Synergistic Enhancement of Anti-Reduction Performance and Dielectric Stability in Lu-Doped BaTiO3 Ceramics via Grain Boundary Segregation

To meet the requirements of next-generation base metal electrode multilayer ceramic capacitors (BME-MLCCs) for low cost, high integration, and high stability, this work investigates the regulatory effects of rare-earth Lu 3+ doping on the microstructure, reduction resistance, and dielectric properties of BaTiO 3 -based ceramics sintered under a reducing atmosphere. A series of BaTiO 3 - x Lu ( x = 0, 2, 3, 4) ceramics were prepared via the conventional solid-state route and sintered in a reducing atmosphere (0.5% H 2 /N 2 ). The results demonstrate two distinct roles of Lu 3+ doping. First, Lu 3+ incorporation at the B-site (substituting for Ti 4+ ) introduces lattice microstrain, which stabilizes the pseudocubic phase. Second, the enrichment of Lu 3+ at grain boundaries induces a solute-drag effect that kinetically suppresses grain-boundary migration, thereby confining the average grain size to 100-150 nm. The coupled effects of the cubic phase and nanoscale grains contribute to performance enhancement in three key aspects: first, the increased energy barrier for charge-carrier migration and the space-charge layer at grain boundaries effectively suppress oxygen vacancy and electronic conduction, leading to a high resistivity on the order of 10 11 Ω·cm under reducing conditions; second, the nanoscale pseudocubic grains exhibit relaxor-like behavior, which broadens the permittivity peak and enables compliance with the X7R temperature stability specification (for x =3, ε r = 1535, tanδ = 0.0079 at room temperature); finally, the nanograins promote the formation of polar nanoregions, substantially improving DC-bias stability (with a permittivity variation of only 3.87% under 0-2 V/μm). This study elucidates the mechanism by which Lu 3+ , through grain boundary segregation, synergistically refines grains, stabilizes the cubic phase, and optimizes electrical performance, offering an effective material strategy for developing fine-grained cubic-phase BaTiO 3 dielectrics for high-performance BME-MLCCs.