二维层状材料CuMP2S6(M=Cr,V)多铁性质研究

STUDY ON MULTI-FERROIC PROPERTIES OF TWO-DIMENSIONAL LAYERED MATERIAL CuMP2S6(M=Cr,V)

位龙宇

11849278

硕士

材料工程

梅佳伟

2020-05-29

2020-07-15

哈尔滨工业大学

深圳

到目前为止对多铁性材料研究取得了大量的成果，但也存在着一些问题：第一类多铁材料的磁电耦合效应很弱；第二类多铁材料的铁电极化和居里温度较低，三维多铁材料降到二维尺度时铁电性和磁性的消失等等。这些问题限制了多铁材料的实际应用，但也引导研究者们进行不断的探索。自从石墨烯被发现以来，二维范德瓦尔斯材料取得了长足的发展，二维磁性，二维铁电以及二维多铁的报道层出不穷。多铁性在二维材料当中的存在形式十分的丰富，既包括Ⅰ类多铁、Ⅱ类多铁以及在它们之外的磁电耦合形式，对二维多铁的研究也有希望能够解决在传统单相多铁材料研究中面临的一些瓶颈问题。虽然有大量的研究者通过第一性原理计算等方法预测了很多二维多铁材料以及它们当中磁性、铁电性以及磁电耦合的存在形式，但由于材料较难合成，材料及其不稳定等因素，对这些材料的实验研究和验证相对较少。过渡金属硫代亚磷酸盐化合物是类似于过渡金属硫化物的范德瓦尔斯晶体，层与层之间的作用力较弱，能够轻易的通过机械剥离法从大块单晶上获得少层甚至单层样品。过渡金属硫代亚磷酸盐CuMP2S6(M=Cr,V)就代表了目前已发现的二维多铁材料当中的一种类型， 我们利用化学气相传输法制备出高质量的CuMP2S6(M=Cr,V)单晶，在实验方面对CuMP2S6(M=Cr,V)进行了一系列的研究，证明了CuMP2S6(M=Cr,V)大块样品当中存在弱多铁性，研究内容如下：（ 1 ） 利用化学气相传输法制备出较大尺寸和较高质量的CuMP2S6(M=Cr,V)单晶，对制备出的单晶进行了X 射线衍射以及能量散射X光谱的测量，进一步确认了单晶的质量，为后续的物性表征奠定了前提和基础。（2）通过对磁化率的测量以及对磁化率曲线的分析并结合比热的测量结果，确认了CuCrP2S6 的反铁磁相变温度TN1=32 K，CuVP2S6 居里温度TC=20 K。（3）通过对单晶样品介电常数、比热、变温拉曼、电滞回线的测量和结果分析，CuVP2S6 和CuCrP2S6 在常温下均为铁电体，CuCrP2S6 在173 K 时时发生结构相变，在155 K 以下为反铁电体。CuVP2S6 的铁电转变居里温度在常温以上。（4）通过对磁化率和介电常数数据的进一步分析发现CuMP2S6(M=Cr,V)之间的磁电耦合较弱，符合这类体系材料是第Ⅰ类多铁材料的理论预测。

So far, a lot of achievements have been made in the study of multiferroic materials, but there are still some problems: the first kind of multiferroic materials have weak magnetoelectric coupling effect; the second kind of multiferroic materials have low ferroelectric polarization and Curie temperature; the three-dimensional multiferroic materials lose ferroelectricity and magnetism when they fall to the two-dimensional scale, etc. These problems limit the practical application of multiferroic materials, but also guide the researchers to carry out continuous exploration. Since the discovery of graphene, two-dimensional van der Waals materials have made great progress. Two-dimensional magnetism, two-dimensional ferroelectricity and two-dimensional multiferrous have been reported in endlessly. There are many forms of multiferrousness in two-dimensional materials, including class I multiferrousness, class II multiferrousness and magnetoelectric coupling forms outside of them. Theresearch on two-dimensional multiferrousness is also expected to solve some bottleneck problems in the research of traditional single-phase multiferrousness materials.Although a large number of researchers have predicted many two-dimensional multiferroic materials and the existing forms of magneti sm, ferroelectricity and magnetoelectric coupling through the first principle calculation and other methods, due to the factors such as difficult synthesis of materials, material and its instability, the experimental research and verification of these materials are relatively few. The transition metal thiophosphite is a kind of van der Waals crystal, which is similar to the transition metal sulfide. The force between layers is weak. It can easily obtain a few layers or even a single layer of samples from a large single crystal by mechanical stripping. The transition metal thiophosphite CuMP2S6(M=Cr,V) represents one of the two-dimensional multiferrous materials that have been found at present. The high-quality single crystal of CuMP2S6(M=Cr,V) was prepared by chemical vapor transport method. A series of experimental studies on CuMP2S6(M=Cr,V) were carried out to verify the existence of multiferrous in the bulk samples of CuMP2S6(M=Cr,V). The research contents are as follows:(1) The large-scale and high-quality single crystal of CuMP2S6 (M=Cr,V) was prepared by chemical vapor transport method. The X-ray diffraction and energy scattering X-ray spectrum of the single crystal were measured. The quality of the single crystal was further confirmed, which laid the foundation for the subsequentcharacterization of physical properties.(2) Through the measurement of the magnetic susceptibility and the analysis of the magnetic susceptibility curve and the measurement of specific heat, it is confirmed that the antiferromagnetic phase transition temperature of CuCrP2S6 is TN1=32 K, and the Curie temperature of CuVP2S6 is TC=20 K.(3) Through the measurement and analysis of the dielectric constant, specific heat, temperature dependent Raman and hysteresis loop of single crystal samples, CuVP2S6 and CuCrP2S6 are ferroelectrics at room temperature, CuCrP2S6 has structural phase transition at 173 K, and it is antiferroelectrics below 155 K. The ferroelectric transition Curie temperature of CuVP2S6 is above room temperature.(4) Through further analysis of the data of magnetic susceptibility and dielectric constant, it is found that the magnetoelectric coupling between CuMP2S6 (M = Cr, V) is weak, which conforms to the theoretical prediction that this kind of system material is the first type of multiferroic material.

二维材料 多铁性 化学气相传输法 拉曼光谱

two-dimensional material multiferroic chemical vapor transport Raman spectroscopy

中文

联合培养

南方科技大学

位龙宇. 二维层状材料CuMP2S6(M=Cr,V)多铁性质研究[D]. 深圳. 哈尔滨工业大学,2020.