钛酸锶钡(Ba_1-xSr_xTiO₃, BST)铁电材料因具有良好的介电、铁电与压电性能，在动态存储器、可调谐微波器与雷达移相器等领域有着广泛的应用前景。随着通信系统与微电子技术的快速发展，BST已不能满足高性能微波调谐器件的设计需求，而掺杂是改善其性能的重要手段之一。本文采用第一性原理方法计算分析了K、Sn单掺与K-Sn共掺BST(60/40)电子结构与光学性质的微观掺杂改性规律，并通过实验研究了掺杂系列陶瓷的微观结构、介电与铁电性能以及掺杂系列薄膜的射频磁控溅射制备工艺、晶体结构、表面形貌与铁电性能。本文选取的K掺杂比例为5%，8%，10%，12.5%；Sn掺杂比例为5%，10%，15%，20%；K-Sn共掺杂比例为5%，10%。主要研究结论如下：

        (1)电子结构与光学性质计算结果表明，BST(60/40)为间接带隙半导体，带隙值为1.706eV，Ti的3d与O的2p轨道之间的强杂化作用是其产生铁电性的主要原因。对于掺杂体系，K⁺取代A位的Ba²⁺与Sr²⁺，Sn⁴⁺取代B位的Ti⁴⁺。与BST(60/40)相比，K掺杂后体系的晶格常数a减小，Sn掺杂与K-Sn共掺后体系的晶格常数a增大，其带隙值均增大。态密度与差分电荷密度结果表明，体系中Ba-O、Sr-O与K-O以离子键形式存在，Ti-O与Sn-O以共价键形式存在。对比复介电函数实部结果可知，K-Sn共掺弥补了单一掺杂的不足，K-Sn掺入后体系的静态介电常数值由K、Sn单掺的11.7和6.12增大至59.89。K-Sn共掺后增强了体系在0eV～2eV的光跃迁特性与光存储效率，同时提高了体系在15eV～20eV的光透过率。

(2)掺杂BST(60/40)系列陶瓷的晶体结构结果表明，所有样品均为四方相钙钛矿结构，且(110)衍射峰的偏移情况与理论计算晶格常数a的变化相一致。表面形貌结果表明，K掺杂能够细化晶粒，Sn掺杂有利于晶粒生长。而K-Sn共掺存在大小晶粒相互填充现象，样品致密度提高。在室温下，测试频率1kHz时，K、Sn单掺与共掺样品中的12.5%K、5%Sn与10%K-Sn掺杂样品的相对介电常数最大，分别为2357、1174与1085。在100kHz处K-Sn共掺杂样品的综合介电性能最优，其介电常数增大的同时，降低了介电损耗。在20kV/cm测试电场下，所有样品均具有铁电性，与BST(60/40)相比，掺杂陶瓷的剩余极化强度与矫顽场强均增大。

(3)通过射频磁控溅射法制备掺杂BST(60/40)系列薄膜的工艺研究，得到最佳溅射参数如下：衬底温度为500℃，溅射氧氩比为20:20，溅射气压为1Pa，溅射功率为100W，溅射时间为3h，原位退火时间为30min，退火氧氩比为20:20。晶体结构与表面形貌测试结果表明，BST(60/40)为单晶结构薄膜，掺杂薄膜样品均为多晶钙钛矿结构，均沿(111)晶面择优生长，薄膜表面平整光滑，结晶性良好，且各膜层结合良好，界面清晰。与BST(60/40)样品相比，K掺杂薄膜晶格常数减小，Sn掺杂薄膜晶格常数增大，K-Sn共掺杂薄膜晶格常数先减小后增大，与理论计算晶格常数a的变化情况相符合。薄膜的电滞回线形状与饱和度良好，均表现出铁电性，与BST(60/40)薄膜相比，K、Sn掺杂薄膜的剩余极化强度有所提高。

本文通过理论计算与实验相结合的方法，对比分析了K、Sn单掺与共掺BST(60/40)的微观掺杂改性规律。该研究能够为BST(60/40)铁电材料的掺杂研究提供理论指导与实验基础，有望制备出高性能的BST(60/40)基材料，并广泛应用于微波调谐器件等领域。

