题名: | (Mg1-xZnx)2SiO4低介微波介质陶瓷的低温烧结与改性 |
作者: | |
学号: | 19211025009 |
保密级别: | 保密(4年后开放) |
语种: | chi |
学科代码: | 080502 |
学科: | 工学 - 材料科学与工程 - 材料学 |
学生类型: | 硕士 |
学位: | 工学硕士 |
学位年度: | 2022 |
学校: | 西安科技大学 |
院系: | |
专业: | |
研究方向: | 功能陶瓷 |
导师姓名: | |
导师单位: | |
提交日期: | 2022-06-16 |
答辩日期: | 2022-06-01 |
外文题名: | Low temperature sintering and modification of (Mg1-xZnx)2SiO4 low dielectric microwave dielectric ceramics |
关键词: | 微波介质陶瓷 ; (Mg1-xZnx)2SiO4 ; 溶胶凝胶-熔盐法 ; 第一性原理计算 |
外文关键词: | Microwave dielectric ceramics ; (Mg1-xZnx)2SiO4 ; Sol-gel molten salt method ; The first-principle calculation |
摘要: |
新型毫米波器件和5G通信系统对低介微波介质陶瓷的性能提出了更高的要求,(Mg1-xZnx)2SiO4陶瓷具有低εr,高Q×f及成本低等特点,但烧结温度过高且τf值往往偏负较大,因此开发研究低温烧结高性能的(Mg1-xZnx)2SiO4微波介质陶瓷对推进毫米波通讯及基板材料的发展具有重要的科学意义和应用价值。 本文采用固相法制备了(Mg1-xZnx)2SiO4陶瓷,研究了不同配比及不同成型方式时陶瓷的介电性能,确定该实验条件下最佳的Mg/Zn比。通过溶胶凝胶法和溶胶凝胶-熔盐法合成高反应活性的纳米粉体,对比两种工艺获取最优粉体的参数,结合热压成型制备优良介电性能的(Mg1-xZnx)2SiO4陶瓷。以期通过掺杂CuO降低(Mg1-xZnx)2SiO4陶瓷的烧结温度,复合CaTiO3调节陶瓷的谐振频率温度系数。最后基于第一性原理计算Mg2SiO4和(Mg1-xZnx)2SiO4的Mulliken布局分析和弹性常数等结构和物理性质,分析对比Zn取代后对Mg2SiO4结构的影响,并对之前的一些实验结果进行了理论验证。主要结论如下: (1) 研究了不同组分配比对(Mg1-xZnx)2SiO4陶瓷介电性能的影响,结果表明当x = 0.2时样品的结构以Forsterite为主晶相,当x > 0.4时转变为以Willemite为主晶相。1325 oC下干压成型和热压成型得到的(Mg0.4Zn0.6)2SiO4陶瓷的性能参数分别为ρ = 3.53 g/cm3,εr = 6.74,tanδ = 8.88×10-4和ρ = 3.96 g/cm3,εr = 6.36,tanδ = 1.35×10-3。热压成型得到的(Mg1-xZnx)2SiO4陶瓷相较于干压成型的试样,其体积密度整体增大,εr和tanδ在论文实验条件下变化范围分别为6.16 ~ 7.57和1.10×10-3 ~ 2.66×10-3,展现了在不同组分和工艺条件下更稳定的性能。 (2) 通过溶胶凝胶法结合热压成型可使(Mg0.4Zn0.6)2SiO4陶瓷的烧结温度从1375 oC降至1225 oC,与固相烧结法对比,体积密度明显增大,有效降低了MZS陶瓷烧结温度,但也增大了陶瓷的介电损耗。通过溶胶凝胶-熔盐法以ZnCl2-KCl为熔盐制备的同一组分陶瓷,在同一烧结温度下其介电常数和介电损耗均有改善。 (3) 通过CuO掺杂可有效降低干压成型(Mg0.4Zn0.6)2SiO4陶瓷的烧结温度,同时进一步提升陶瓷的介电性能,掺杂0.5 wt % CuO的陶瓷样品于1225 oC下烧结4 h后的ρ = 3.50 g/cm3,介电性能最优为εr = 6.54,tanδ = 8.85×10-4。热压成型时1225 oC下1 wt % CuO掺杂的(Mg0.4Zn0.6)2SiO4陶瓷微波介电性能为εr = 6.49,Q×f = 2982 GHz,τf = -47.17 ppm/°C。研究了CaTiO3对(Mg0.4Zn0.6)2SiO4陶瓷烧结和性能的影响,发现其不仅可以有效调制谐振频率温度系数,同时可降低烧结温度。1175 °C下烧结的90 wt % (Mg0.4Zn0.6)2SiO4-10 wt % CaTiO3陶瓷和1200 °C下烧结的85 wt % (Mg0.4Zn0.6)2SiO4-15 wt % CaTiO3陶瓷的谐振频率温度系数分别为-1.39 ppm/°C和1.75 ppm/°C,已平衡至0 ppm/°C左右。1175 oC下95 wt % (Mg0.4Zn0.6)2SiO4-5 wt % CaTiO3陶瓷的低频介电性能和微波介电性能相对较好,其介电性能参数分别为εr = 7.35,tanδ = 8.97×10-4和εr = 8.79,Q×f = 8959 GHz,τf = -17.95 ppm/°C。 (4) 通过第一性原理计算得Mg2SiO4和(Mg0.4Zn0.6)2SiO4的禁带宽度分别为4.588 eV和2.771 eV。(Mg0.4Zn0.6)2SiO4费米能级附近的主要贡献为O2p和Zn3d轨道,表明Zn-O键为共价键。Zn-O键贡献了晶胞中大部分的共价键,削减了结构中离子极化作用,导致(Mg0.4Zn0.6)2SiO4的介电常数相比于Mg2SiO4降低了约10 %。Mg2SiO4具有弹性稳定性,Zn原子的取代会使其失去弹性稳定性,增大体积模量、剪切模量和泊松比,从而使陶瓷的τf值趋近零值。 |
外文摘要: |
New millimeter wave devices and 5G communication systems put forward higher requirements for the performance of low dielectric microwave dielectric ceramics, (Mg1-xZnx)2SiO4 ceramics have low εr, high Q×f and low cost, but the sintering temperature is too high and the value of τf is too negative. Therefore, the development and research of low-temperature sintered high-performance (Mg1-xZnx)2SiO4 microwave dielectric ceramics has important scientific significance and application value for promoting the development of millimeter wave communication and substrate materials. In this paper, (Mg1-xZnx)2SiO4 ceramics were prepared by the solid-phase sintering method. The dielectric properties of ceramics with different ratios and different molding methods were studied, and the optimal Mg/Zn ratio was determined under the experimental conditions. High reactive nano powders were synthesized by sol-gel method and sol-gel molten salt method. Comparing the two processes to obtain the optimal powder parameters, combined with hot pressing to prepare (Mg1-xZnx)2SiO4 ceramics with excellent dielectric properties. It is expected that the sintering temperature of (Mg1-xZnx)2SiO4 ceramics can be reduced by doping CuO, and the resonant frequency temperature coefficient of ceramics can be adjusted by composite CaTiO3. Finally, the