燒結條件對鈉摻雜鈦酸鉛鋇(Pb0.3Ba0.7)TiO3陶瓷之電性影響分析

Abstract

本研究針對傳統固態反應法製備的(Pb0.3Ba0.7)TiO3陶瓷，摻雜2到14 mol% Na+，及利用不同原物料製備鈉摻雜(Pb0.3Ba0.7)TiO3，搭配不同氣氛之燒結條件，探討摻雜物、原物料、以及燒結氣氛對於電性的影響。實驗上以低電阻率、高介電常數與高介電損失做為目標，以便未來研究發熱及遠紅外線放射之應用。 實驗中以PbTiO3及BaTiO3作為原物料，並且摻雜8 mol% Na+的(Pb0.3Ba0.7)TiO3陶瓷不僅能夠保持化學計量比，同時也有較低的電阻、較大的介電常數和介電損失。材料的阻抗分析在柯爾圖上為一個類似半圓形狀，經由擬合得到表現接近電容之CPE (恆定相元素) 與電阻元件的並聯之等效電路。在霍爾量測結果顯示為p型，證實鈉取代A位置以作為受體摻雜物。 接著(Pb0.3Ba0.7)TiO3 + 8 mol% Na+在三種不同氣氛下進行燒結，分別為N2、O2，及兩階段式N2與O2，電性彼此類似且都比空氣下燒結更佳，等效電路皆為接近電容表現之CPE與電阻元件的並聯。定量分析上兩階段燒結可以保持化學計量比，而N2、O2下燒結則稍微偏離化學計量比。 適當的延長兩階段燒結的O2熱處理時間，可使材料有更低的電阻率、更高的介電常數，及維持高的介電損失。其主要機制是先藉由N2下燒結增加氧空缺數量，接著再以長時間O2熱處理將材料本質的氧空缺和N2下誘發的氧空缺進行填補，得到大量的電洞作為電荷載子。然而在3和4小時的O2熱處理時，載子遷移率有明顯增加的趨勢，推測材料中之氧空缺盡數被填補完畢，使氧離子進入晶格間隙位置，並伴隨著高遷移率的電洞。因為間隙氧離子與被束縛之電洞產生相消，於4個小時O2熱處理時，載子濃度有一明顯的下降，並在9小時的O2熱處理下，間隙氧離子與被束縛之電洞盡數相消使載子遷移率降低。

(Pb0.3Ba0.7)TiO3 ceramics doped with 2 to 14 mol% Na+ were prepared using a conventional solid-state-reaction method. The effects of dopants, raw materials and sintering atmosphere on the electrical properties were discussed. In the experiment, the electrical properties of materials with low resistivity, high dielectric constant and high dielectric loss were targeted so as to study the application of heat and far infrared radiation in the future. In the experiment, the (Pb0.3Ba0.7)TiO3 ceramics with PbTiO3 and BaTiO3 as the raw materials doped with 8 mol% Na+ was not only able to maintain the stoichiometric ratio, but also had lower resistivity, larger dielectric constant and dielectric loss. The impedance analysis of the material was a semicircular shape on Cole-Cole plot. The equivalent circuit of the CPE (constant phase element) similar to capacitance in parallel with the resistance element was obtained by fitting. The results of the Hall measurements were shown as p-type, confirming that sodium substituted the A-site as a acceptor dopants. Then (Pb0.3Ba0.7)TiO3 + 8 mol% Na+ were sintered in three different atmospheres, which were N2, O2, and two-step N2 and O2 respectively. The electrical properties were similar to each other and were better than those sintered in air. All the equivalent circuits were the CPE (constant phase element) similar to capacitance in parallel with the resistance element. Quantitative analysis of the two-step sintering was able to maintain the stoichiometric ratio, while those of N2, O2 sintering slightly deviated from the stoichiometric ratio. By properly increasing the O2 heat treatment time of two-step sintering, (Pb0.3Ba0.7)TiO3 + 8 mol% Na+ could have lower resistivity, higher dielectric constant, and maintain high dielectric loss. The main mechanism was increasing the number of oxygen vacancies by sintering under N2. Then, the oxygen vacancies in the material itself and those induced by N2 were filled with long time O2 heat treatment to obtain a large number of holes as charge carriers. However, under 3 and 4 hours O2 heat treatment, the carrier mobility increased significantly. It can be inferred that all the oxygen vacancies in the material were filled so that the oxygen ions entered the interstitial site and were accompanied by high mobility holes. Since the oxygen ions on interstitial site and trapped holes were eliminated each other, there was a significant decrease in the carrier concentration under 4 hours O2 heat treatment. And all the oxygen ions on interstitial site were eliminated by trapped holes under 9 hours O2 heat treatment, which decreased the carrier mobility.