【摘要】：氧空位由于其特定的光吸收性能因此也被稱為F心或色心,也是氧化物中無(wú)處不在的點(diǎn)缺陷,更是造成氧化物各種屬性的主要誘因。例如,在足夠低的溫度下可以成為超導(dǎo)體的SrTi03,隨著氧空位濃度的增加,SrTiO3可以從半導(dǎo)體轉(zhuǎn)變?yōu)榻饘賉1]。此外,氧空位在確定高溫超導(dǎo)銅氧化物超導(dǎo)體的臨界溫度[2],半導(dǎo)體氧化物磁性能[3],和導(dǎo)體催化行為等起著決定性的作用[4]。在足夠高的溫度下,跳躍運(yùn)動(dòng)的氧空位又對(duì)交流電導(dǎo)有重大的貢獻(xiàn)。因此,氧空位在氧化物的高溫介電性能中占主導(dǎo)地位[5-9]。氧空位最令人感興趣的研究?jī)?nèi)容之一就是氧空位本身其實(shí)是具有一個(gè)固有的非均勻分布,導(dǎo)致在氧化物中他們會(huì)出現(xiàn)自發(fā)有序的狀態(tài)。這種現(xiàn)象就是所謂的相分離或者條紋相,在高溫超導(dǎo)體[10,11]和巨磁電阻[12-14]中引起了濃厚的興趣。在鐵電材料中,自發(fā)有序的氧空位形成直線或者平面群是鐵電疲勞和老化的主要原因[15-18]。根據(jù)之前的報(bào)道,氧空位有序作為電荷有序的一種,它可以導(dǎo)致介電弛豫或介電異常[19-24]。我們的實(shí)驗(yàn)結(jié)論可以很好地描摹多數(shù)氧化物中的氧空位它們自發(fā)有序的過(guò)程。在我們的工作中,分別對(duì)TiO2,MgO,TeO2和LiNbO3單晶樣品進(jìn)行了系統(tǒng)的介電性能研究,得到了以下結(jié)果:(1)在較寬的溫度區(qū)間(室溫-700 ℃)和較寬的頻率區(qū)間(100 Hz-1 MHz),系統(tǒng)地研究了 Ti02的介電方面的性能。介電測(cè)試顯示了 Ti02單晶中存在三個(gè)溫度區(qū)域:在區(qū)域Ⅰ(T≤ 200 ℃)中,由氧空位電離產(chǎn)生的電子在Ti02單晶的介電性能占主導(dǎo)地位,出現(xiàn)的弛豫1由于Ti4+和Ti3+離子之間的電子跳躍導(dǎo)致。在區(qū)域Ⅱ(200 ℃-500 ℃)中,氧空位團(tuán)簇是引起相變的主要原因。在區(qū)域Ⅲ(T≥ 500 ℃)中,單個(gè)氧空位成為主要的載流子,他們?cè)诰Ц裰g的跳躍運(yùn)動(dòng)導(dǎo)致了弛豫2的產(chǎn)生。此外,勞厄衍射法證實(shí)了溫度區(qū)域Ⅱ內(nèi)氧空位有序過(guò)程的存在。密度泛函理論第一原理(DFT)計(jì)算顯示,氧空位有序狀態(tài)是比氧空位孤立狀態(tài)有利,氧空位團(tuán)簇有利于TiO2單晶中沿[001]方向形成一個(gè)線性鏈。(2)在較寬溫度范圍(300-1073 K)和頻率范圍(300 Hz-1 MHz),對(duì)MgO單晶樣品的介電性能進(jìn)行了研究。在400 K以下時(shí),MgO單晶樣品表現(xiàn)為內(nèi)部本征的介電響應(yīng),介電常數(shù)在9.5左右。在400 K以上,觀測(cè)到兩個(gè)相變過(guò)程。相變溫度大約都在800 K附近。第一個(gè)相變是由于氧空位從無(wú)序到有序引起,伴隨第一個(gè)相變的產(chǎn)生,MgO單晶呈現(xiàn)出了金屬絕緣體轉(zhuǎn)變行為(MIT)。第二個(gè)相變是由于氧空位從有序狀態(tài)變化到無(wú)序狀態(tài)導(dǎo)致。(3)在室溫到1073 K的溫度范圍頻率(100 Hz-2 MHz)范圍內(nèi),在TeO2單晶中僅發(fā)現(xiàn)一種介電異常。在～745 K處出現(xiàn)的異常顯示相變行為。氧空位的分布機(jī)制,被認(rèn)為是這種異常的原因。745K處的異常顯示相變過(guò)渡行為,被認(rèn)為與氧空位分布從無(wú)序狀態(tài)到有序狀態(tài)的變化相關(guān)聯(lián),隨著溫度升高,最終氧空位又變?yōu)闊o(wú)序狀態(tài)。(4)在室溫至1073 K的溫度范圍,頻率范圍(100Hz-2MHz)內(nèi),在三種不同氧空位濃度的LiNbO3單晶中,僅有氧空位濃度較高的GLN(淺摻雜)和BLN(深摻雜)發(fā)現(xiàn)了介電異常。在～607 K和～600 K處出現(xiàn)的異常顯示為相變行為。這說(shuō)明氧空位濃度會(huì)影響相變的產(chǎn)生,濃度過(guò)低時(shí)是沒(méi)有辦法出現(xiàn)相變的。對(duì)其中的氧空位含量較高的BLN進(jìn)行偏壓實(shí)驗(yàn)可以發(fā)現(xiàn),加偏壓后相變的溫度會(huì)向低溫方向轉(zhuǎn)移,說(shuō)明外加電場(chǎng)能夠有效調(diào)控有序過(guò)程。總結(jié)來(lái)說(shuō),氧空位是影響氧化物高溫介電性能的主導(dǎo)因素。
[Abstract]:Oxygen vacancies are also referred to as F-centers or color centers due to their specific light-absorbing properties, and are also the main causes of various kinds of properties of oxides. For example, SrTi03, which can be a superconductor at a sufficiently low temperature, can be converted from the semiconductor to the metal[1] as the oxygen vacancy concentration increases. In addition, the oxygen vacancy plays a decisive role in determining the critical temperature[2] of the high-temperature superconducting copper oxide superconductor, the magnetic properties of the semiconductor oxide[3], and the catalytic behavior of the conductor[4]. At a sufficiently high temperature, the oxygen vacancy of the jump motion has a significant contribution to the AC conductance. Therefore, the oxygen vacancy is dominant in the high-temperature dielectric properties of the oxide[5-9]. One of the most interesting studies of oxygen vacancies is that the oxygen vacancies themselves are inherently non-uniform, resulting in a spontaneous and orderly state in the oxides. This phenomenon is the so-called phase separation or fringe phase, which is of great interest in the high-temperature superconductors[10,11] and the giant magnetoresistance[12-14]. In ferroelectric materials, spontaneous and ordered oxygen vacancies form a straight line or a planar group is the main cause of ferroelectric fatigue and aging[15-18]. According to the previous report, the oxygen vacancy is ordered as a charge-ordered one which can lead to dielectric relaxation or dielectric anomalies[19-24]. Our experimental results can well trace the spontaneous and ordered process of oxygen vacancies in most oxides. In our work, the dielectric properties of TiO2, MgO, TeO2 and LiNbO3 single crystal samples were studied, and the following results were obtained: (1) in a wide temperature range (room temperature-700 鈩，

本文編號(hào)：2490011