Barium Strontium Titanate (Ba_1-xSr_xTiO₃, BST) ferroelectric material is widely applied in dynamic memory, tunable microwaves and radar phase shifters due to its excellent dielectric, ferroelectric and piezoelectric properties. With the rapid development of communication system and microelectronics technology, BST material cannot meet the design requirements of high performance microwave tuning devices, and doping is one of the most important means to enhance the performance of BST. In this paper, the electronic structure and optical properties of K, Sn single doped and K-Sn co-doped BST(60/40) are calculated by the first principle method, and the microscopic modification mechanism is analyzed. The microstructure, dielectric and ferroelectric properties of doped BST(60/40) ceramics are studied through experiments. And the RF magnetron sputtering fabrication process, crystal structure, surface morphology and ferroelectric properties of doped BST(60/40) thin films are studied. The doping ratios are 5%, 8%, 10%, 12.5% for K, 5%, 10%, 15%, 20% for Sn, and 5%, 10% for K-Sn. The main conclusions are summarized as follows:

         (1)The calculation results of electronic structure and optical properties show that BST(60/40) is an indirect bandgap semiconductor with the bandgap of 1.706 eV. The strong hybridization between Ti 3d and O 2p orbitals is the origin of its ferroelectricity. For the doping system, K⁺ replaces Ba²⁺ and Sr²⁺ at the A site, and Sn⁴⁺ replaces Ti⁴⁺ at the B site. Compared with BST(60/40), the lattice constant a decreases after K doping, and increases after Sn doping and K-Sn co-doping, and the band gap is enlarged. The results of density of states and differential charge density show that Ba-O, Sr-O and K-O exist as ionic bonds, Ti-O and Sn-O exist as covalent bonds. The results of complex dielectric function real part show that K-Sn co-doping makes up the deficiency of single doping, and the static dielectric constant increases from 11.70 and 6.12 with K and Sn single doping to 59.89 with K-Sn co-doping. As well as, K-Sn co-doping improves the optical transition properties and storage efficiency between 0eV and 2eV, and the optical transmittance is enhanced between 15eV and 20eV.

        (2)The crystal structure results of doped BST(60/40) ceramics show that all the samples are tetragonal perovskite structure, and the shift of (110) diffraction peak is consistent with the theoretical calculation of the lattice constant a. The surface morphology results show that K doping can refine grains, and Sn doping is conducive to the growth of grains. The grain of K-Sn co-doping can fill with each other, which improves the density of samples. Among the K, Sn single doped and co-doped samples, the relative dielectric constants under 1kHz of the 12.5%K, 5%Sn and 10%K-Sn doped samples are the largest at room temperature, which are 2357, 1174 and 1085, respectively. The comprehensive dielectric properties of K-Sn samples are the best at 100kHz, because of the decrease of dielectric loss and the increase of dielectric constant. With the field of 20kV/cm, all the samples present ferroelectricity. Compared with BST(60/40) samples, the residual polarization and coercive field strength of the doped samples are enhanced.

        (3)The optimal RF magnetron sputtering parameters of doped BST(60/40) film fabrication are studied as follows: substrate temperature of 500℃, sputtering oxygen-argon ratio of 20:20, sputtering pressure of 1Pa, sputtering power of 100W, sputtering time of 3h, annealing time of 30min, annealing temperature of 500℃, and the annealing atmosphere of oxygen-argon ratio of 20:20. The XRD results show that BST(60/40) film exhibit single crystal structure, and the doped films are polycrystalline perovskite structure. All of the films preferentially grew along the (111) plane, and the surface of films is smooth with good crystallinity. The layers are well combined and the interface is clear. Compared with BST(60/40) samples, the lattice constant a of K-doped films decreases, Sn-doped films increases, and K-Sn co-doped films decreases firstly and then increases, which are in good accordance with the theoretical results. The hysteresis loop shape and saturation of the films are good, and they all exhibit ferroelectric properties. Compared with BST(60/40), the residual polarization strength of K and Sn doped films is improved.

In this paper, the combination and comparative analysis of theoretical calculation and experiment are used to explain the micro modification mechanism of K, Sn single doped and co-doped BST(60/40). This research can provide theoretical guidance and experimental basis for the doping research of BST(60/40) ferroelectric materials, and is expected to fabricate high performance BST(60/40)-based materials, which can be widely applied in microwave tuning devices and other fields.