The structure, polarization characteristics and underlying mechanism in KNaNbO (KNN50) are studied using first-principles calculations and neutron total scattering. We thoroughly examined the stability of rhombohedral (), orthorhombic () and tetragonal () phases with various K/Na configurations, among which phase is indeed energy favored, which could account for local monoclinic () polarization around [110] in KNN50. Significant distortions towards [111] occurs due to K/Na radii difference and Nb ferroelectric instability, which ultimately contributes to the enhanced piezoelectricity. To be noted, rather than inducing polarization itself as Li in KNbO-LiNbO, Na plays auxiliary role in KNN50 - it enhances Nb polarization, and bonding with one of surrounding O atoms stabilizes the phase. Moreover, the phase could indeed be misalignment of phases, further contributing to the local structure fluctuation and piezoelectric enhancement. These findings are valuable for further design and enhancement of (K,Na)NbO-based ferroelectrics.

中文翻译：

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Na 在原型无铅 K0.5Na0.5NbO3 压电材料结构和极化特性中的作用

利用第一性原理计算和中子全散射研究了 KNaNbO (KNN50) 的结构、极化特性和潜在机制。我们彻底研究了具有各种 K/Na 配置的菱形 ()、斜方 () 和四方 () 相的稳定性，其中相确实是能量有利的，这可以解释 KNN50 中 [110] 附近的局部单斜 () 极化。由于 K/Na 半径差异和 Nb 铁电不稳定性，导致 [111] 发生显着畸变，这最终有助于增强压电性。值得注意的是，Na 在 KNN50 中起着辅助作用，而不是像 KNbO-LiNbO 中的 Li 那样诱导极化本身 - 它增强了 Nb 极化，并且与周围 O 原子之一的键合稳定了相。此外，相位确实可能是相位未对准，进一步导致局部结构波动和压电增强。这些发现对于进一步设计和增强 (K,Na)NbO 基铁电体具有重要价值。