硅和铈掺杂锆酸镧性质第一性原理研究

First-Principles Studies on the Properties of Si and Ce Doped Lanthanum Zirconate

锆酸镧是一类新型热障涂层材料,为重型燃气轮机、航空发动机和高超声速飞行器的高温零部件表面提供隔热降温的作用。其热膨胀系数低于现服役的钇稳定氧化锆,与粘结层的热膨胀系数不匹配,且断裂韧性比较低,导致该材料缺乏良好的增韧机制。因此,如何提高它的热膨胀系数和断裂韧性是这一领域的研究热点。应用密度泛函理论第一性原理方法对锆酸镧,及分别用硅和铈元素以一系列比例掺杂锆酸镧结构进行优化令其稳定。研究发现随Si掺杂含量增加,结构带隙展宽,弹性常数逐渐增加,结构仍保持脆性特征,断裂韧系数,平均声速、德拜温度以及最低导热系数都逐渐增加,热膨胀系数逐渐降低。而Ce取代则出现相反趋势。综合而言,与纯净锆酸镧相比,Ce掺杂有更好的弹性模量,最小导热系数和热膨胀系数,Si掺杂有更好的断裂韧性。

Lanthanum zirconate is a new type of thermal barrier coating material,which provides heat insulation and cooling effect for the surface of high temperature parts of heavy gas turbine,aero-engine and hypersonic aircraft.Its thermal expansion coefficient is lower than that of yttrium stable zirconia,which does not match the thermal expansion coefficient of the bonding layer,and the fracture toughness is relatively low,resulting in the lack of good toughening mechanism of the material.Therefore,how to improve its thermal expansion coefficient and fracture toughness is a research hotspot in this field.Using density functional theory first-principles method to optimize lanthanum zirconate with silicon and cerium elements respectively.It is found that with the increase of Si doping content,the structural band gap widens,the elastic constant gradually increases,the structure still maintains brittle characteristics,the fracture toughness coefficient,the average sound velocity,Debye temperature and the lowest thermal conductivity gradually increase,and the thermal expansion coefficient gradually decreases.The Ce substitution showed the opposite trend.In general,Ce doping has better elastic modulus,minimum thermal conductivity and thermal expansion coefficient,and better fracture toughness for Si doping than pure lanthanum zirconate doping.