2	—	—	4.1	25.2	5.2	23.6	5.1	23.2	4.9	24.5
#3	3.7	28.9	4.7	24.0	6.3	20.5	6.2	21.5	6.1	21.3
#4	4.5	27.4	6.2	21.4	8.4	16.8	8.2	16.4	8.0	16.8
#5	5.4	26.8	6.9	20.1	9.1	12.4	8.9	12.1	8.5	12.7
#6	7.1	26.2	8.5	19.5	10.6	8.7	9.7	8.4	9.3	9.2
#7	6.7	25.4	8.1	18.3	9.2	8.3	8.6	7.6	7.8	8.0
#8	6.2	23.5	7.6	15.6	8.5	7.2	8.0	7.2	7.1	7.5

Sample	D_g/μm	ρ_r	α	E_B/(V·mm^-1)	J_L/(μA·cm^-2)	Φ_B/eV
#1	1.05	93.5	4.8	28.7	12.7	0.63
#2	1.46	94.3	5.2	23.6	11.8	0.87
#3	1.92	95.1	6.3	20.5	11.2	1.05
#4	2.48	95.8	8.4	16.8	10.5	1.36
#5	2.83	96.8	9.1	12.4	9.8	1.56
#6	3.15	97.2	10.6	8.7	9.2	1.73
#7	3.75	97.8	9.2	8.3	8.9	1.51
#8	4.12	98.5	8.5	7.2	8.5	1.42

Ge-doping in TiO₂-Nb₂O₅-CaCO₃ Varistor Ceramics: Structure and Property

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Position	Element/at%
	O K		Ti K		Nb K		Ca K		Ge K
	#1	#6	#1	#6	#1	#6	#1	#6	#1	#6
1	74.35	73.40	23.25	23.41	0.12	0.09	2.28	2.89	-	0.21
2	73.43	70.48	24.61	25.46	0.20	0.15	1.76	3.75	-	0.16
3	73.64	69.41	25. 48	28.50	0.67	0.69	0.21	0.08	-	1.32
4	77.55	76.12	21.63	21.73	0.55	0.48	0.27	0. 16	-	1.51

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