Dielectric Losses of Microwave Ceramics Based on Crystal Structure
Dielectric Losses of Microwave Ceramics Based on Crystal Structure
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DOI：
10.5772/intechopen.82483
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发表时间：
2018-12
期刊：
影响因子：
--
通讯作者：
H. Ohsato;J. Varghese;H. Jantunen
中科院分区：
文献类型：
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作者：
H. Ohsato;J. Varghese;H. Jantunen
到目前为止，许多微波介质材料已经被研究用于一系列的通信应用。在电介质中，三个主要的介电特性是品质因数(Q)、介电常数和谐振频率的温度系数。其中，最本质的介电性质是Q。更具体地说，Q是介质损耗(tanδ)的倒数；因此Q=1/tanδ。损耗有两种：取决于晶体结构的损耗和由外部因素引起的损耗。前者是本征损耗，如有序、对称性和声子振动。后者是由于晶粒度、缺陷、夹杂物和变形等因素造成的外在损失。在这一章中，作者从晶体结构的角度阐述了介质损耗的来源。理想且均匀的晶体结构构成了低损耗材料。大多数介质材料是顺电材料，具有反转对称性和高度对称性。总体而言，人们认为有序会导致高Q，这一点引起了许多研究者的怀疑。在复合钙钛矿的情况下，对称性从立方变为三角。有序性和对称性应该与结构进行比较。在这一章中，提出了高Q起源的三个必要条件，即高对称性、成分有序和成分密度。
So far, many microwave dielectric materials have been investigated for a range of telecommunication applications. In dielectrics, the three main dielectric properties are quality factor ( Q ), dielectric constant and temperature coefficient of resonant frequency. Among these, the most essential dielectric property is Q . More specifi-cally, Q is the inverse of the dielectric loss (tan δ ); thus Q = 1/tan δ . There are two kinds of losses: those depending on crystal structure and losses due to external factors. The former is intrinsic losses such as ordering, symmetry, and phonon vibration. The latter is extrinsic losses due to factors such as grain size, defects, inclusions and distortion. In this chapter, the authors present the origin of dielectric losses based on the crystal structure. An ideal and well-proportional crystal structure constitutes a low loss material. Most dielectric materials are paraelectrics with inversion symmetry i and high symmetry. In general, it is believed that ordering gives rise to a high Q , on which many researchers are casting doubt. In the case of complex perovskites, the symmetry changes from cubic to trigonal. Ordering and symmetry should be compared with the structure. In this chapter, three essential conditions for the origin of high Q such as high symmetry, compositional ordering and compositional density are presented.