Yokoi T, Yoshiya M, Yasuda H
Department of Adaptive Machine Systems, Osaka University , 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Langmuir. 2014 Dec 2;30(47):14179-88. doi: 10.1021/la503338x. Epub 2014 Nov 18.
The energetically favorable spatial configuration of M(3+) ions and oxide-ion vacancies near a symmetrical grain boundary (GB) in cubic zirconia is determined for various trivalent species M(3+) (M = Al, Sc, Y, Gd, La), and the driving force for grain boundary segregation (GBS) quantitatively examined using atomistic Monte Carlo simulations in conjunction with static lattice calculations. For a high concentration of ∼10 mol %, it is found that point defects near a GB plane preferentially occupy specific sites to minimize total lattice energy, rather than being randomly distributed. Systematic analysis shows that energetically stable configurations of segregants vary depending on their ionic radii. Analysis of the driving force for GBS as a function of dopant concentration reveals that three important factors govern GBS. First, occupation of specific sites by point defects is necessary to minimize the total lattice energy; enrichment of point defects near the GB plane with random configuration does not decrease the total lattice energy significantly because of strong Coulombic interactions. Second, the factors governing GBS change with increasing dopant concentration. At dilute concentrations, relief of bond strain is the dominant factor, while at high concentrations Coulombic interactions, which depend strongly on the specific arrangement of defects, become another dominant factor. Third, the stabilization of matrix cations, Zr(4+) ions, is the dominant factor to lower the driving force for GBS at all concentrations. In contrast, the stabilization of M(3+) ions does not necessarily contribute to GBS of point defects at high concentrations. These findings suggest practical ways to control GBS to enhance materials' properties or minimize detrimental effects.
针对立方氧化锆中对称晶界（GB）附近M(3+)离子和氧离子空位的能量有利空间构型，研究了各种三价物种M(3+)（M = Al、Sc、Y、Gd、La），并结合静态晶格计算，使用原子蒙特卡罗模拟定量研究了晶界偏析（GBS）的驱动力。对于约10 mol%的高浓度，发现GB平面附近的点缺陷优先占据特定位置以最小化总晶格能量，而不是随机分布。系统分析表明，偏析剂的能量稳定构型因其离子半径而异。对GBS驱动力随掺杂剂浓度变化的分析表明，有三个重要因素控制GBS。首先，点缺陷占据特定位置对于最小化总晶格能量是必要的；随机构型的GB平面附近点缺陷的富集不会显著降低总晶格能量，因为存在强库仑相互作用。其次，控制GBS的因素随掺杂剂浓度增加而变化。在低浓度时，键应变的缓解是主导因素，而在高浓度时，强烈依赖于缺陷特定排列的库仑相互作用成为另一个主导因素。第三，基质阳离子Zr(4+)离子的稳定化是在所有浓度下降低GBS驱动力的主导因素。相比之下，M(3+)离子的稳定化在高浓度时不一定有助于点缺陷的GBS。这些发现提出了控制GBS以增强材料性能或最小化有害影响的实用方法。
