Nominal Lanthanum Niobate, a Versatile Additive for Reducing Grain Boundary Resistance in Conductive Ceramics

Abstract

Conductive ceramics currently play a vital role in human life. In practical applications, most conductive ceramics are polycrystalline, and their overall conductivity (σtotal) is influenced by both bulk and grain boundary resistances (Rbulk and Rgb, respectively). While Rbulk is mainly of academic interest, Rgb often determines the quality of a conductive ceramic component. Currently, studies discussing the influence of specific methods on grain boundary resistances are typically related to individual ceramics. In this study, it is discovered that the addition of 0.5–3 mol% nominal LaNbO4 significantly reduces the Rgb of several well-known conductive ceramics, such as rhombohedral NaSICON-type Na+-ion-conducting Na3.4Zr2Si2.4P0.6O12 and Li+-ion conducting Li1.5Al0.5Ti1.5P3O12, Li+-ion-conducting tetragonal perovskite Li0.34La0.56TiO3, oxygen-ion-conducting cubic fluorite 8 mol% Y2O3 stabilized ZrO2, and electron-conducting perovskite SrTiO3 (sintered in a reducing atmosphere). In particular, for NZSP and LATP, the enhanced σtotal reaches 9.3 × 10−3 S cm−1 and 2.1 × 10−3 S cm−1 at 25 °C, surpassing previously published results. Detailed investigations reveal that the microstructure of the grain boundaries in all the ceramics undergoes significant improvements. The findings elevate the importance of research on grain boundaries, inspiring the development of conductive ceramics with higher σtotal for superior applications.