LaMgAl11O19(LMA),characterized by high melting point,low density and thermal conductivity as well as good infrared emissivity,is regarded as a potential candidate for the thermal protection of hyper-sonic vehicles.Nevertheless,the unsatisfied phase stability at high temperature results in declining of the emissivity below 6 μm,which limits the extensive applications of LaMgAl11O19.In order to overcome this obstacle,three dense bulk high-entropy ceramics,(La0.2Nd0.2Gd0.2Sm0.2Pr0.2)MgAl11O19(HE LMA-1),(La0.2Nd0.2Gd0.2Sm0.2Dy0.2)Mg Al11O19(HE LMA-2)and La(Mg0.2Fe0.2Co0.2Ni0.2Zn0.2)Al11O19(HE LMA-3),were designed and successfully prepared through solid state reaction at 1700℃for 4 h in one step.XRD analyses show that the phase compositions of HE LMA-1,HE LMA-2 and HE LMA-3 are single-phase solid solutions with the relative density of 95.61％,95.49％and 94.31％,respectively.Heat treatment experiments demonstrate that the phase composition of HE LMA-1 remains a single phase after high-temperature heating,while second phase appears in other two samples.The stability of HE LMA-1 is attributed to small average size difference δ(～4％)of constitute elements.Intriguingly,the average emissivity of HE LMA-1 in the range of 3-6 μm reaches 0.9,which is significantly higher than that of LMA and other two HE LMA samples.The emissivity of all samples remains above 0.95 from 6 to 10 μm.In the far infrared region(10-14 μm),although the emissivity of these specimens decreases slightly,it still exceeds 0.85.The UV-Vis absorption spectra indicate that the formation of many discrete impurity energy levels with small intervals in HE LMA-1 promotes the f electrons to transit between adjacent impurity energy levels and conduction band,which enhances the infrared emission of HE LMA-1 below 6 μm.In a word,with improved phase stability and thermal emissivity in infrared range,high-entropy REMgAl11O19,especially(La0.2Nd0.2Gd0.2Sm0.2Pr0.2)MgAl11O19(HE LMA-1),is a promising candidate in thermal protection coatings of hypersonic vehicles.

Haolin Zhu;Ling Liu;Huimin Xiang;Fu-Zhi Dai;Xiaohui Wang;Zhuang Ma;Yanbo Liu;Yanchun Zhou

School of Materials Science and Engineering,Beijing Institute of Technology,Beijing 100081,China;Science and Technology on Advanced Functional Composite Laboratory,Aerospace Research Institute of Materials&Processing Technology,Beijing 100076,China;National Key Laboratory of Science and Technology on Materials under Shock and Impact,Beijing 100081,China;Beijing Institute of Technology Chongqing Innovation Center,Chongqing 401120,China;Shenyang National Laboratory for Materials Science,Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China

材料科学技术（英文版）

[1]Haolin Zhu;Ling Liu;Huimin Xiang;Fu-Zhi Dai;Xiaohui Wang;Zhuang Ma;Yanbo Liu;Yanchun Zhou-.Improved thermal stability and infrared emissivity of high-entropy REMgAl11O19 and LaMAl11O19(RE=La,Nd,Gd,Sm,Pr,Dy;M=Mg,Fe,Co,Ni,Zn))[J].材料科学技术（英文版）,2022(09):131-144

REMgAl11O19,LaMAl11O19,2Nd0,2Pr0,MgAl11O19,2Dy0,Al11O19

Improved,thermal,stability,infrared,emissivity,entropy,LaMgAl11O19,LMA,characterized,by,melting,point,density,conductivity,well,good,regarded,potential,candidate,protection,vehicles,Nevertheless,unsatisfied,phase,temperature,results,declining,below,which,limits,extensive,applications,order,overcome,this,obstacle,three,dense,bulk,ceramics,La0,2Gd0,2Sm0,HE,Mg0,2Fe0,2Co0,2Ni0,2Zn0,were,designed,successfully,prepared,through,solid,state,reaction,one,step,analyses,show,that,compositions,single,solutions,relative,respectively,Heat,treatment,experiments,demonstrate,remains,after,heating,while,second,appears,other,two,samples,attributed,small,average,size,difference,constitute,elements,Intriguingly,range,reaches,significantly,higher,than,above,from,far,region,although,these,specimens,decreases,slightly,still,exceeds,UV,Vis,absorption,spectra,indicate,formation,many,discrete,impurity,energy,levels,intervals,promotes,electrons,transit,between,adjacent,conduction,band,enhances,emission,word,improved,especially,promising,coatings,hypersonic

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