与氧空位有序有关的介电现象研究
发布时间：2019-05-31 20:59
【摘要】：氧空位由于其特定的光吸收性能因此也被称为F心或色心,也是氧化物中无处不在的点缺陷,更是造成氧化物各种属性的主要诱因。例如,在足够低的温度下可以成为超导体的SrTi03,随着氧空位浓度的增加,SrTiO3可以从半导体转变为金属[1]。此外,氧空位在确定高温超导铜氧化物超导体的临界温度[2],半导体氧化物磁性能[3],和导体催化行为等起着决定性的作用[4]。在足够高的温度下,跳跃运动的氧空位又对交流电导有重大的贡献。因此,氧空位在氧化物的高温介电性能中占主导地位[5-9]。氧空位最令人感兴趣的研究内容之一就是氧空位本身其实是具有一个固有的非均匀分布,导致在氧化物中他们会出现自发有序的状态。这种现象就是所谓的相分离或者条纹相,在高温超导体[10,11]和巨磁电阻[12-14]中引起了浓厚的兴趣。在铁电材料中,自发有序的氧空位形成直线或者平面群是铁电疲劳和老化的主要原因[15-18]。根据之前的报道,氧空位有序作为电荷有序的一种,它可以导致介电弛豫或介电异常[19-24]。我们的实验结论可以很好地描摹多数氧化物中的氧空位它们自发有序的过程。在我们的工作中,分别对TiO2,MgO,TeO2和LiNbO3单晶样品进行了系统的介电性能研究,得到了以下结果:(1)在较宽的温度区间(室温-700 ℃)和较宽的频率区间(100 Hz-1 MHz),系统地研究了 Ti02的介电方面的性能。介电测试显示了 Ti02单晶中存在三个温度区域:在区域Ⅰ(T≤ 200 ℃)中,由氧空位电离产生的电子在Ti02单晶的介电性能占主导地位,出现的弛豫1由于Ti4+和Ti3+离子之间的电子跳跃导致。在区域Ⅱ(200 ℃-500 ℃)中,氧空位团簇是引起相变的主要原因。在区域Ⅲ(T≥ 500 ℃)中,单个氧空位成为主要的载流子,他们在晶格之间的跳跃运动导致了弛豫2的产生。此外,劳厄衍射法证实了温度区域Ⅱ内氧空位有序过程的存在。密度泛函理论第一原理(DFT)计算显示,氧空位有序状态是比氧空位孤立状态有利,氧空位团簇有利于TiO2单晶中沿[001]方向形成一个线性链。(2)在较宽温度范围(300-1073 K)和频率范围(300 Hz-1 MHz),对MgO单晶样品的介电性能进行了研究。在400 K以下时,MgO单晶样品表现为内部本征的介电响应,介电常数在9.5左右。在400 K以上,观测到两个相变过程。相变温度大约都在800 K附近。第一个相变是由于氧空位从无序到有序引起,伴随第一个相变的产生,MgO单晶呈现出了金属绝缘体转变行为(MIT)。第二个相变是由于氧空位从有序状态变化到无序状态导致。(3)在室温到1073 K的温度范围频率(100 Hz-2 MHz)范围内,在TeO2单晶中仅发现一种介电异常。在～745 K处出现的异常显示相变行为。氧空位的分布机制,被认为是这种异常的原因。745K处的异常显示相变过渡行为,被认为与氧空位分布从无序状态到有序状态的变化相关联,随着温度升高,最终氧空位又变为无序状态。(4)在室温至1073 K的温度范围,频率范围(100Hz-2MHz)内,在三种不同氧空位浓度的LiNbO3单晶中,仅有氧空位浓度较高的GLN(浅掺杂)和BLN(深掺杂)发现了介电异常。在～607 K和～600 K处出现的异常显示为相变行为。这说明氧空位浓度会影响相变的产生,浓度过低时是没有办法出现相变的。对其中的氧空位含量较高的BLN进行偏压实验可以发现,加偏压后相变的温度会向低温方向转移,说明外加电场能够有效调控有序过程。总结来说,氧空位是影响氧化物高温介电性能的主导因素。
[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，
本文编号：2490011
[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，
本文编号：2490011
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