Structure and electrical properties of [(Na_0.825K_0.175)_0.5Bi_0.5]_1+xTiO₃piezoceramics with A-site nonstoichiometry

Abstract

A type of nonstoichiometric piezoceramics, [(Na 0.825 K 0.175 ) 0.5 Bi 0.5 ] 1+x TiO 3 (BKNT-x, x = 0-0.009), was synthesized by the conventional sintering method. The effects of Bi 3+ , Na + and K + content on the structure and electrical properties of 0.825Bi 0.5 Na 0.5 TiO 3 -0.175Bi 0.5 K 0.5 TiO 3 piezoceramics were investigated.The XRD patterns demonstrated that BKNT-x piezoceramics form a solid solution without a secondary phase. Meanwhile, SEM micrographs indicated that excess [(Na 0.825 K 0.175 ) 0.5 Bi 0.5 ] 2+ suppresses grain growth and that BKNT-x ceramics become considerably denser. BKNT-0.002 ceramics offer the following enhanced properties: d 33 = 154 pC/N, k p = 33%, ε r = 1087, tanδ = 0.036, and Q m = 116. This improvement of properties is most likely related to the dense structure and the maintenance of morphotropic phase boundaries through the introduction of a proper A-site cation excess. For ceramics containing volatile elements, stoichiometric control is an efficacious method of enhancing performance.

Piezoelectric and Dielectric Properties in Bi0.5(Na,K)0.5TiO3-x Ag2O Lead-Free Piezoceramics

“…Currently, research on BNT-based ceramics primarily focuses on enhancing their performance through replacement and doping strategies. For instance, studies have been conducted on BNT-BaTiO 3 [10,11], Bi 0.5 (Na 1−x−y Li y K x ) 0.5 TiO 3 [12], Bi 0.5 Na 0.5 TiO 3 -K 0.5 Bi 0.5 TiO 3 (BNKT) [13], Bi 0.5 Na 0.5 TiO 3 -KNbO 3 [14], Bi 0.5 Na 0.5 TiO 3 -BaTiO 3 -KNbO 3 [15], [(K 0.175 Na 0.825 ) 0.5 Bi 0.5 ] 1+x TiO 3 [16],…”

Enhanced electric field-induced strain and electrostrictive response of lead-free BaTiO3-modified Bi0.5(Na0.80K0.20)0.5TiO3 piezoelectric ceramics

“…The Bi 3+ ion has 6s 2 lone pair electrons similarly to Pb 2+ ion, which can cause high ferroelectricity and good polarizability; so the BNT ceramic has attracted extensive attention [1]. The pure BNT ceramic has a typical perovskite structure with rhombohedral phase at ambient temperature and possesses a large remnant polarization (P r ~ 32 μC/cm 2 ) and high Curie temperature (T c ~ 320 °C) [3,[8][9][10]. However, the BNT ceramic has many drawbacks, such as: (1) it has a large coercive field (E c ) and high electrical conductivity, so it is easy to broken down during the polarization, (2) Na and Bi easily volatilize at high temperatures (HT), resulted to reduce the density of the material, and (3) BNT ceramic cannot satisfy the actual application of capacitors due to the dielectric constant (ε r ) at room temperature (RT) is only ~ 800 [5].…”