Segregation‐controlled densification and grain growth in rare earth‐doped Y2O3
Segregation‐controlled densification and grain growth in rare earth‐doped Y2O3
复制标题
稀土掺杂 Y2O3 中的偏析控制致密化和晶粒生长
DOI：
10.1111/jace.17907
复制
发表时间：
2021
影响因子：
3.9
通讯作者：
Olivier Guillon
中科院分区：
文献类型：
--
作者：
Moritz Kindelmann;Ke Ran;Wolfgang Rheinheimer;Koji Morita;Joachim Mayer;Martin Bram;Olivier Guillon
Y2O3 的阳离子掺杂是在烧结过程中调整致密化和晶粒生长的既定方法。然而，掺杂阳离子在晶界的偏析及其对加工的影响仍未完全了解。由于电荷与主晶格不匹配而导致的静电效应或由离子尺寸不匹配引起的弹性效应可以驱动偏析。虽然偏析是由热力学引起的，但它会影响致密化和微观结构演化过程中的扩散和晶界动力学。在本研究中，我们使用两种等价掺杂剂（La3+和Gd3+），即我们关注偏析的弹性成分。我们研究了场辅助烧结/火花等离子体烧结 (FAST/SPS) 期间掺杂和未掺杂 Y2O3 的致密化以及晶粒生长动力学。虽然 Gd3+ 对致密化没有显着影响，但 La3+ 导致烧结活性大大降低。此外，对烧结过程中和预致密化样品的晶粒生长行为的分析表明，晶粒生长系数有所下降，其中 La3+ 的影响最强。通过像差校正 TEM 观察晶界的结构和化学性质。虽然掺杂没有引起结构变化，但化学分析显示 La3+ 向晶界强烈偏析，而 Gd3+ 则观察不到这种情况。结果表明，偏析的 La3+ 通过溶质拖拽导致晶界迁移速率急剧下降，并且烧结动力学慢得多，这可能是由于偏析导致晶界自扩散减少所致。这项研究进一步强调了弹性对阳离子偏析的重要性，并建立了与晶粒生长和烧结动力学的明确关系，这两者都会因偏析而降低。
Cation doping of Y2O3is an established approach for tailoring densification and grain growth during sintering. However, the segregation of doped cations to the grain boundary and their impact on processing are still not completely understood. Segregation can be driven by electrostatic effects due to charge mismatch with the host lattice or elastic effects induced by ion size mismatch. While segregation is caused by thermodynamics, it impacts diffusion and the kinetics of grain boundaries during densification and microstructure evolution. In this study, we utilize two isovalent dopants (La3+and Gd3+), that is we focus on the elastic component of segregation. We investigate the densification as well as the grain growth kinetics of both doped and undoped Y2O3during field‐assisted sintering/spark plasma sintering (FAST/SPS). While Gd3+is showing no significant effect on densification, La3+resulted in a strongly reduced sintering activity. Furthermore, the analysis of the grain growth behavior during sintering and on predensified samples revealed a decrease in the grain growth coefficient, with La3+having the strongest impact. The structure and chemistry at the grain boundary were observed by aberration‐corrected TEM. While no structural change was caused by doping, the chemical analysis showed a strong segregation of La3+to the grain boundary, which could not be observed for Gd3+. The results indicate that segregated La3+causes a drastic decrease in grain boundary migration rates through solute drag as well as much slower sintering kinetics, likely caused by a decrease in the grain boundary self‐diffusion due to segregation. This study further underlines the importance of the elastic contribution to cation segregation and establishes a clear relationship to grain growth and sintering kinetics, which are both decreased by segregation.