Synthesis And Characterization Of Hg-based High Temperature Superconducting Single Crystal And Cubic B-C-N Compound

Nowdays, high temperature superconductors and hard materials both attract lotsof attentions, which can be widely applied in aerospace, communication andmechanical engineering etc. This thesis contains two parts. In the first part, we focuson the synthesis and properties of mercury based high temperature cupratesuperconductors，which is the primary part of the thesis; in the another part, weexplore the synthesis of cubic B-C-N compound.Since high temperature cuprate superconductor with Tc=35K have been obtainedin1986, it have been intensively studied in the field of superconductors.Unfortunately, the mechanism of the high temperature superconductor is stillconfusing until now. Because of the anisotropy of superconductors, the single crystalis needed to study the properties of high temperature superconductors. Mecury basedcuprate superconductor not only have the highest Tcin all the superconductors, butalso have a simple tetragonal crystal structure, so it is a ideal model to explore themechanism of high temperature superconductors. However, it is hard to get sizableand high quanlity single crystals. In this thesis, we refine the synthesis routing ofHg1201single crystal and the operate detail, noteworthy, using our synthesis andanneal method, we can not only make the oxygen in the sample homogenous but alsoadjust the hole doped concentration which is more proficient than before. Base on oureffort, we expand our research to study the charge density wave (CDW) in theHg1201single crystal by the measurement of RXD and RIXS. Further more, we usetwo step method, which is similar to the synthesis of Hg1201, and successfully obtain Hg1212single crystal. Through the refinement of the procedure of the synthesis, wecan get large size and high quanlity Hg1212single crystals. Because of the anisotropyof mercury based high temperature superconductors, only large size single crystalscan get accurately results through characterizations. So the micrometer scale Hg1212single crystal is essential for the following work. The typical synthesis is followed:first, the mixture of Ba(NO3)2and CuO is heated to get the precursor, then theprecursor is mixed with CaO and HgO in the glove box, finally, the mixture isencapsulated into the quartz tube and heated with certain heating cycles. After thesynthesis, we anneal the samples of Hg1212single crystals. Through characterize thethe magnetic susceptibility of the annealed samples, We find that the Tconsetof theannealed Hg1212single crystal is about123K. The result we obtained is very close tothe Tconsetof the optimize doped Hg1212, it can be use for following measurements.Furthermore, it is the base to get underdoped and over doped Hg1201single crystal.CDW can be found in the superconducting and pseudogap phase. Because CDWcoexists and competes with the superconducting state, it plays an important role forunderstanding the mechanism of superconductivity. In this thesis, we characterizedthe Hg1201single crystal (p≈0.09, Tc=72K) with RXD and RIXS in order to explorethe CDW. We measure resonance X-ray diffraction around the Cu L-edge energy.Without magnetic field, the correlations and competition of the CDW withsuperconductive is weaker comparing with results of YBCO. However, we didobserve the CDW in Hg1201. We find that the short range CDW and Fermi-liquidbehavior simultaneously appear at the same temperature around200K. During theCDW measurements, we first study the [H, K, L] in momentum space and finally wedecided to measure the CDW at [H,0, L] where L is correspond to H. Subsequent, wescan the energy when the value of H is fixed. We find that there is an energyabsorption which is due to charge density wave in the quasi-elastic peaks. Then, wescan the momentum with the fixed energy, we find that the charge density wave:HCDW=0.276(5) r.l.u.,2κ=0.058(9) r.l.u.（RXD）；HCDW=0.280(5) r.l.u.，2κ=0.071(3)r.l.u.（RIXS）. At last, we scan the temperature when the energy and momentum arefixed, the results show that the CDW of Hg1201appear around200K and theintensity is increasing with the temperature reduce until72K, then steadily insuperconducting state.During the period we study the high temperature superconductors, we simultaneously explore the synthesis of the cubic B-C-N compound. Because thecubic B-C-N is hopeful both having high hardness as diamond and high chemicalstable as cubic BN, it’s attract lots of attentions. But in the previous work, thesynthesis condition of cubic B-C-N is always hard to achieve. In this thesis, we viatwo step method suscellfully get the cubic B-C-N sample. The typical synthesisprocedure is followed: firstly, the mixture of graphite and h-BN is ball milled asprecursor, then we mingle the precursor with catalyst and deal the mixture with highpressure (12GPa) and high temperature (1500oC). Through the characterization ofthe sample we obtained, the structure of it is established to cubic boron nitride type inwhich the boron atoms are partially substituted by the carbon atoms. Through ballmilling and using the catalyst, we lower the synthesis condition of cubic B-C-N. Thestructure of our sample is also very interesting.