The influence of excess K2O on the electrical properties of (K,Na)1/2Bi1/2TiO3 ceramics

Li, Linhao; Li, Ming; Sinclair, Derek C.

Abstract

The solid solution (KxNa0.50-x)Bi0.50TiO3 (KNBT) between Na1/2Bi1/2TiO3 (NBT) and K1/2Bi1/2TiO3 (KBT) has been extensively researched as a candidate lead-free piezoelectric material because of its relatively high Curie temperature and good piezoelectric properties, especially near the morphotropic phase boundary (MPB) at x ~ 0.10 (20 mol% KBT). Here we show low levels of excess K2O in the starting compositions, i.e. (Ky+0.03Na0.50-y)Bi0.50TiO3.015 (y-series), can significantly change the conduction mechanism and electrical properties compared to a nominally stoichiometric KNBT series (KxNa0.50-x)Bi0.50TiO3 (x-series). Impedance Spectroscopy measurements reveal significantly higher bulk conductivity (σb) values for y ≥ 0.10 samples (activation energy, Ea, ≤ 0.95 eV) compared to the corresponding x-series samples which possess band-gap type electronic conduction (Ea ~ 1.26 to 1.85 eV). The largest difference in electrical properties occurs close to the MPB composition (20 mol% KBT) where y = 0.10 ceramics possess b (at 300 oC) that is 4 orders of magnitude higher than x = 0.10 and the oxide-ion transport number in the former is ~ 0.70 – 0.75 compared to < 0.05 in the latter (between 600 and 800 oC). The effect of excess K2O can be rationalised on the basis of the (K + Na):Bi ratio in the starting composition prior to ceramic processing. This demonstrates the electrical properties of KNBT to be sensitive to low levels of A-site nonstoichiometry and indicates excess K2O in KNBT starting compositions to compensate for volatilisation can lead to undesirable high dielectric loss and leakage currents at elevated temperatures.

Citation

Li, L., Li, M., & Sinclair, D. C. (in press). The influence of excess K2O on the electrical properties of (K,Na)1/2Bi1/2TiO3 ceramics. Applied Physics Letters, 112, https://doi.org/10.1063/1.5025275

• Journal Article Type: Article
• Acceptance Date: Apr 14, 2018
• Online Publication Date: May 2, 2018
• Deposit Date: Jul 31, 2018
• Publicly Available Date: Jul 31, 2018
• Journal: Applied Physics Letters
• Print ISSN: 0003-6951
• Electronic ISSN: 1077-3118
• Publisher: American Institute of Physics
• Peer Reviewed: Peer Reviewed
• Volume: 112
• DOI: https://doi.org/10.1063/1.5025275
• Public URL: https://nottingham-repository.worktribe.com/output/930372
• Publisher URL: https://aip.scitation.org/doi/10.1063/1.5025275