摘 要

微波介质陶瓷，是指应用于微波频段（主要是UHF、SHF频段）电路中作为介质材料并完成一种或多种功能的陶瓷，在现代通信中被广泛用作谐振器、滤波器、介质基片、介质天线、介质导波回路等。随着移动通信技术向更小型化和更高频化的发展，微波介质陶瓷的低温烧结、低损耗以及介电常数可调、微波器件的进一步实用化成为新一轮研究的热点。本论文以固相法路线探索制备钛酸镁基微波介质陶瓷的工艺，通过添加Li₂CO₃改善其烧结性能和介电性能，得到如下主要研究结果：

1. 以(MgCO₃)₄·Mg(OH)₂·5H₂O和TiO₂为原料，通过干法球磨，在1100℃保温3h预烧，用PVA溶液造粒，干压成型，烧结等步骤，采用固相法成功制备了MgTiO₃陶瓷。谐振频率f₀=9.05GHz时，ε_r=13.03，tan δ=5.40×10^-4。
2. Li₂CO₃添加量在x(Li)lt;0.03和x(Li) gt; 0.05时有利于降低烧结温度，但x(Li) gt; 0.15后，虽然有利于降低烧结温度，但对烧结后的样品致密化程度损害较大。
3. 碳酸锂掺杂后的钛酸镁基陶瓷，在微观结构中可以观察到孔隙，大颗粒的尺寸在12~15 µm左右，小颗粒的尺寸在2~5 µm左右，晶粒表面可以观察到条纹。
4. Li₂CO₃添加量在x(Li)lt;0.15时有利于提高钛酸镁基微波介质陶瓷的介电性能，在x(Li)值在0.5~0.10间有最佳性能。在该范围内，烧结温度先升高后降低，且x=0.05的烧结温度1400℃大于x=0.10的烧结温度1350℃；在该范围内，介电常数先升高后降低，且x=0.05的介电常数ε_r=15.36略大于x=0.10的介电常数ε_r=15.28，介电损耗先降低后升高，且x=0.05的介电损耗tan δ=2.77×10^-4略小于x=0.10的介电损耗3.33×10^-4。
5. 确定的最佳成分组成和烧成工艺参数为：(Mg_0.90,Li_0.10)TiO₃，原料在1100℃预烧3h，预烧后的粉末造粒成型后，升温至800℃保温1h以充分排除粘结剂，之后升温至1350℃烧结2h，升温速率在温度小于1100℃时为5℃/min，大于1100℃时为3℃/min。x=0.10，谐振频率f₀=8.09GHz时，ε_r=15.28，tan δ=3.33×10^-4。

本论文首次对(Mg_1-x,Li_x)TiO₃体系的微波介质性能作了初步研究，所得结果对Li₂CO₃改善钛酸镁基陶瓷的烧结性能和介电性能具有一定的指导作用。

关键词：微波介质陶瓷；MgTiO₃；Li₂CO₃；介电性能

Abstract

Microwave dielectric ceramics, which are defined as the ceramics used in microwave circuits (UHF, SHF) as dielectric materials to performing one or more functions, are widely used as resonators, filters, dielectric substrate tablets, media antenna, dielectric waveguide circuit and other areas in modern telecommunication. As mobile communication technology developmental tend of miniaturization and higher frequency, new hot spots of research have appeared such as low-temperature sintering of microwave dielectric ceramics, low dielectric loss with the adjustable dielectric constant and more practical microwave devices. In this paper, magnesium titanate based microwave dielectric ceramic materials were prepared by solid-state reaction method, improved by adding Li₂CO₃ in sintering properties and dielectric properties. Main results of the research were obtained:

1. MgTiO₃ ceramic materials were prepared by solid-state reaction method using (MgCO₃)₄·Mg(OH)₂·5H₂O and TiO₂ as raw materials. The preparation process comprised: dry ball milling, calcination at 1100 ℃ for 3 h, granulating with PVA solution, dry-pressed forming and sintering. The dielectric property was obtained of f₀ = 9.05GHz, ε_r = 13.03，tan δ = 5.40×10^-4.
2. The amount of additive of Li₂CO₃ was that x(Li) is lower than 0.03 or higher than 0.05, which is helpful to reduce the sintering temperature. However, Li₂CO₃ may damage the densification of ceramic badly when x(Li) is higher than 0.15.
3. Magnesium titanate based ceramics doped with lithium carbonate was observed porosity in the microstructure. The size of the large grains is of about 12 ~ 15μm while the size of small grains is of about 2 ~ 5μm. The stripes were observed on the surface of the grains.
4. The amount of additive of Li₂CO₃ was that x(Li) is lower than 0.15,which is helpful to improve the dielectric properties of the magnesium titanate based microwave dielectric ceramics. The optimal dielectric properties was obtained of x(Li) values ​​of 0.5 ~ 0.10. In this range, the sintering temperature first increased then decreased, and the sintering temperature of 1400 ℃ and x value of 0.05 was higher than that of 1350 ℃ and x value of 0.10. The dielectric constant first increased then decreased, and the dielectric constant of 15.36 and x value of 0.05 was slightly larger than that of 15.28 and x value of 0.10. The dielectric loss first decreased then increased, and the dielectric loss of 2.77 × 10^-4 and x value of 0.05 is slightly smaller than that of 3.33 × 10^-4 and x value of 0.10.
5. The optimal component composition and process of preparation was (Mg_0.90,Li_0.10) TiO₃. The raw material was calcined at 1100 ℃ for 3 h then granulated. The powders were pressed homogeneously into pellets and the pellets were calcined at 800 ℃ for 1h to exclude the binder, then sintered at 1350 ℃ for 2h at a heating rate of 5 ℃/min when the temperature was lower than 1100 ℃ and 3 ℃/min when that was higher than 1100 ℃. The optimal property was obtained of x = 0.10, f₀ = 8.09GHz, ε_r = 15.28, tan δ = 3.33×10^-4.

In this paper, the microwave dielectric properties of the (Mg_1-x,Li_x)TiO₃ system was researched preliminarily for the first time. The results of the research is a significant guidance for using Li₂CO₃ to improve the sintering properties and the dielectric properties of magnesium titanate based ceramics.

Key Words: microwave dielectric ceramics; MgTiO₃; Li₂CO₃; dielectric properties

目录

第1章 绪论 1

1.1 微波介质陶瓷 1

1.1.1 微波介质陶瓷的特征及应用 1

1.1.2 微波介质陶瓷的发展趋势 1

1.2 钛酸镁基陶瓷简述 1