Study on the Effects of (Bi_1/2Na_1/2)TiO₃ Content on the Curie Temperature of (Bi_1/2Na_1/2)TiO₃-BaTiO₃ PTCR Ceramics

Abstract:

Perovskite-structured (Bi_1/2Na_1/2)TiO₃ (BNT) ferroelectric with Curie temperature about 320°C is considered to be a good candidate of high temperature lead-free materials with a positive temperature coefficient of resistance (PTCR). In this study, lead-free PTCR ceramics with compositions of (1-x)BaTiO₃-x(Bi_1/2Na_1/2)TiO₃ (BT-BNT x=0.5-55mol%) were successfully prepared without any additional donor or acceptor dopants. The effects of BNT content on the Curie temperature T_c and the PTC effect of the ceramic materials were investigated. The X-ray diffraction data indicated that BT phase and BNT phase formed a solid solution during sintering even though the x value was up to 55mol%. The Curie temperature T_c of the samples increased from ~130°C to ~216°C with the increase of the BNT amount (x value) from 0.5mol% to 40mol%. However, it decreased when excess BNT was added (x value increased from 40mol% up to 55mol%), which was resulted from the volatile effects of Bi³⁺ and Na⁺ ions during sintering. The sample of 0.6BaTiO₃- 0.4(Bi_1/2Na_1/2)TiO₃ with T_c =216°C, room-temperature resistivity 10⁴ Ω·cm and R_max/R_min= 10^2.7 was obtained. There is a relationship between the Curie temperature and the cell volume of the perovskite structured lattice.

• Periodical: Materials Science Forum (Volume 687)
• Pages: 411-415
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.687.411
• Online since: June 2011
• Authors: Long Xing Yang, Xing Wen Zhu, Li Zhe Li, Wen Zhong Jiang, Xiao Zhou
• Keywords: BNT, Cell Volume, Lead-Free, Positive Temperature Coefficient PTC, Volatilization

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