【作者】 徐洁；

【导师】 张善涛；

【作者基本信息】 南京大学 ， 材料物理与化学， 2014， 硕士

【摘要】 钙钛矿结构氧化物具有非常丰富的物理性质,如铁电性、铁磁性、压电性、超导性等,这些丰富的物理内容为基础物理研究提供了广阔的平台。另一方面,钙钛矿结构氧化物在很多领域也表现出了巨大的应用前景,如磁存储、传感、催化等。因此,自上世纪五六十年代起,钙钛矿结构氧化物的研究逐渐得到重视。特别是近几十年来,由于在其中发现了巨磁电阻效应(Colossal Magnetoresistance)以及高温超导特性,钙钛矿结构氧化物更成为了关注和研究的焦点。本论文首先对钙钛矿结构氧化物的基本结构和常见性质进行了简单介绍,并针对其中的两类材料：1.钙钛矿结构的锰氧化物巨磁电阻材料；2.类钙钛矿结构的铜氧化物超导材料,具体分析了微结构调控对于其性质的影响。在此基础上进行了相关材料的制备以及性质的测试分析,具体如下：1.利用PbTiO3对LaMnO3进行了固熔。实验中,采用传统的固相烧结法制备了Pb1-xLaxTi1-xMnxO3 (x=0.20,0.40,0.50,0.60,0.80)系列的单相陶瓷。LaMnO3为具有正交相结构的A-type反铁磁绝缘体,而PbTiO3则为具有四方相结构的铁电绝缘体。当这两种成分进行掺杂时,由于pb2+离子的引入,会使得Mn的价态发生变化,从而引起局域的Mn3+-O2--Mn4+间的铁磁相互作用。而B位上Ti离子的引入,则又会使Mn离子的分布发生变化,进而影响Mn离子间的相互作用。当x=0.2时,样品具有四方相的结构,随着x的增大,结构会由四方相向正交相转变,并且晶格常数也随之减小。通过XPS对Mn的价态进行测定,当x=0.2、0.4时,Mn表现为+3价,而当x=0.5、0.6、0.8时,Mn则表现为+3价和+4价的混合。该结果与磁性质是相一致的,当x=0.2、0.4时样品表现出顺磁的性质。而当x=0.5、0.6、0.8时,由于Mn3+和Mn4+共存,超交换作用和双交换作用同时存在,样品表现出了铁磁和反铁磁共存的性质。该体系的样品均表现出绝缘体的性质,且电阻值随着x的增大而减小。而且对于x=0.8的样品,10K时的磁阻达到了-41.5%。我们推断,这些性质是由于样品中铁磁金属相和非铁磁绝缘体相共存所导致的,且随着x的改变,两个相的含量也会发生改变。2.对类钙钛矿结构的铜氧超导体进行了初期的探索。使用SrCuO2对SrCuO2进行了微量的成分调控。通过固相烧结的方法,制备了一系列的陶瓷样品,具体成分为：(1-y)La1.85Sr0.15CuO4+ySrCuO2,其中y=0.00,0.02,0.04,0.06。并在此基础上对y=0以及y=0.02的样品利用脉冲激光沉积的方法实现了薄膜的外延生长,对制得的薄膜通过流动氧气下退火的方式来减少氧空位的存在。XRD结果表明,退火后薄膜的衍射峰发生微小的偏移,这间接证明了氧空位的减少。但退火后样品的电学性质仍不理想,如何进一步减少氧空位是值得思考的问题。使用BaCuO2对YBa2Cu307进行了成分调控,使之成分为YBa3Cu4O9。利用脉冲激光沉积的方法对YBa3Cu4O9和YBa2Cu3O7两种成分进行了薄膜的制备。XRD结果显示薄膜的结构良好,并且通过在氧气氛围下的退火处理,部分样品也表现出了超导性质。更多还原

【Abstract】 The studies of oxides with perovskite structure started in 1950’s. In recent years, perovskite oxides have been a hotspot and attracted much attention due to the exciting discovery of high temperature superconductivity in cuprates and CMR (colossal magnetoresistance) effect in magnanites. There are fruitful physical properties in perovskite oxides, such as ferroelectricity, ferromagnetism, piezoelectricity and superconductivity, etc. These properties and their coupling effects inspire studies on them and investigating the working mechanism behind. Besides that, perovskite oxides also have great applied potential in many fields, such as storage, sensor and catalysis, etc.In the first chapter, a brief overview of perovskite oxides is introduced. Their structures and some fascinating properties are also mentioned. And then we mainly focus on two kinds of perovskite oxides, the perovskite manganite and the defective layered perovskite cuprates. The effects caused by different kinds of doping are also discussed.In others chapters, we have performed the study of some perovskite oxides. The samples are prepared and their structure, electrical and magnetic properties are investigated. The major results are:1. LaMnO3-PbTiO3 solutions.Single phase Pb1-xLaxTi1-xMnxO3 (PLTM100x, x=0.20,0.40,0.50,0.60, and 0.80) ceramics have been prepared and investigated. LaMnO3 (LMO) is an A-type antiferromagnetic insulator, while PbTiO3 (PTO) is a ferroelectric insulator. It is believed that the introduction of Pb2+ in A-site may bring local Mn4+thus local Mn3+-O2-Mn4+ferromagnetic interaction, whereas the introduction of diamagnetic cation of Ti4+ in B-site may dilute and disorder the magnetic interaction between magnetic cations, both will have effects on transport and magnetic properties.X-ray diffractions show all ceramics are crystallized into perovskite structures with tetragonal symmetry for PLTMO20 and orthorhombic symmetry for the other compositions. And the lattice parameters decrease with the incresing x. X-ray photoelectron spectroscopy results confirm that the Mn cations in PLTMO20 and PLTMO40 have the valence state of +3, whereas in other compositions, the Mn cations have mixed valences states of +3 and+4. With increasing x from 0.20 to 0.80, the materials change from superparamagnetic to coexisting ferromagnetic and antiferromagnetic magnetic behaviour whereas all compositions persist insulating behaviour. Especially, the PLTMO80 has a large negative magnetoresistance of-41.5% at 10 K with the applied filed of 2 T.We believe these properties are attributed to the coexistence of metallic ferromagnetic and insulating non-ferromagnetic phases.2. Some preliminary work on high Tc superconductive cuprate films(1) SrCuO2-modified LausSr0.15CuO4.Single phase ceramics of the compositions expressed as (1-y)La1.85Sr0.15CuO4+y SrCuO2 (y=0.00,0.02,0.04,0.06) are prepared. Based on the works on ceramics, La1.85Sr0.15CuO4 (y=0) and La1.83i5Sr0.1585CuO3.98(y=0.02) films are prepared by pulsed laser deposition (PLD). The XRD results indicate the films are epitaxial growth with good crystalline quality. As we know, the oxygen vacancies play an important role in electrical properties. The films are annealed in flowing oxygen to reduce oxygen vacancies. The XRD results show that the lattice parameters increase slightly by annealing, which indicates that annealing is helpful to reduce oxygen vacancies. However, the electrical properties still need further optimization.(2) BaCuO2-modified YBa2Cu3O7YBa3Cu4O9 and YBa2Cu3O7 films are prepared. The XRD results indicate the films are epitaxial growth with good crystalline quality. And in some annealed samples, we observe the existence of superconductivity. Further works are underway.更多还原