低價數補償Ba1-xMx(Fe0.5Nb0.5)1+x/4O3(M = Na, K)系列之介電性質研究

The Dielectric Properties of Low-Valence Compensation of Ba1-xMx(Fe0.5Nb0.5)1+x/4O3(M = Na, K) System

廖琨逢(Kun-Feng Liao)

指導教授 ： 張益新

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/碩士(2009年)

https://doi.org/10.6827/NFU.2009.00083

摘要

本研究係以複合型鈣鈦礦結構Ba(FeNb) 0.5O3 (BFN) 為主體材料，並以低價數之Na及K離子來取代Ba離子位置，以製備出Ba1-xMx(Fe0.5Nb0.5)1+x/4O3(M =Na, K)之複合型鈣鈦礦陶瓷體。本研究主要是以固態反應法合成Ba1-xNax(Fe0.5Nb0.5)1+x/4O3 (BNFN) (x = 0~20 mol%)與Ba1-xKx(Fe0.5Nb0.5)1+x/4O3 (BKFN) (x = 0~20 mol%)系統及其結構與介電性質研究。
本研究成功的以兩階段固態反應法合成Ba1-xMx(Fe0.5Nb0.5)1+x/4O3(M =Na、K)之複合型鈣鈦礦陶瓷體。由結果顯示，BNFN及BKFN陶瓷粉末分別在1000℃煆燒4~8個小時皆可形成BFN單一相之結構；在摻雜低價離子後，可發現其煆燒與燒結溫度降低約100~200℃。
在BNFN系列中，隨著Na摻雜量上升，其晶體結構由立方晶體轉變為斜方晶體。BNFN與BKFN隨著摻雜量增加，其晶格常數皆有變小的趨勢。從SEM分析結果顯示，當Na及K在高摻雜量時，發現顆粒有縮小的現象，且顆粒之形貌較不一。
在介電性質方面，隨著Na及K摻雜量上升，低價補償機制產生的電偶極數增加，介電常數有提高的趨勢。此外BNFN與BKFN之介電行為皆發現一步階狀介電遲緩曲線，且在低溫區產生高介電峰值，使居里溫度往低溫移動。當Ba0.8Na0.2(Fe0.5Nb0.5)1.05O3陶瓷體在溫度300 ~ 473 K及頻率在1 kHz之介電常數約為6×104~1.3×105，其介電損失下降至一飽合值狀態約為0.25。
陶瓷體BNFN或BKFN不論添加量多少，其介電性質均隨頻率的減少而增加，而介電曲線涵蓋一寬廣的溫度範圍，暗示著BNFN與BKFN介電陶瓷均為典型之強介電遲緩體材料，且在低頻範圍內擁有大量的方向性極化以及空間電荷極化。由於燒結過程中晶界與晶粒的擴散速度不同，導致晶界的阻抗遠大於晶粒，而晶粒由於低價數補償之關係形成導電性較高的晶粒，因此也形成晶界層電容產生高電容量。

關鍵字

Ba(FeNb)0.5O3 ； 介電特性 ； 價數補償

並列摘要

In this investigation, an complex perovskite structure Ba(FeNb) 0.5O3 (BFN) was chosen as the host material and doped with uni-valence Na+ and K+ ions which substitute the Ba2+ ion to form Ba1-xNax(Fe0.5Nb0.5)1+x/4O3 (BNFN) and Ba1-xKx(Fe0.5Nb0.5)1+x/4O3 (BKFN) ceramic using a solid state reaction.
The XRD results indicate that a single perovskite phase was obtained when the BNFN and BKFN powder were calcined at 1000°C for 4 ~ 8 hr. The best relative density for BNFN and BKFN were obtained when the samples were sintered at 1100 to 1150°C for 8 hr. For BFN doped with uni-valence of Na and K ions, the phase formation temperature and sintered temperature can be decreased about 100 to 200 °C.
When doping Na+ concentration is increasing, the crystal structure is transforms from cubic to the orthorhombic structure for the BNFN. The results from the unitcell software indicate that the lattice parameters decrease with increasing the doping Na+ or K+ concentrations.
The SEM results indicate that the surface morphology of BFN ceramics doped with high Na+ and K+ ion concentrations exhibits small grain sizes. When the doping concentrations increase continuously, the grain sizes were decreased but uniform than the others.
When increasing the Na+ and K+ ion concentration, the dielectric constant was increased owing to the uni-valence compensation produce dipoles was raised. The step-like dielectric relaxor cure was obtained for the BNFN and BKFN ceramics. However, the high dielectric constant curve appeared in low temperature, which can shift Curie point to low temperature range. The dielectric constant and loss of Ba0.8Na0.2(Fe0.5Nb0.5)1.25O3 ceramics is 6×104 ~ 1.3×105 and 0.25 with temperature range of 300 ~ 473 K and frequency of 1 kHz.
The temperature-dependent dielectric constant and loss curves measured at temperature range of 300 ~ 473 K and frequency of 1 kHz indicate that the samples exhibit a typical relaxor behavior with a broad temperature range which was contributed by orientation and space charge polarization. In sintered process, the diffusion of grains and grain boundary were different, and high oxygen diffusion coefficient at the grain boundary leads to the extent of oxidation and higher resistively in the grain boundary layers. Because the uni-valence compensation mechanism, the grains is form an high conductive grains.

並列關鍵字

Ba(FeNb)0.5O3 ； dielectric property ； valence compensation

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