Study On Defect Energetics And Thermal Properties Of Ln₃TaO₇?Ln=La-Ho? Weberites By Firstprinciples Calculations

The safe disposal of high-level radioactive waste is an effective guarantee for the safe and sustainable development of nuclear energy.Based on this problem,ceramic solidification has been widely concerned by researchers in related fields.Fluorite derived structure is one of the most potential foundation materials of high radioactive waste.A₂B₂O₇ pyrochlore is one of the derivatives of fluorite,Due to its excellent irradiation resistance,mechanical stability and thermal stability,it has become a research hotspot in the field of ceramic solidification.Previous studies have shown that pyrochlores undergo ordered-disordered phase transition under irradiation.The latest research has declared that obvious local structural ordering exists in disordered pyrochlores,which can be described as weberite-type superstructure.Therefore,the study of the amorphous mechanism of ceramic oxides should not only take into account its macroscopic performance,but also the role of its microstructure in it.In addition,attention should also be paid to the weberite-structure and related compounds.Ln₃TaO₇?Ln=La,Pr,Nd;Sm-Ho?is one of the derivatives of fluorite.Due to the foundation materials are in high irradiation,high temperature and complex crustal stress environment,Therefore,the irradiation resistance ability,thermal stability and mechanical stability of materials have been put forward stringent requirements.Based on the previous research,the amorphous resistance ability,mechanical stability and thermal stability of these compounds were evaluated by calculating defect formation energy,mechanical and thermal properties of the series of compounds.The main conclusions of this paper are as follows:1.Calculation of defect energetics show that the cation antisite defect formation energy of Ln₃TaO₇?Ln=La,Pr,Nd;Sm-Ho?is all small,Therefore,we guess that this series of materials have excellent irradiation resistance ability.2.The results of mechanical properties calculation showed that the poisson ratio of Ho₃TaO₇ was the smallest and the hardness of it was the largest,indicating that the mechanical stability of Ho₃TaO₇ was the best in this series of materials.3.The calculation results of thermal properties show that the thermal expansion coefficient of this series materials is very small(order of magnitude is 10^-6),indicating that the volume shrinkage or expansion are small.The heat capacity of Ho₃TaO₇ was the highest.The entropy increasing trend of Ho₃TaO₇ was consistent with that of other compounds and the entropy increase of Ho₃TaO₇ is the largest,indicating it has the maximum degree of structural disorder.Considering the irradiation resistance ability,thermal stability and mechanical stability of this series materials together,we believe that Ho₃TaO₇ is the most potential high-radioactive waste foundation material in this series materials.