Mulliken layout analysis, elastic constant and other electronic structures and physical properties of Mg2SiO4 and (Mg1-xZnx)2SiO4 are calculated based on the first principle. The effects of Zn substitution on the structure of Mg2SiO4 are analyzed and compared, and some previous experimental results are verified theoretically. The main conclusions are as follows: (1) The effect of different composition ratios on the dielectric properties of (Mg1-xZnx)2SiO4 ceramics was studied. The results showed that Forsterite is the main crystal phase when x = 0.2, and Willemite is the main crystal phase when x > 0.4. The performance parameters of (Mg0.4Zn0.6)2SiO4 ceramics formed by dry pressing and hot pressing at 1325 oC are ρ = 3.53 g/cm3, εr = 6.74, tanδ = 8.88×10-4 and ρ = 3.96 g/cm3, εr = 6.36, tanδ = 1.35×10-3. The bulk density of (Mg1-xZnx)2SiO4 ceramics obtained by hot pressing is higher than that of dry pressing, εr and tanδ under the experimental conditions, the variation range are 6.16 ~ 7.57 and 1.10×10-3~ 2.66×10-3, showing more stable performance under different components and process conditions. (2) The sintering temperature of (Mg0.4Zn0.6)2SiO4 ceramics decreased from 1375 oC to 1225 oC by sol-gel method combined with hot pressing. Compared with the solid-phase sintering method, bulk density increased significantly, and the sintering temperature of MZS ceramics was effectively reduced, but the dielectric loss of ceramics was also increased. The same component ceramics prepared by sol-gel molten salt method using ZnCl2-KCl as molten salt, the dielectric constant and dielectric loss of ceramics were optimized at the same sintering temperature. (3) CuO doping can effectively reduce the sintering temperature of dry pressed (Mg0.4Zn0.6)2SiO4 ceramics and further improve the dielectric properties of ceramics. The ceramic samples doped with 0.5 wt % CuO were sintered at 1225 oC for 4 h ρ = 3.50 g/cm3, the best dielectric properties are εr = 6.54, tanδ = 8.85×10-4. The microwave dielectric properties of 1 wt % CuO doped (Mg0.4Zn0.6)2SiO4 ceramics at 1225 oC during hot pressing are εr = 6.49, Q×f = 2982 GHz, τf = -47.17 ppm/°C. The effect of CaTiO3 on the sintering and properties of (Mg0.4Zn0.6)2SiO4 ceramics was studied. It was found that CaTiO3 can not only effectively modulate the temperature coefficient of resonant frequency, but also reduce the sintering temperature. The resonant frequency temperature coefficients of 90 wt % (Mg0.4Zn0.6)2SiO4-10 wt % CaTiO3 ceramics sintered at 1175 °C and 85 wt % (Mg0.4Zn0.6)2SiO4-15 wt % CaTiO3 ceramics sintered at 1200 oC are -1.39 ppm/°C and 1.75 ppm/°C respectively, which have been balanced to about 0 ppm/°C. The low-frequency dielectric properties and microwave dielectric properties of 95 wt % (Mg0.4Zn0.6)2SiO4-5 wt % CaTiO3 ceramics at 1175 °C are relatively good, and their performance parameters are ρ = 3.70 g/cm3, εr = 7.35, tanδ = 8.97×10-4 and εr = 8.79, Q×f = 8959 GHz, τf = -17.95 ppm/°C. (4) The band gap widths of Mg2SiO4 and (Mg0.4Zn0.6)2SiO4 calculated by the first principle are 4.588 eV and 2.771 eV respectively. The main contributions near the Fermi level of (Mg0.4Zn0.6)2SiO4 are O2p and Zn3d orbitals, indicating that the Zn-O bond is covalent. The Zn-O bond contributes most of the covalent bonds in the crystal cell and reduces the ion polarization in the structure, resulting in a decrease of about 10 % in the dielectric constant of (Mg0.4Zn0.6)2SiO4 compared with Mg2SiO4. Mg2SiO4 has elastic stability. The substitution of Zn atoms make it lose its elastic stability, increase the bulk modulus, shear modulus and Poisson ratio, and make the τf value of ceramics approaches zero. |
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中图分类号: | TQ174.1 |
开放日期: | 2026-06-15 |