Synthesis,formation mechanism,and intrinsic physical properties of several As/P-containing MAX phases  

作　　者：Hongxiang Chen Sheng Li Jun Deng Zhilong Zhang Jianeng Huang Fa Chang Li Huang Shixuan Du Pinqiang Dai 

机构地区：[1]School of Materials Science and Engineering,Fujian University of Technology,Fuzhou 350118,China [2]Institute of Physics&University of Chinese Academy of Sciences,Chinese Academy of Sciences,Beijing 100190,China [3]Fujian Provincial Key Laboratory of Advanced Materials Processing and Application,Fuzhou 350118,China [4]Center for Advanced Energy and Functional Materials,Fujian University of Technology,Fuzhou 350118,China [5]Songshan Lake Materials Laboratory,Dongguan 523808,China [6]CAS Key Laboratory of Vacuum Physics,Beijing 100049,China

出　　处：《Journal of Materials Science & Technology》2023年第2期23-31,共9页材料科学技术（英文版）

基　　金：supported by the National Science Foundation for Young Scientists of China(No.51902055);the Natural Science Foundation of Fujian Province(Nos.2021J011077,2021J05224,and 2020J01898).

摘　　要：321 phases are an atypical series of MAX phases,in which A=As/P,with superior elastic properties,fea-turing in the MA-triangular-prism bilayers in the crystal structure.Until now,besides Nb 3 As 2 C,the pure phases of the other 321 compounds have not been realized,hampering the study of their intrinsic prop-erties.Here,molten-salt sintering(MSS)and solid-state synthesis(SSS)were applied to synthesize As/P-containing 321 phases and 211 phases.Analyzing the phase composition of the end-product via multiple-phase Rietveld refinement,we found that MSS can effectively improve the purity of P-containing MAX phases,with the phase content up to 99%in Nb_(3)P_(2)C and 75.4(5)%in Nb 2 PC.In contrast,MSS performed poorly on As-containing MAX phases,only 8.9(4)%for Nb 3 As 2 C and 64(2)%for Nb 2 AsC,as opposed to the pure phases obtained by SSS.The experimental analyses combined with first-principles calculations reveal that the dominant formation route of Nb_(3)P_(2)C is through NbP+Nb+C→Nb_(3)P_(2)C.Moreover,we found that the benefits of MSS on P-containing MAX phases are on the facilitation of three consid-ered chemical reaction routes,especially on Nb 2 PC+NbP→Nb_(3)P_(2)C.Furthermore,the intrinsic physical properties and Fermi surface topology of two 321 phases consisting of electron,hole,and open orbits are revealed theoretically and experimentally,in which the electron carriers are dominant in electrical trans-port.The feasible synthesis methods and the formation mechanism are instructive to obtain high-purity As/P-containing MAX phases and explore new MAX phases.Meanwhile,the intrinsic physical properties will give great support for future applications on 321 phases.

关 键 词：MAX phase Molten-salt synthesis Chemical reaction route Metallic ceramics Formation mechanism Quasi-harmonic approximation 

分 类 号：TG113[金属学及工艺—物理冶金]