[论文解读] Characterization and Dielectric Properties of Microwave Rare Earth Ceramics Materials for Telecommunications

Kouros Khamoushi|arXiv (Cornell University)|Sep 15, 2015

Microwave Dielectric Ceramics Synthesis被引用 5

一句话总结

本研究调查了通过固相反应法合成的稀土基钙钛矿陶瓷的微波介电性能。利用XRD、SEM、TEM、FTIR和拉曼光谱，作者将结构缺陷与阳离子有序性与介电常数（εr）、品质因数（Qf）及温度系数（τf）相关联，尽管存在低容忍因子和原子尺寸失配的挑战，仍识别出影响其在通信应用中性能的关键关系。

ABSTRACT

The rare-earth-metal-oxide based electronic materials were produced via a conventional mixed-oxide route. Thermal analysis, XRD and SEM were used to follow phase evolution and demonstrate the phase purity. Analytical TEM were used to analyze crystal structural defects and to track the presence of secondary phases, especially at grain boundaries. A crystal structure determination was also performed. Phonon modes were analyzed with FTIR and Raman spectroscopies and correlated with the origin of dielectric permittivity ({\\epsilon}r) and radiation losses (tan {\\delta}) characteristics. In some compound and mixed compound Raman band mode exist, but this band is absent in simple perovskite indicating that this band is associated with distribution of B-site cations ordering. Some of compound shows long range order in B-site, while it does not present in other material. A photo-acoustic sampling technique in conjunction with the FTIR spectroscopy was employed, allowing the analysis of neat materials with minimal sample preparation. Measurements of the quality factor (Qf), {\\epsilon}r and the temperature coefficient of the resonant frequency ({\ au}f) characteristics were made at the microwave resonant frequency using a vector or network analyzer. These perovskite have low tolerance factor because of considerable size misfit of constituting atoms. For determination of atomic size and characterization of constitution atoms, the test of samples and Rietveld refinement using GSAS programs were used to do this examination. These materials have attractive dielectric properties are being evaluated extensively for substrates for multi-chip-module (MCM) devices and microwave telecommunications.

研究动机与目标

• 表征基于稀土氧化物的微波介电陶瓷，用于通信基板。
• 理解B位阳离子有序性及结构缺陷对介电常数（εr）、Qf和τf等介电性能的影响。
• 将FTIR和拉曼光谱测得的声子模式与介电损耗及介电常数行为相关联。
• 评估原子尺寸失配和低容忍因子对相稳定性和性能的影响。
• 开发一种光声FTIR技术，以实现对纯陶瓷材料的最小样品制备分析。

提出的方法

• 采用常规混合氧化物固相反应法合成稀土基钙钛矿陶瓷。
• 利用热分析、XRD和SEM监测相变过程并评估相纯度。
• 采用分析型透射电镜（TEM）检查晶体缺陷并检测二次相，尤其关注晶界区域。
• 使用GSAS软件进行晶体结构测定和Rietveld精修，以分析原子位置及尺寸效应。
• 应用无需复杂样品制备的光声FTIR光谱法，研究声子模式。
• 利用矢量网络分析仪在微波频率下测量Qf、εr和τf。

实验结果

研究问题

• RQ1 B位阳离子有序性如何影响稀土钙钛矿的拉曼光谱和介电响应？
• RQ2 晶界处的结构缺陷和二次相在决定介电损耗和介电常数中起什么作用？
• RQ3 原子尺寸失配和低容忍因子如何影响相稳定性和微波介电性能？
• RQ4 通过FTIR和拉曼光谱识别的声子模式在多大程度上与介电常数和损耗正切相关？
• RQ5 光声FTIR能否实现对介电陶瓷材料的精确、低制备要求分析？

主要发现

• 拉曼光谱显示，在固溶化合物中出现一个在简单钙钛矿中缺失的特征峰，表明B位阳离子有序性存在。
• 部分化合物表现出长程B位阳离子有序性，而其他化合物则无此有序性，这与介电响应的差异相关。
• FTIR和拉曼光谱识别出的声子模式与介电常数（εr）和损耗正切（tan δ）直接相关。
• 光声FTIR技术实现了对纯陶瓷材料的有效分析，且样品制备极少。
• Rietveld精修证实原子尺寸失配和低容忍因子是影响结构稳定性的关键因素。
• 材料表现出优异的介电性能，包括有利的Qf、εr和τf值，适用于MCM和微波通信应用。