Crystal Structure And Magnetic Properties Of Lamellar Carbides R(Al_1-xSi_x)₃C₃ （R=Gd,Tb,Dy,Ho,Er,Tm,x=0.1,0.2,0.25）

The new layered carbides with(TC)n(Al3C2)structure have relatively rich composition,flexible stacking units and the possibility of selective etching.They have become new members of layered carbides family with great application potential and research value.The introduction of monatomic layer magnetic elements,such as rare earth elements,into new layered carbide crystals is conducive to the extension of these materials to optical and magnetic fields.Rare earth layered carbide RAl3C3,as a member of new layered carbide ceramic(TC)nAl3C2,has broad research prospects in high temperature structural materials,electromagnetic shielding materials,optoelectronic materials,electrode materials and other application fields.At present,the research direction of rare earth layered carbides mostly focuses on theoretical simulation,structure,electronic,mechanical and optical properties.There is no report on the synthesis of solid solution by partial replacement of Al position.The change of crystal structure and magnetic properties caused by solid solution is of great significance to understand the basic structure and properties of this kind of materials.Therefore,the crystal structure and magnetic properties of rare earth layered carbide were studied by adding and adjusting the proportion of solid solution elements.In this paper,a series of quaternary carbides R(Al1-xSix)3C3(x=0.1,0.2,0.25)were obtained by using ternary layered ceramics RAl3C3(R=Gd,Tb,Dy,Ho,Er,Tm)as matrix and substituting Al with different contents of Si.Their microstructure was studied by XRD and their magnetic properties were measured by VSM.(1)R(Al1-xSix)3C3 layered carbide solid solution can be successfully synthesized by pressureless sintering.In the temperature range of 1300℃ to 1600℃,Si can replace Al in RAl3C3 to form R(Al1-xSix)3C3 layered carbide solid solution.At the same preparation temperature,with the increase of Si substitution,the impurity content in the synthesized products also increases.The impurity phases in the prepared R(Al1-xSir)3C3 layered carbide materials mainly include Si,C and SiC.Under the condition of 1500℃ for 1 hour,the saturated solid solution content of Si element which can form layered carbide solid solution is less than 30%.(2)The diffraction peaks of the sintered samples of layered carbide ceramics with different contents of Si replacing Al are basically the same as those of the corresponding ternary carbides,which indicates that the quaternary carbides R(AI1-xAix)3C3 with different contents of Si replacing Al do not change the crystal structure,but still maintain the crystal structure of ternary layered carbides,that is,hexagonal crystal system with P63/mmc space group.However,with the solid solution of Si element,the lattice parameters of the crystal change to a certain extent.The lattice constant a of Dy(Al1-xSix)3C3 decreases from 3.41 ? to 3.40 ?,and the lattice constant c decreases from 17.24 ? to 17.21 A when the Si substitution amount x increases from 0.1 to 0.25.It is proved that the substitution of Si for Al in the synthesis of R(Al1-xSix)3C3 makes the cell smaller.(3)All the samples of R(Al1-xSix)3C3(x=0.1,0.2,0.25)are paramagnetic at high temperature.The five samples of R=Gd,Tb3 Dy,Ho,Er will have magnetic phase transition with the change of temperature at the field strength of 0.1 T,while the samples of R=Tm show a single paramagnetic phase at different temperatures.The paramagnetic Curie temperature obtained by fitting the paramagnetic part of χ-1-T according to the Curie-Weiss law shows that the paramagnetic Curie temperature of R(Al1-xSix)3C3 decreases with the increase of Si substitution.(4)The effective magnetic moments of Si substituted samples are close to the theoretical values of rare earth free ions,but smaller,indicating that the magnetic properties of all samplesof R(Al1-xSix)3C3(x=0.1,0.2,0.25,R=Gd,Tb,Dy,Ho,Er,Tm)are mainly from+3 valent rare earth ions.The introduction of Si can cause the reduction of+3 valent rare earth ions and the formation of antiferromagnetic and other magnetic phases makes the effective magnetic moment of the sample smaller than the theoretical value.