Observation of La3+ entering (Bi2O2)2+ layer to tune tilting of NbO6 octahedra in CaBi2Nb2O9 ceramics

Abstract

Bismuth-layered CaBi2Nb2O9 (CBN) ceramics hold great potential for the development of high-temperature vibration sensors applicable in harsh environment application scenarios such as aerospace and power plants. While chemical doping in the pseudo-perovskite blocks has generally improved the piezoresponse of CBN ceramics, limited research has focused on tuning the (Bi2O2)2+ layer, and there is a lack of direct evidence regarding dopant incorporation in this layer. Here, we present evidence using employing spherical aberration corrected scanning transmission electron microscopy (STEM) and Raman spectroscopy to demonstrate successful La3+ dopant incorporation into Bi3+ sites within the (Bi2O2)2+ layer, thereby tuning the tilting of the NbO6 octahedra. Furthermore, the La3+/W6+ doping strategy leads to a significant enhancement of both the piezoelectric coefficient (d33) and electrical resistivity (ρ) in CBN ceramics. The La3+/W6+ co-doped CaBi2-xLaxNb2-xWxO9 ceramics exhibited optimal performance (d33 = 15.9 pC/N, ρ = 5.4 × 105 Ω cm@600 °C, TC = 918 °C) near pseudo-tetragonal phase boundary (at x = 0.025). Importantly, the d33 of CaBi1.975La0.025Nb1.975W0.025O9 ceramics only degraded by 8.8% after annealing at 900 °C, rendering excellent thermal stability for harsh environment applications. This study highlights substituting Bi3+ with La3+ in (Bi2O2)2+ layers as an important alternative approach for enhancing both piezoelectric properties and high temperature resistivity in Aurivillius ceramics, deviating from the traditional focus on tailoring pseudo-perovskite blocks as previously explored.