铌酸钾钠((K_0.5Na_0.5)NbO₃，KNN)基压电材料是一种高性能环境友好型无铅压电功能材料，具有高压电性能、高机电耦合系数以及高居里温度等优点，不仅广泛应用于传统微机电器件、超声换能器、调谐器等领域，还在人工智能、生物医疗、智慧家居和MEMS等科技前沿领域具有广阔的应用前景。本文通过第一性原理理论计算与固相烧结法实验相结合，主旨对Li、Zr掺杂KNN机理及调控作用进行了研究。计算了Li、Zr掺杂KNN能带、态密度、光学介电压电与铁电性质，实验测试了XRD、SEM、拉曼、阻抗和介电压电铁电性能。

首先，对Li单掺KNN机理与调控研究，Li单掺杂比例x分别为0.02、0.04、0.06、0.08和0.1，化学式记为(K_0.5Na_0.5)_1-xLi_xNbO₃。旨在以Li掺杂离子半径减小为例，系统研究Li单掺KNN电子结构、相结构、形貌结构、畴行为和氧空位行为对KNN介电压电和铁电性能的影响。引入的Li离子半径小于K和Na的离子半径影响了Nb-O八面体畸变程度，进而增大能带带隙值，增强Nb-O的p-d轨道杂化作用；Li的引入还使KNN从正交相转变为四方相，在0.06Li掺杂时存在正交相-四方相的MPB。理论计算与实验测试的介电性能、压电性能和铁电性能趋势吻合，且都有好的表现，第一性原理计算中静态介电常数为5.98，压电常数达到57.3pC/N，铁电自发极化为30μC/cm²，实验测试介电常数为480，压电常数达到194pC/N，饱和极化值为13.16μC/cm²。

然后，对Zr单掺KNN机理与调控研究，Zr单掺杂比例y分别为0.01、0.02、0.04、0.06和0.08，化学式记为(K_0.5Na_0.5)Nb_1-yZr_yO₃。旨在以Zr⁴⁺掺杂，其离子价态对比Nb⁵⁺更低为例，引入晶格后会形成电子空穴，电子浓度降低，费米面容易向价带移动导致能带增大，直接增强了B-O原子共价作用，增强p-d轨道杂化作用。由于理论计算未考虑到氧空位影响，Zr引入会增强体系的介电性能、压电性能和铁电性能；在实验角度由于氧八面体中B-O作用，从而导致介电性能增大；固相烧结实验中，Zr掺杂后KNN从正交相转变为对称性更高的伪立方相，晶粒尺寸值也下降至1μm以下，实际晶体畸变程度最小，压电性能在Li、Zr掺杂中最弱；说明由Zr低价掺杂进入体系，引入氧空位补偿电荷，引入的氧空位与晶界处ZrO₂共同抑制畴的转向，即钉扎了畴的运动，使得介电损耗和铁电矫顽场增大。

其次对Li-Zr共掺KNN机理与调控进行了研究，在Li掺杂x为0.06时，Zr共掺比例y分别为0.01、0.02、0.04、0.06和0.08，化学式记为(K_0.5Na_0.5)_0.94Li_0.06Nb_1-yZr_yO₃，旨在探究Li-Zr共掺杂对KNN性能影响的共同调控机理。理论计算中Li-Zr共掺对能带带隙值增大程度最大，这是由于Li离子半径更小与Zr低价掺杂共同导致；Li主要对5-20eV范围内态密度起到贡献作用，而Zr主要增强了对-5-0eV和2-10eV的态密度贡献，在介电性能计算中发现其最大程度上加强了体系的介电性能；固相烧结的Li-Zr共掺KNN陶瓷中，KNN从正交相转变为四方相再转变为伪立方相，其压电性能也展现出减小趋势；Li-Zr共掺晶粒尺寸迅速减小至1μm，与Zr单掺相似，但Li掺杂使陶瓷更加致密；Li的挥发与Zr低价掺杂的共同作用使氧空位量达到最大，但是0.06Li的存在减小了电滞回线展宽的程度，使得KNN还保留了一部分铁电体的特征。实验中发现Li-Zr共掺KNN介电压电和铁电性能弱于Li单掺KNN，强于Zr单掺KNN，体现了Li和Zr共掺对体系介电压电和铁电性能的共同调控作用。

