Electrical properties and Ferroelectric Phase Transition of Donor-Doped Barium Titanate
| Autor: | Sheng-Cheng Liou, 劉信成 |
|---|---|
| Rok vydání: | 1993 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 81 PTC鈦酸鋇之商品化應用已超過三十年,但是仍無法合理解釋為什麼室溫電 阻係數會隨著添加量而改變 以往研究各種摻雜施體的含量約在0.3％摩耳 比時室溫電阻值最低,遠離0.3％摩耳比時室溫電阻率均增加,相對使ρ／ ρ 值減少本研究為瞭解添加 Sm,Nd 和 Pr 三 室溫電阻率差異較大的元 素(Fig. 1) 之電導機構, 改變不同的含量測試電阻率,晶格常數, 介電 常數及飽和極化值等隨溫度變化的改變以了解晶界上電子能障減少或消失 的原因另外,為瞭解不同取代型式對鈦酸鋇半導體之電導機構的影響,實驗 中亦添加Nb對其做初步的探討由實驗結果中顯示添加Sm,Nd 和 Pr 其室溫 電阻率未見有甚大的差異此結果與以往報告有所不同(Fig.1) 並且由X- ray 繞射結果可知所添加之元素其室溫電阻率與在正方相的c/a值有密切 的關係而添加高含量的元素其居禮溫度有降低的趨勢,此結果有必要進一 步了解 Donor-doped semiconducting BaTiO has a remarkable property of positive temperature coefficient of resistivity(PTC). Although PTC BaTiO has been in use for more than 30 years,it is difficult even today to explain the resistivity at room temperature as a function of doping content. In past studies, the addition of 0.3 at％ of donor dopes to BaTiO a dramatic decrease in the resistivity is observed at room temperature. Beyond this optimum doped, the room temperature resistivity will increase and the amount of increase depends on the kind of donors. The purpose of this study is to understand the conduction mechamism of Sm, Nd and Pr doped BaTiO which show large difference of room temperature resistivity.(Fig.1)We measured the variations of resistivity, lattice constant and saturation polarization of various amount donor - doped BaTiO. The measurementswill be under different temperature ranges.From the resultsofthose measurements willbe hopefully to understand the causes ofthediminished or decreased energy barrier at grain boundaries. In order to understand effect of different substitution type on conduction mechanism of semiconducting BaTiO, Nb is also used to as donor. From the results of ρ-T of Sm, Nd, and Pr doped BaTiO, We found that there is no much room temperature resistivity difference among those donors. This is results is different from that of O.Saburi. By examing X-ray diffraction results, the room temperature resistivity of donor-doped BaTiO is believed to be close-related to c/a ratio of tetragonal phase. Also, high room temperature resistivity for higher doping concentration samples is may be to shifting the Curie temperature to lower temperature. Although this result has to be examined in more detail. |
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