鈦酸鋇/鎳複合材料的功能特性

Functional Properties of BaTiO3/Ni Composites

黃永慶(Yung-Ching Huang)

指導教授 ： 段維新

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2006年)

https://doi.org/10.6342/NTU.2006.00555

摘要

多層陶瓷電容器是重要的被動元件，主要包含鈦酸鋇基之介電質以及金屬內電極。廣泛地使用金屬鎳或銅當成電極材料，主要為了較低電容器的價格。然而這些卑金屬與介電質燒結必須在還原氣氛下，因為於空氣中金屬容易受到氧化。已有許多方法已經被報導指出鈦酸鋇基地能夠保持高的絕緣電阻既使燒結於低氧分壓下。就本研究而言，鎳顆粒均勻地混合在鈦酸鋇粉末中。含鎳的鈦酸鋇陶瓷經由不同燒結條件及氧分壓加以燒結。添加鎳的鈦酸鋇複合材的微結構、緻密化行為、電性、鐵電性及鐵磁性均加以研究。
根據燒結氣氛下的氧分壓，有極少量的鎳離子可能固溶到鈦酸鋇中，取代鈦離子的位置。因此，鎳在鈦酸鋇中當成一個授體。其中鈦酸鋇的正方性及晶粒大小隨著鎳含量之增加而減少。當燒結於氮氣及1330度時，鎳在鈦酸鋇中的固溶量約為0.075-0.1 vol%。另外，鎳在鈦酸鋇的擴散距離係與燒結氧分壓有關。因此，在高還原氣氛下(10-7-10-8Pa)，鎳幾乎不再固溶及擴散於鈦酸鋇基地中。鈦酸鋇緻密化行為的差異受到鎳溶質的影響。鈦酸鋇晶粒大小也受到燒結氣氛影響。鈦酸鋇晶粒隨著氧分壓的降低，先增大，然後減小。
摻雜鎳的鈦酸鋇複合材其電性受到鎳的添加所影響。液相Ba6Ti17O40 及孔洞的出現會降低介電性質。當未摻雜的鈦酸鋇先還原在氧分壓為10-15 Pa，之後再燒結於N2 或 10-2-10-3 Pa時，鈦酸鋇則變為半導化。然而，部分鎳離子固溶於鈦酸鋇中，能改善鈦酸鋇的還原阻力。含鎳的鈦酸鋇於低氧分燒結後，電阻係數仍可高達1010 ohm×m及介電損失低於2 %。製程區間則可利用缺陷化學模式來建立，因而能製備出含鎳金屬之鈦酸鋇絕緣體材料。根據實驗的結果，更能推導出離子導電係數及還原平衡常數。
本實驗也得知，純鈦酸鋇是一個反鐵磁材料，但添加金屬鎳顆粒將會使複合材產生鐵磁性，飽和磁化值隨著鎳含量增加而上升。在鎳含量為35%時，飽和磁化值可以達到 25 emg/g。另一方面，在滲流理論值以下時，可以得到介電常數高於28,800，此現象能與滲流方程式吻合，其中滲流體積分率為0.35。

關鍵字

鈦酸鋇 ； 多層電容陶瓷 ； 鎳 ； 氧分壓 ； 授體 ； 固溶度 ； 缺陷 ； 微結構 ； 晶粒尺寸 ； 電阻係數 ； 介電損失 ； 介電常數 ； 鐵磁性 ； 滲流

並列摘要

Multilayered ceramic capacitors (MLCCs) composing BaTiO3 based dielectric and metallic inner electrodes are one the most important passive components. The electrodes materials such as Ni or Cu are widely used for reducing the cost of MLCCs. These base-metal electrodes (BME) capacitors have to be fired in a reducing atmosphere to avoid the oxidation of metals. Many approaches have been reported to maintain the insulation resistance of BaTiO3 based dielectrics even when they are sintered in low oxygen partial pressure. In the present study, the Ni particles are mixed with the BaTiO3 powders. The sintering of the Ni/BaTiO3 composites is carried out in different atmosphere with various oxygen partial pressures. The microstructure, densification behaviour, electrical, ferroelectric and ferromagnetic properties of Ni-doped BaTiO3 are measured.
Depending on the partial pressure in the sintering atmosphere, a very small amount of Ni ion may dissolve into BaTiO3 to replace Ti ion. The Ni2+ ion thus act as acceptor to BaTiO3. The tetragonality and grain size are thus reduced with the increase of Ni content. The solubility of Ni in BaTiO3 as sintered in N2 at 1330 oC is about 0.075-0.1 vol.% Ni. In addition, the diffuse distance of Ni in BaTiO3 matrix also depends on the oxygen partial pressure in the sintering atmosphere. The solubility of Ni in BaTiO3 is negligible as sintering is carried out in a highly reducing atmosphere (Po2=10-7-10-8Pa). The densification behaviour is affected by the Ni2+ solutes. The grain size of the Ni-doped BaTiO3 is also affected by sintering atmosphere. The grain size of BaTiO3 is increased and then decreased with the decrease of oxygen partial pressure.
The electrical properties of Ni-doped BaTiO3 are affected by the Ni addition. The presence of pores and the Ba6Ti17O40 phase degrades the dielectric properties of Ni-doped BaTiO3. The undoped BaTiO3 becomes semiconducting as sintering in Po2=10-15 Pa and then re-oxidized in N2 (Po2=1 Pa) or Po2=10-2-10-3 Pa. However, the solution of Ni2+ into BaTiO3 can improve the reduction resistance of BaTiO3. Electrical resistivity higher than 1010 Ω•m and dissipation factor lower than 2% are thus obtained in the Ni-doped BaTiO3 samples even they are sintered in a relatively low oxygen partial pressure. The process windows for the preparation of insulating BaTiO3-Ni can be built by applying defect models. According the experimental results, the ionic conductivity constant (Ki) and reduction equilibrium constant (KR) can be estimated.
The monolithic BaTiO3 is an anti-ferromagnetic material; the addition of metallic Ni particles introduces a ferromagnetic response into BaTiO3. The specific saturation magnetization increases with the increase of Ni content. For the BaTiO3/35%Ni composite, the specific saturation magnetization reaches a value of 25 emu/g. On the other hand, by adding an amount of Ni particles slightly below the percolation limit of the Ni particles can push the dielectric constant to a value as high as 28,800. The phenomena are well fitted by a percolation equation. The value of percolation threshold (Vc) as determined from the experimental data is 0.35.

並列關鍵字

BaTiO3 ； MLCCs ； Ni ； oxygen partial pressure ； acceptor ； solubility ； defect ； microstructure ； grain size ； electrical resistivity ； dielectric loss ； dielectric constant ； ferromagnetic ； percolation

參考文獻

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