最后，对高压下相结构和电子结构对KNN体系光学性质和压电性能影响微观机理进行了研究。随着外加压力从0增加至21GPa，KNN晶胞内晶格常数减小（原子间距离减小），电子结构中的能带带隙先减小后增大，电子结构电子云重叠程度增大和原子间静电作用增强。在外加压力15-18GPa范围内，KNN从三方相R相转变为正交相O相，此时R相和O相自由能差值低，自由能分布更平坦，晶格在外场下更容易发生形变，NbO₆^-八面体也更容易发生畸变从而增强KNN压电性能。对比不同压力下计算得到的KNN晶体的介电性能和压电性能，在外加压力为15GPa下的KNN具有优良的介电性能和最大的压电性能e₃₃=7.2C/m²，即在相转变压力点附近NbO₆^-八面体发生畸变导致晶体整体的电偶极矩增加时的KNN具有最优的介电性能与压电性能。

Potassium sodium niobate-based ((K_0.5Na_0.5)NbO₃, KNN) piezoelectric material is a high-performance and environmentally friendly lead-free piezoelectric functional material. It has the advantages of high piezoelectric properties, electromechanical coupling coefficient and high Curie temperature. It is not only widely used in traditional MEMS devices, ultrasonic transducers, tuners and other fields, but also has broad application prospects in the frontier fields of artificial intelligence, biomedicine, smart home and MEMS. In this paper, the mechanism and regulation of Li and Zr doped KNN were studied by combining first-principles theoretical calculation with solid-phase sintering method. The band structure, density of states, optical dielectric-voltage and ferroelectric properties of Li, Zr doping KNN were calculated. XRD, SEM, Raman, impedance and dielectric-voltage ferroelectric properties were tested.

Firstly, the mechanism and regulation of Li single doped KNN were studied. The Li doping ratio x was 0.02, 0.04, 0.06, 0.08 and 0.1, respectively, and the chemical formula was (K_0.5Na_0.5)_1-xLi_xNbO₃. The purpose of this study is to systematically study the effects of Li-doped KNN electronic structure, phase structure, morphology, domain behavior and oxygen vacancy behavior on the dielectric-voltage and ferroelectric properties of KNN. The introduction of Li ion radius smaller than K and Na makes the KNN system cell be stretched, which affects the degree of Nb and Zr-O octahedron distortion, thereby increasing the band gap value and enhancing the p-d orbital hybridization of Nb-O. The introduction of Li also transforms KNN from orthorhombic phase to tetragonal phase. There is an orthorhombic-tetragonal phase MPB when 0.06 Li is doped. The two mechanisms are enhanced and regulated together to make the theoretical calculation consistent with the experimental test of the dielectric-voltage and ferroelectric properties, and both have good performance. In the first-principles calculation, the static dielectric constant is 5.98, the piezoelectric performance reaches 5.73pC/N, and the ferroelectric spontaneous polarization is 30μC/cm².In the experimental test, the dielectric constant is 480, the piezoelectric performance reaches 194pC/N, and the saturation polarization is 13.16μC/cm².

