Structure Exploration And Physical Property Characterization Of Transition Metal Low-dimensional Nitrides And Carbides

Since the discovery of superconductivity,people's enthusiasm for exploring new superconducting materials has only increased,and various types of superconductors have been discovered one after another.The parent superconductor La Fe As O of the ZrCuSiAs-type structure discovered in 2008 is composed of a fluorite-type structure[La₂O₂]²⁺layer and an inverse fluorite-type structure[Fe₂As₂]^2-layer,and exhibits antiferromagnetic spin density waves at low temperatures.Subsequent studies have found that the substitution of electron type,hole type,and part of the same valence elements can suppress the antiferromagnetic ground state of the system and induce superconductivity.It shows that this type of structure has strong adaptability for element substitution.In 2016,our group first synthesized a new type of ZrCuSiAs compound ThFeAsN through physical property measurement and showed that it can exhibit 30 K superconductivity without doping,and does not have the antiferromagnetic and spin density wave states that were common in the past.Subsequent studies have shown that the reason for the enhancement of superconductivity lies in the c-direction chemical pressure.In addition to the ZrCuSiAs-type structure,we have noticed that all known families of quasi-two-dimensional superconductors have the following characteristics:First,from the structural point of view,the conductive layer does not exist in isolation.A series of compounds can always be found isomorphic with the conductive layer of known superconductors.Second,in all conductive layers of the same structure,there are always multiple conductive layers that can bear superconductivity.Based on the above-mentioned empirical rules,we analogized and extended the structure of a type of superconductor based on the Ti₂Pn₂O conductive layer,and discovered a superconductor with a Mo₂Si₂C conductive layer.Based on the above findings,the main contents of this paper are as follows:Firstly,We synthesized a new quaternary compound ThMo₂Si₂C by arc,which belongs to the tetragonal structure of CeCr₂Si₂C type,and its unit cell parameters are a=4.2296(?)and c=5.3571(?).The refinement of the structure based on X-ray diffraction showed that there is a Si-Si covalent bond between the conductive layers.The resistance and magnetic susceptibility measurements of the compound show that the material is a Pauli paramagnetic at high temperatures.When the temperature drops below 2.2 K,the material undergoes a superconducting phase transition.The measurement of specific heat shows that the jump of specific heat caused by superconductivity becomes?C/?_nT=0.98.In addition,we also carried out a series of physical property measurements to characterize the material's superconducting lower critical field H_c1,upper critical magnetic field H_c2,superconducting coherence length?,London penetration depth?,and superconducting energy gap.Secondly,Based on the previous studies in ThFeAsN and ThNiAsN,we speculate that there is a chemical pressure in the c-axis direction in all compounds containing a Th₂N₂layer,and this pressure will have a significant impact on physical properties.Based on this speculation,we have previously synthesized a series of new Mn-based compounds ThMnPN and ThMnAs N.This article continues to extend the experiment and first synthesized a layered compound ThMnSbN based on Mn.This article analyzes the crystal structure of this new manganese-based compound in detail and confirms that there is indeed a similar chemical pressure in the c-direction.In addition,a series of physical property measurements also show that this built-in chemical pressure significantly improves the traveling characteristics of d-orbital electrons and has an impact on the antiferromagnetic ground state of the system.