| In transition metal compounds with low dimensional structure, superconductivity, magnetism,charge density waves and even many kinds of ordered states could coexist and compete with each other. The study of the relations between these ordered states and the further modulation of the ordered states has become a hot topic in condensed matter physics for many years. From the experimental experience, in addition to the important factors such as the concentration of the carrier and the electronic structure, the sintering temperature, composition segregation, defects and the degree of the crystallization will also affect the superconducting transition temperature. The study of the effects of these factors on superconductivity is of great importance in searching for new high temperature superconductors and the clarification of the mechanism of superconductivity. In this thesis, the relationship between the sample preparation conditions and the superconducting transition temperature in LaRu2As2 with 122 phase structure is studied. Also we study the change of the properties of the ground state caused by Te doping on Se site in the TiSe2 system.The thesis has four chapters. The first chapter is the introduction. First of all, the history and background of superconductivity are briefly introduced. Then, a brief introduction to the most popular iron-based superconductors and 122 iron-based superconductors is given. Furthermore, the study on the other 122-type structure systems is introduced. The introduction chapter also introduces a large family of the superconductivity: transition metal chalcogenide(TMD) compounds, including some of the rich physical properties of TMD. The second chapter is the about the main experimental methods.The sample preparing method and the measurement methods are described in detail, including the X ray diffraction measurement, resistivity measurements, SQUID measurements and the specific heat measurement.In the third chapter, the relationship between the preparation conditions and superconductivity of LaRu2AS2 superconductor is studied. By studying the relation between the physical quantities such as lattice parameters and the residual resistivity and the sintering temperature of the sample, we speculate that the superconducting transition temperature is significantly affected by the sintering temperature of the sample, mainly due to the different crystallization temperature and the disordering degree caused by different sintering temperatures. Between 950℃ and 1100℃, every 50 degrees, we fired a total of 4 samples. From the transport properties, the lower the sintering temperature, although the time required for the formation of the phase is longer, but the value ofp5K is smaller and the value of RRR is higher. It means that the better of quality of the samples, the higher the superconducting transition temperature. Our research shows that the lower sintering temperature of the sample can lead to higher quality of the samples, and is also more favorable for the emergence of superconductivity.In the fourth chaper, we mainly studied the change of the physical properties of the Ti (Se1-xTex)2 system induced by Te doping. Although the Te element can not be completely doped into the system according to the nominal component. But the actual doping ratio is in proportion to the nominal doping ratio. When the nominal doping ratio is greater than 0.03, the suppression of CDW becomes remarkable. When the. Te consentrations is greater than 0.05, CDW has been completely suppressed.The samples, behave more metallic, but superconductivity was not observed above 1.8K. Further studies are needed to determine whether superconductivity will occur in the Te doped Ti (Se1-xTex)2. |
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