Then the mechanism and regulation of Zr doping KNN were studied. The Zr single doping ratio y was 0.01,0.02,0.04,0.06 and 0.08, and the chemical formula was (K_0.5Na_0.5)Nb_1-yZr_yO₃. The purpose is to take Zr⁴⁺ doping, whose ion valence state is lower than Nb⁵⁺ as an example. The introduction of lattice will form electric holes, the electron concentration will be reduced, the Fermi surface is easy to move to the valence band, resulting in an increase in the energy band, which directly enhances the covalent effect of B-O atoms and enhances the p-d orbital hybridization. Because the theoretical calculation does not take into account the influence of oxygen vacancies, the introduction of  Zr will enhance the dielectric voltage and ferroelectric properties of the system. At the experimental angle, the B-O effect in the oxygen octahedron leads to an increase in dielectric properties; in the solid phase sintering experiment, the KNN changed from the orthorhombic phase to the pseudo-cubic phase with higher symmetry after Zr doping, and the grain size also decreased to less than 1μm. The actual crystal distortion was the smallest, and the piezoelectric properties were the weakest in Li and Zr doping. It is indicated that the oxygen vacancies are introduced to compensate the charge by the low-valence doping of Zr into the system. The introduced oxygen vacancies and ZrO₂ at the grain boundary jointly inhibit the domain steering, that is, pinning the domain motion behavior, making the dielectric loss and ferroelectric coercive field increase.

Secondly, the mechanism and regulation of Li-Zr co-doping KNN were studied. When Li doping x is 0.06, the Zr co-doping ratio y is 0.01,0.02,0.04,0.06 and 0.08, respectively, and the chemical formula is (K_0.5Na_0.5)_0.94Li_0.06Nb_1-yZr_yO₃, aiming to explore the common regulation mechanism of Li-Zr co-doping on KNN performance. In the theoretical calculation, Li-Zr co-doping has the greatest increase in the band gap value, which is due to the smaller radius of Li ions and the low valence doping of Zr. Li mainly contributes to the density of states in the range of 5-20eV, while Zr mainly enhances the contribution to the density of states of-5-0eV and 2-10eV. In the calculation of dielectric properties, it is found that the dielectric properties of the system are enhanced to the greatest extent. The KNN in the solid-phase sintered ceramic-based Li-Zr co-doped KNN changes from the orthogonal phase to the tetragonal phase and then to the pseudo-cubic phase, and its piezoelectric properties also show a decreasing trend. It is found that the grain size of Li-Zr co-doped ceramics decreases rapidly to 1μm, which is similar to that of Zr single-doped ceramics, but the presence of Li makes the ceramics denser. Starting from the oxygen vacancy mechanism, the volatilization of Li and the introduction of Zr low-valence doping jointly maximize the amount of oxygen vacancies, but the presence of 0.06Li reduces the degree of hysteresis loop broadening, so that KNN also retains some ferroelectric characteristics. In the experiment, it is found that the dielectric voltage and ferroelectric properties of Li-Zr co-doped KNN are weaker than those of Li single-doped KNN and stronger than those of Zr Single doped KNN, which reflects the common regulation of Li and Zr co-doping on the dielectric voltage and ferroelectric properties of the system.

Finally, the microscopic mechanism of KNN system under high pressure was studied by theoretical calculation. The influence mechanism of different pressures on the piezoelectric properties of KNN is systematically studied and the optimal pressure working point of KNN was determined. The results show that as the applied pressure increases from 0 to 21 GPa, the lattice constant of the KNN crystal cell( the distance between atoms) decreases, the band gap in the electronic structure decreases first and then increases, the overlap of the electronic structure electron cloud increases and the electrostatic interaction between atoms increases. In the range of 15-18 GPa, KNN transforms from rhombohedral  phase to orthorhombic phase. At this time, the free energy difference between R phase and O phase is low, the free energy distribution is more flat, the lattice is more prone to deformation under the external field, and NbO₆^-octahedron is also more prone to distortion to enhance KNN piezoelectric properties. Comparing the dielectric properties and piezoelectric properties of KNN crystals calculated under different pressures, A comparative study of dielectric properties and piezoelectric properties of KNN crystals under different pressures reveals that KNN has excellent dielectric properties and maximum piezoelectric properties e₃₃=7.2C/m² at the applied pressure of 15GPa. When the distortion of NbO₆^-octahedron leads to the increase of the overall electric dipole moment of the crystal, KNN show the best dielectric properties and piezoelectric properties nearing the phase transition pressure point.