光学浮区法制备新型高温超导单晶

发布时间：2018-01-04 15:40

本文关键词：光学浮区法制备新型高温超导单晶　出处：《东南大学》2016年硕士论文　论文类型：学位论文

【摘要】：对于高Tc铜氧化物超导体来说,空穴载流子浓度对正常和超导态性质有着非常重要的作用,理解超导与载流子浓度之间的关系是阐述超导机理非常重要的一步。大量研究致力于阐述超导转变温度Tc与二维Cu-O面上氧含量也就是空穴载流子浓度的关系。在Bi-2212系统中,发现通过改变载流子浓度,Tc可以在很大的范围内变化。对于Bi-2212体系来说,控制载流子浓度可以通过离子掺杂和气氛退火改变氧含量及分布来实现。Bi系的载流子是空穴并且Cu02面的空穴载流子浓度决定晶体的超导转换温度Tc,而空穴载流子浓度决定于氧含量,因为每个多余的氧原子会产生两个空穴。大量的实验表明,Bi-2212单晶的氧含量和分布对其超导性质有非常大的影响。论文目的是通过光学浮区法制备高质量的Bi-2212单晶,光学浮区法作为一种单晶制备的方法,可以制备大块高质量的Bi-2212单晶。然后将解理的单晶进行退火处理,分为空气中不同温度下的退火和相同温度下不同氧压下的退火。研究退火对单晶氧含量的影响,由此分析退火对Bi-2212单晶结构和超导性质的影响。首先,将Bi-2212单晶在空气中不同温度下退火,退火温度分别为300℃、400℃、450℃、500℃和600℃。对所有的退火样品利用XRD、SEM、和电磁输运(p-T和M-T)进行物性测量。XRD结果表明单晶为正交晶格结构,随着退火温度的增加单晶c轴的值减小,也就是氧含量增加。而p-T和M-T数据结果表明,超导转变温度Tc随着退火温度增加而减小。这个结果表明退火温度对单晶的氧含量有影响,使得单晶的c轴参数和超导温度Tc都发生改变。然后,将Bi-2212单晶在450℃进行不同氧压下的退火,退火氧压分别为10bar和100 bar。对退火后的单晶样品利用XRD、SEM和电磁输运(p-T和M-T)进行物性测量。结果表明高氧压退火得到过掺杂单晶,单晶的Tc随着退火氧压的增加而减小,退火氧压在很大程度上影响了样品的超导转换温度Tc。而XRD数据的结果表明单晶的c轴晶格参数随着退火氧压的增加而变小。Tc和c轴晶格参数的关系表明Tc的变化与Bi-O层和Cu-O层氧含量增加和氧重新分布有关。测量单晶在不同大小外加磁场下的R-T,外加磁场分别平行和垂直于c轴。由此可以得到单晶不同方向的上临界场μHc2和温度T的关系图,可以看出Bi-2212单晶具有各向异性的本质。根据WHH理论,得到T=0时不同方向上的μHc2(0),由此可计算Γ=μH-2.(0).μHc2//(0),这个值随着退火氧压的增加而减小,表明单晶的各向异性随着退火氧压增加而变小。
[Abstract]:For the high Tc cuprates, hole concentration plays a very important role in the normal and superconducting properties, the understanding of the relationship between superconductivity and carrier concentration is on the superconducting mechanism is an important step. A lot of research aims to expound the superconducting transition temperature Tc and 2D Cu-O surface oxygen content is between hole concentration. In Bi-2212 system, by changing the carrier concentration, Tc can change in a large range. For Bi-2212 system, the carrier can control the carrier concentration by ion doping and annealing changed the oxygen content and distribution system is to achieve the.Bi superconducting transition temperature Tc hole and the hole concentration determine crystal Cu02 the hole concentration and depends on the oxygen content, because each extra oxygen atom will produce two holes. A large number of experiments show that Bi-22 The oxygen content of 12 single crystal and distribution has great influence on the superconducting properties. The purpose of this paper is to prepare high quality Bi-2212 single crystal by optical floating zone technique, as a method of preparation of single crystal optical floating zone method can prepare bulk high quality Bi-2212 single crystal. Then single crystal cleavage annealing, divided into different annealing oxygen pressure under different temperatures and different annealing temperature in air. The effects of Annealing on the oxygen concentration, the analysis of the effect of Annealing on Bi-2212 crystal structure and superconducting properties. Firstly, the Bi-2212 single crystal in the air under different temperature and annealing, the annealing temperature was 300 degrees. 400 degrees, 450 degrees, 500 degrees and 600 degrees. For all the annealed samples by XRD, SEM, and electromagnetic transport (p-T and M-T) by physical property measurement results show that single crystal.XRD orthogonal lattice structure, with the increase of annealing temperature of single crystal c axis value reduction Small is the increase of oxygen content. The p-T and M-T data. The results show that the superconducting transition temperature Tc decreases with the increase of annealing temperature. The results showed the effect of oxygen content on the crystal annealing temperature, the c axis parameters of single crystal and temperature superconducting Tc are changed. Then, the Bi-2212 single crystal under different oxygen pressure the annealing at 450 DEG C, annealing oxygen pressure were 10bar and 100 bar. with XRD single crystal samples after annealing, SEM and electromagnetic transport (p-T and M-T) were measured. The results show that the properties of high oxygen pressure annealing have been doped single crystal single crystal, Tc decreases with the increase of annealing oxygen pressure, annealing oxygen pressure greatly influences the superconducting transition temperature of Tc. samples and XRD data showed that the relationship between C axis crystal lattice parameters increase with the annealing oxygen pressure decreases.Tc and C axis lattice parameters showed that Tc changes with Bi-O layer and Cu-O layer of oxygen content The increase and redistribution of oxygen. Measuring single crystal in different size under applied magnetic field R-T, the magnetic field is parallel and perpendicular to the c axis. The diagram of critical field Hc2 and temperature T so we can get the single crystal in different directions, we can see that the Bi-2212 crystal is anisotropic in this matter. According to the theory of WHH T=0 when the different directions of the Hc2 (0), from which we can calculate the gamma = H-2. (0). Hc2// (0), this value decreases with the increase of annealing oxygen pressure, the anisotropic single crystal with the increase of annealing oxygen pressure becomes smaller.

【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O782

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