介電弛豫現象是指電介質在外電場作用(或移去)後，從瞬時建立的極化狀態達到新的極化平衡態的過程。通過上一期推送，我們了解弛豫型鐵電材料，今天就讓我們了解下具有介電弛豫行為的殼聚糖冰-水凝膠材料和BaTiO3鐵電陶瓷吧！
下期預告：介電材料專題。
Dielectric relaxation of interfacial polarizable molecules in chitosan ice-hydrogelmaterials
殼聚糖冰-水凝膠材料中界面可極化分子的介電弛豫
Authors: Y.Q. Li, C.X. Zhang, P. Jia, Y. Zhang, L. Lin, Z.B. Yan, X.H. Zhou and J.-M. Liu*
Volume 4, Issue 4, Pages 35-43
The functionalities of hydrogel-based smart materials are highly related to the electrostatic interactions and molecular polarization associated with the polymer networks and encapsulated water droplets, and therefore the dielectric responses of the polarizable molecules in the polymer, water, and polymer-water interfaces are particularly attractive, where the properties of polymer-water interfacial molecules remain elusive.
水凝膠智能材料的功能與聚合物網絡及封裝的水滴的靜電相互作用和分子極化息息相關。因此，聚合物、水和聚合物-水界面處的可極化分子的介電響應尤具吸引力,而聚合物-水界面分子的性質目前仍然是個未解的難題。
Different from extensive dielectric relaxation spectroscopy studies on polymer hydrogel solutions, in this work we investigate the dielectric response of chitosan hydrogels below the water solidifying point (ice-hydrogels) so that the contribution of chitosan-water interfacial molecules can be isolated.
不同於廣泛的關於聚合物水凝膠的介電弛豫譜研究,在這個工作中我們針對的是殼聚糖水凝膠在低於凝固點時（冰凝膠）的介電響應。這樣殼聚糖-水界面分子的貢獻可以被分離出來進行研究。
It is revealed that the chitosan-water interfacial polarizable molecules have slow dielectric relaxation but large polarization compared with the chitosan chains and water molecules, and the dielectric relaxations beyond ∼104 Hz are substantially weak. The thermal activation energy of the dielectric relaxation for these interfacial polarizable molecules can be as large as 0.93 eV, i.e. 89.73 kJ/mol.
研究發現,殼聚糖-水界面可極化分子的介電弛豫緩慢，但與殼聚糖鏈和水分子相比具有較大極化值,且頻率大於∼104 Hz部分的介電弛豫大幅減弱。這些界面可極化分子的介電弛豫熱活化能可高達0.93 eV,即89.73 kJ/mol。
The present work provides a platform for characterizing the polymer-water electrostatic interactions and interfacial polarizable molecules, informative to understand the microstructure-property relationships of chitosan-based hydrogel materials.
這個工作提供了觀測聚合物-水靜電交互作用和及其界面可極化的分子的平臺,對理解殼聚糖基水凝膠材料的微觀結構和性能之間的關係具有很大幫助。
文中部分圖片：
微觀形貌
Fig. 2. Elastic diffuse scattering maps around the [(a), (b) and (c)] (100) and [(d), (e) and (f)] (110) Bragg peaks. The same color scales are used in (a)/(b) and (d)/(e). The arcs at Q ∼1.70 rlu are contamination Al scattering from the sample environment.
熱性能和化學結構分析
Fig. 3. (a) The measured DSC curves in the cooling and then heating cycle at a rate of 20 K/min, with arrows indicating the cycle. The measured FTIR spectra for pure chitosan (CS), acetic acid (AA), and the as-prepared hydrogels (CS-g-PAA) are presented in (b), see text for details.
介電弛豫
Fig. 4. The dielectric real part ε′(f) for water and ice at 273 K (a), where the data are taken from Ref. [54], and for dry chitosan powder at three different temperatures (b).
Fig. 5. (a) ∼ (c): The measured dielectric real part ε′, imaginary part ε″, and dielectric loss tanδ = ε″/ε′ at several frequencies as a function of temperature T for the as-prepared hydrogel sample (h = 0.93) in the cooling sequence from 330 K. Here Tw is the solidifying point of water droplets in the sample and Tw marks the peak position. (d): The evaluated frequency f. vs. Tmax relation from which the thermal activation energy Ea is evaluated via the Arrhenius law. (e) and (f): The evaluated ε′, ε″, and tanδ at T → Tw −0 as a function of frequency f.
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Oxygen-vacancy-related dielectric relaxation behaviours and impedance spectroscopy of Bi(Mg1/2Ti1/2)O3 modified BaTiO3 ferroelectric ceramics
Bi(Mg1/2Ti1/2)O3改性的BaTiO3鐵電陶瓷氧空位導致的介電馳豫行為和阻抗譜分析
Authors: Ming-Ding Li, Xin-Gui Tang*, Si-Ming Zeng, Yan-Ping Jiang, Qiu-Xiang Liu, Tian-Fu Zhang and Wen-Hua Li
Volume 4, Issue 3, Pages 194-201
Lead-free ferroelectric ceramics (1-x) BaTiO3–xBi(Mg1/2Ti1/2)O3 (x = 0.0–0.07) were synthesized by conventional solid state reaction method and the correlation of structure, dielectric, ferroelectric and impedance properties were investigated.
本工作採用常規固相反應法合成了無鉛鐵電陶瓷 (1-x) BaTiO3–xBi(Mg1/2Ti1/2)O3 (x = 0.0–0.07) ，研究了結構，介電，鐵電和阻抗特性的相關性。
It was found that Tm and εm showed decreasing trend with the increase of BMT content. The high-temperature dielectric relaxation behaviour was observed in all the samples.
結果發現隨著BMT含量的增加， Tm 和εm 呈下降趨勢。在所有樣品中觀察到高溫介電弛豫行為。
The activation energy calculated from impedance (Ea) and conductivity (Econd), which revealed that the relaxation behaviours were linked with the migration of OVs. The values of Ea were almost equivalent to Econd.
由阻抗（Ea）和電導率（Econd）計算的活化能表明馳豫行為與氧空位的遷移相關。Ea的值幾乎等於Econd。
It was concluded that the short-range hopping of oxygen vacancy contributed to the dielectric relaxation and long-distance movement of doubly ionized oxygen vacancies contributed to the conduction.
由此我們認為介電弛豫由氧空位的短程躍遷貢獻，而電導由雙電離氧空位的長距離運動貢獻。
On the other hand, with increasing BMT contents, it was found that P-E loops became slimmer and slimmer, which indicated the increase of relaxor behaviour.
另一方面，隨著BMT含量的增加，P-E回線變得更纖細，表明弛豫行為逐漸增強。
The temperature dependence of P-E loops for 0.98BT–0.02BMT ceramic clearly showed the transition process from ferroelectric to relaxed ferroelectrics.
P-E回線對0.98BT-0.02BMT陶瓷的溫度依賴性清楚地表明了從鐵電體到弛豫鐵電體的轉變過程。
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https://www.sciencedirect.com/science/article/pii/S2352847818300078
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。