【介電性】介電功能陶瓷

     介電材料是指在外電場作用下能發生極化、電導、損耗和擊穿等現象的材料，主要包括電容器介質材料和微波介質材料2大體系。微波介電材料主要用於製造介質諧振器、微波集成電路及片與元件和家用微型平面天線等微波器件。當介電材料用於製造電容器，則要求材料的電阻率高，介電常量大。

      今天就讓我們來了解2個介電材料吧~

      下期預告：電極材料專題。

Influence of (Mg1/3Nb2/3) complex substitutions on crystal structures and microwave dielectric properties of Li2TiO3 ceramics with extreme low loss

Mg1/3Nb2/3取代對極低損耗Li2TiO3陶瓷晶體結構和微波介電性能的影響

 Authors: Huan-Huan Guo, Di Zhou, Li-Xia Pang, Jin-Zhan Su

Volume 4, Issue 4, Pages 368-382

A systematic investigation of the Li2Ti1-x(Mg1/3Nb2/3)xO3 (0.1 ≤ x ≤ 0.35) solid solutions synthesized by traditional solid-state reaction method is reported in this work. 

通過傳統固相反應法合成了Li2Ti1-x（Mg1/3Nb2/3）xO3（0.1≤x≤0.35）固溶體，並進行了系統性地研究。

In the composition range of 0.1 ≤ x ≤ 0.25, a monoclinic rock salt structured solid solution was formed. When x increased to 0.3, a phase transition from monoclinic to cubic phase, along with an order-disorder phase transition, was observed. 

在0.1≤x≤0.25的組成範圍內，形成單斜巖鹽結構固溶體。當x增加到0.3時，觀察到從單斜相到立方相的相變，以及有序-無序相變。

With x increased from 0.1 to 0.35, the microwave permittivity (εr) and temperature coefficient of resonant frequency (TCF) of the Li2Ti1-x(Mg1/3Nb2/3)xO3 ceramics decreased linearly from 21.0 to 18.6, +27.1 to −19.4 ppm/°C, respectively. 

當x從0.1增加到0.35時，Li2Ti1-x（Mg1/3Nb2/3）xO3陶瓷的微波介電常數（εr）和共振頻率溫度係數（TCF）分別從21.0線性下降到18.6，從+ 27.1下降到-19.4 ppm /°C。

The Li2Ti0.75(Mg1/3Nb2/3)0.25O3 ceramic sintered at 1170 °C shows high performance of microwave dielectric properties with a εr ∼19.6, a Qf (Q = quality factor = 1/dielectric loss; f = resonant frequency) ∼109,770 GHz (at 7.7 GHz) and a near zero TCF ∼ + 1.2 ppm/oC. 

在1170℃燒結的Li2Ti0.75（Mg1/3Nb2/3）0.25O3陶瓷顯示出高性能的微波介電性能，εr~19.6，Qf（Q =品質因數= 1 /介電損耗; f =諧振頻率）~109,770 GHz（7.7GHz）和接近零的TCF~ +1.2 ppm/°C。

Moreover, the burying sintering process can reduce the volatilization of lithium so that the porosity of Li2Ti0.75(Mg1/3Nb2/3)0.25O3 ceramic was reduced effectively, which made Li2Ti0.75(Mg1/3Nb2/3)0.25O3 ceramic promising for future applications.

此外，埋燒工藝可以減少鋰的揮發，從而有效降低Li2Ti0.75（Mg1/3Nb2/3）0.25O3陶瓷的孔隙率，使Li2Ti0.75（Mg1/3Nb2/3）0.25O3陶瓷有希望得到應用。

Selected area electron diffraction patterns, high-resolution transmission electron microscopy, Raman and far-infrared spectra were employed to study the relation between crystal structure and microwave dielectric properties in detail.

通過選區電子衍射圖，高分辨透射電子顯微鏡，拉曼光譜和遠紅外光譜，詳細研究了晶體結構與微波介電性能之間的關係。

文中部分圖片：

晶體結構變化：單斜相→立方相

Fig. 2. (a, b, c, d) SAED patterns of Li2Ti1-x(Mg1/3Nb2/3)xO3 (0.1 ≤ x ≤ 0.25) with monoclinic phase viewed along the [1

晶粒大小、微波介電性能隨成分的變化

Fig. 4. The mean grain size (a), density (b) and microwave dielectric properties εr, Qf (c) and TCF (d) of the Li2Ti1-x(Mg1/3Nb2/3)xO3 (0.1 ≤ x ≤ 0.35) ceramics sintered at optimal temperatures as a function of x value

燒結溫度對Li2Ti0.75（Mg1/3Nb2/3）0.25O3陶瓷介電性能的影響

Fig. 9. (a ∼ e) SEM images of the LTMN0.25 ceramics sintered at various temperatures. (f) εr and Qf values of the LTMN0.25 ceramics sintered at various temperatures for 2 h. (g ∼ k) Statistical histogram of grain size in the SEM images. (l) Variation of bulk density and mean grain size as a function of sintering temperature.

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Phonon characteristics and dielectric properties of BaMoO4 ceramic

BaMoO4陶瓷的聲子特性和介電性能

 Authors: En-Cai Xiao, Jianzhu Li, Jing Wang, Chao Xing, Mei Guo, Hengyang Qiao, Qing Wang, Ze-Ming Qi, Gang Dou, Feng Shi

Volume 4, Issue 4, Pages 383-389

BaMoO4 ceramic was prepared using a conventional solid-sintering method. 

用常規固態燒結方法製備了BaMoO4陶瓷。

It was observed that the sample is a pure BaMoO4 with a tetragonal scheelite structure by analyzing X-ray diffraction data. Scanning electron microscopy characterized the dense sample with uniform grains. 

通過分析X射線衍射數據，觀察到樣品是具有四方白鎢礦結構的純BaMoO4。掃描電子顯微鏡表明樣品緻密，且晶粒均勻。

The phonon modes were analyzed by Raman and Far-infrared reflection spectra, and the phonon characteristics were studied. 

通過拉曼光譜和遠紅外反射光譜分析其聲子模式並研究了其聲子特性。

The intrinsic properties of the sample were calculated by the four-parameter semi-quantum model as well as the Clausius-Mosotti & damping equations, and the results were of εr = 9.388 and tanδ = 4.760 × 10−4, εr = 9.798 and tanδ = 6.445 × 10−4, respectively, which agrees well with the experimental values (εr = 9.84, tanδ = 5.0 × 10−4). 

通過四參數半量子模型以及Clausius-Mosotti方程和阻尼方程計算了樣品的本徵性質，結果分別為εr= 9.388，tan δ= 4.760×10-4，εr= 9.798，tan δ= 6.445×10-4，與實驗值吻合良好（εr= 9.84，tan δ= 5.0×10-4）。

The contributions to dielectric properties of each mode were investigated, and the results indicate that the external mode (Eu) yield greatest contribution to intrinsic permittivity and loss.

實驗研究了每種模式對介電性能的貢獻，結果表明外部模式（Eu）對本徵介電常數和損耗的貢獻最大。

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https://www.sciencedirect.com/science/article/pii/S2352847818300686

       

     最後再向大家介紹一下我們閃亮亮的JMAT期刊。它的全稱是Journal of　Materiomics，是由中國矽酸鹽學會和Elsevier合作出版的英文期刊,現已在ScienceDirect上發布了第四卷第四期（2018年），點擊文末「閱讀全文「可自由獲取所有論文全文。