铁电陶瓷材料钛酸锶钡(化学式为Ba_1-xSr_xTiO₃，简称BST)因其优良的铁电和介电属性，在动态存储器、微波调谐器和雷达相位调节器等领域显示出巨大应用潜力。不过，随着通信和微电子产业的快速发展，BST在满足高性能微波调谐设备需求方面存在局限，故通过掺杂技术改进BST的性质成了提高其工业应用能力的重要手段。在本项研究中，结合了第一性原理计算和实验上采用固相烧结法，对K和Sn元素掺杂BST系统的作用原理及调控效果进行了详细的研究分析。研究内容不限于对K和Sn掺杂BST的能带结构、电子态密度及介电特性的理论计算，还包括了利用X射线衍射(XRD)、扫描电子显微技术(SEM)、XPS(X射线光电子能谱)、拉曼光谱、阻抗特性分析以及对其介电与铁电性质的实验验证。

研究首先聚焦于K单掺杂BST的作用机制和调控效果，探究不同K掺杂比例x(0.05、0.08、0.10、0.125)下的(Ba_0.6Sr_0.4)_1-xK_xTiO₃样品。通过分析K掺杂所导致的离子半径缩小对BST电子结构、相变、形貌、畴结构及氧空位行为的影响，发现K⁺的引入导致BST晶格拉伸，影响Ti-O八面体的畸变，从而扩大了能带间隙并加强了Ti-O的p-d轨道混合作用。理论与实验结果在介电和铁电性能上均显示出良好的一致性，其中第一性原理计算得到的静态介电常数6.08，而实验测得的介电常数为2231.17。

在本研究中，对单独掺杂Sn的BST材料进行了深入分析，探究不同比例的Sn掺杂(比例为0.05、0.10、0.15、0.20)对Ba_0.6Sr_0.4Ti_(1-y)Sn_yO₃样品性能的影响。当Sn⁴⁺取代Ti⁴⁺进行掺杂时，作为等价掺杂，造成钙钛矿晶格中发生晶格畸变，促进电畴偏转，K掺杂使得费米面向价带方向移动，能带宽度随之增大，同时增强了B-O原子间的共价作用和p-d轨道的混合效应。实验结果表明，Sn掺杂使BST陶瓷晶粒尺寸先增加后减小，表明晶体畸变程度降至最低。这可能是因为Sn掺杂引入的氧空位补偿电荷，以及晶界处SnO₂的存在共同抑制了畴的转动，相当于在畴的运动上设置了“钉扎”，从而导致介电损耗和铁电矫顽场增加。这一系列研究揭示了Sn掺杂在调控BST铁电陶瓷性能中的复杂作用机制。

最后，本研究深入探讨了K-Sn共掺杂在BST体系中的调控效应，特别是在K掺杂比例x固定为0.05的前提 下，分析了不同Sn掺杂比例y(0.05、0.10、0.15、0.20)对(Ba_0.6Sr_0.4)_1-xK_xTi_(1-y)Sn_yO₃材料性能的影响。理论计算揭示，K和Sn共掺杂显著增加了能带宽度，这主要是由于K⁺半径缩小与Sn⁴⁺等价态掺杂的双重作用。在态密度方面，K、sn的贡献集中在-20-0 eV的能量范围内，从而在介电性能上实现了显著的增强。在实验层面，采用固相烧结法制备的K-Sn共掺杂BST陶瓷样品展现K、Sn掺杂作用还导致晶粒尺寸显著缩小至3μm，表明Sn掺杂使得BST陶瓷更密度。从氧空位机制的角度分析，K元素的挥发与Sn掺杂共同作用，最大化了氧空位的生成，而0.05的K掺杂量有效减小了电滞回线的展宽，从而保留了BST的部分铁电性质。综合实验结果表明，K-Sn共掺BST的介电与铁电性能虽不及单独掺K的BST，但优于单独掺Sn的BST，这体现了K和Sn共掺杂在调节材料介电及铁电性能方面的复合效应。

This study investigates the microstructural modification patterns and experimental preparation of BST (60/40) ferroelectric materials with varying proportions of K and Sn, both singly and in combination. Employing first-principles calculations, we analyzed the crystallographic parameters, electronic structures, dielectric, and optical properties of these materials. Additionally, the microstructures, dielectric, and ferroelectric properties of ceramic target materials were studied. Samples of doped thin films were fabricated using the RF magnetron sputtering technique, and their microstructures and ferroelectric properties were characterized. Key findings of this study are presented as follows:

The research primarily focuses on the mechanism and regulatory effects of K doping in BST, examining samples with different K doping ratios x (0.05, 0.08, 0.10, 0.125) of (Ba_0.6Sr_0.4)_1-xK_xTiO₃. Analysis of the impact of the reduced ionic radius due to K doping on the electronic structure, phase transitions, morphology, domain structures, and oxygen vacancy behavior of BST revealed that the introduction of K⁺ causes lattice stretching and affects the distortion of the Ti-O octahedra, thereby widening the bandgap and enhancing the p-d orbital hybridization of Ti-O. Both theoretical and experimental results showed good consistency in dielectric and ferroelectric properties, with a theoretically calculated static dielectric constant of 6.08 and an experimentally measured dielectric constant of 2231.17.

In-depth analysis was conducted on BST materials singly doped with Sn, investigating the effects of different Sn doping ratios (0.05, 0.10, 0.15, 0.20) on the properties of Ba_0.6Sr_0.4Ti_(1-y)Sn_yO₃ samples. When Sn⁴⁺ replaces Ti⁴⁺, equivalent doping causes lattice distortions in the perovskite structure, promoting domain wall motion and enhancing the covalent interactions between B-O atoms and the p-d orbital hybridization. Experimental results indicated that Sn doping initially increases and then decreases the grain size of BST ceramics, suggesting minimized crystal distortions. This is likely due to the compensation charge from oxygen vacancies introduced by Sn doping and the presence of SnO₂ at grain boundaries, which suppress domain rotation, akin to "pinning" the domain motion, thereby increasing dielectric loss and coercive field in ferroelectric properties.

Finally, the study thoroughly explored the regulatory effects of combined K-Sn doping in the BST system, particularly analyzing the impact of different Sn doping ratios y (0.05, 0.10, 0.15, 0.20) on the properties of (Ba_0.6Sr_0.4)_1-xK_xTi_(1-y)Sn_yO₃ materials under a fixed K doping ratio x of 0.05. Theoretical calculations revealed that combined K and Sn doping significantly increased the bandgap width, primarily due to the dual effect of the reduced radius of K⁺ and equivalent state doping of Sn⁴⁺. In terms of state density, contributions from K and Sn were concentrated in the -20 to 0 eV energy range, significantly enhancing the dielectric properties. Experimentally, solid-state sintering produced K-Sn co-doped BST ceramic samples showing a significant reduction in grain size to 3μm, indicating higher density of BST ceramics due to Sn doping. From the perspective of oxygen vacancy mechanisms, the volatilization of  K in conjunction with Sn doping maximized the formation of oxygen vacancies, while a K doping level of 0.05 effectively minimized the hysteresis loop broadening, thereby preserving some of BST's ferroelectric properties. Comprehensive experimental results demonstrated that although the dielectric and ferroelectric properties of K-Sn co-doped BST were not as high as those of BST doped solely with K, they were superior to those of BST doped solely with Sn, reflecting the combined effect of K and Sn co-doping in adjusting the material's dielectric and ferroelectric properties.

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