High-throughput Calculation And Study Of Sb₂Te₃ Phase-change Memory Materials In Solid Solution Of Sb-Te And Noble Metals

With the increasement of global data amount,the traditional storage system(ie,Flash memory,FLASH)fails to meet the requirements of fast,high density and low power consumption in the big data era,due to its physical limits.Phase-change random access memory(PCRAM)is regarded as the leading candidate for next-generation memory hierarchy,because of its simple structure,high speed,low power consumption and long service life.The core of PCRAM is phase change materials(PCM),which is based on the chalcogenides.Compared with most PCM,Sb-Te alloys have attracted the people's attention,due to its fast crystallization rate.However,the poor thermal stability of amorphous states of Sb-Te alloys is the main obstacle that keeps it away the practical applications.In addition,the reported works on Sb-Te alloys are mainly focused on sever intermetallic Sb_mTe_n compounds with fixed Sb/Te atom ratio,and are insufficient to explain the relationship between phase change properties and components of Sb-Te alloys.Therefore,the Sb_1-xTe_x solid solutions as well as several typical intermetallic Sb_mTe_n compounds were studied by High-throughput calculations and ab-initio molecular dynamics,in this thesis.On this basis,the modification of Sb-Te alloys was studied:the feasibility of NM-Sb-Te solid solutions(NM=Ru?Rh?Pd?Ag?Os?Ir?Pt?Au),as PCM applications was discussed,and the effect of NM elements on the thermal stability of Sb-Te alloys at amorphous states was investigated.Based on above,a material database for NM-Sb-Te alloys should be established to explore the material genes of NM-Sb-Te alloys.It is expected that the mechanism of Sb-Te alloys,as well as the feasibility and optimal type NM-Sb-Te solid solutions,as PCM application could be investigated.Based on this,establish a functional NM-Sb-Te phase change material database,in order to prepare for further research and machine learning.The main research contents are as fllows:(1)In order to deeply understand the intrinsic mechanism of Sb-Te alloys in PCM field and explore the best candidate material,the energy,structure,stability and electronic structure of Sb-Te alloys were systematically studied by theoretical calculation method.The results show that:the most stable structure form of Sb-Te alloys is layered structure;the energy convex hull of Sb-Te alloys is consisted of pure Sb,pure Te and Sb₁₆Te₃,Sb Te and Sb₂Te₃ intermetallic compounds;Sb_1-xTe_x solid solutions is the metastable phase of Sb-Te alloys,but the decomposition of solid solutions can be inhibited by increasing the temperature properly;the differences between crystalline states and amorphous states of Sb-Te alloys is relatively small in Sb-rich region and Te-rich region;the electronic structure of the Sb-Te alloys in the middle region is obviously different from that in the amorphous region.Combined with the calculation results of energy,structure,stability and electronic structure,it is believed that the best solid solubilities of Sb-Te alloys for PCM is in the range of 0.4<x<0.6.(2)In order to investigate the effect and mechanism of NM elements on Sb-Te alloys,the Sb₂(Te_1-xNM_x)₃ and(Sb_1-xNM_x)₂Te₃ solid solutions was chosen to study.The energy,crystal structure,stability,electronic structure and amorphous structure of the two kinds solid solutions were calculated and compared.The results show that:the structural stability for both solid solutions is poor when the solid solubilities x<0.167;the layered structure of Sb₂(Te_1-xNM_x)₃ solid solutions will be destroyed with the increasement of solid solubility of NM elements(x>0.889 or x>0.778);the layered structure of(Sb_1-xNM_x)₂Te₃ solid solutions is maintained in the whole solid solubility range;the disordered degree of Sb₂(Te_1-xNM_x)₃ solid solutions is limited;and the contribution of NM-nd states is much stronger than that of Sb-5p states and Te-5p states,indicating a more NM elements behavior for the solid solutions;the disordered degree of(Sb_1-xNM_x)₂Te₃ solid solutions is higher,and the electronic structure is contributed by the hybridized states of NM-nd,Sb-5p and Te-5p states;when NM=Pd?Ag?Pt?Au,the differences between crystalline states and amorphous states for both solid solutions are relatively small,indicating the above elements are not suitable for PCM application.Considering the results of energy,crystal structure,amorphous structure and electronic structure,it is believed that the(Sb_1-xNM_x)₂Te₃ solid solutions is more suitable for PCM application,and the best NM elements are Os and Ir.(3)Based on the research results of Sb-Te alloys and Sb₂(Te_1-xNM_x)₃ and(Sb_1-xNM_x)₂Te₃ solid solutions,the database of NM-Sb-Te phase change materials was developed and constructed by using browser/server architecture.In order to realize the accurate query of data,the multi condition query function was built into database system;the dynamic maintenance of the database was realized;a simple interface and intuitive operation logic was set;and the database system is ready to further development;1,318 data records are stored in the database,generating 23,724data points.The innovation of this thesis are as follows:the theoretical calculation of Sb_1-xTe_x solid solutions system is carried out for the first time.The crystal structure,electronic structure and amorphous structure of Sb-Te alloys were studied,and the solid solubility range(0.4<x<0.6)of Sb-Te alloys suitable for PCM application was predicted.Through the investigation of Sb₂(Te_1-xNM_x)₃ and(Sb_1-xNM_x)₂Te₃ solid solutions,the stable atom site and suitable solid solution types for PCM application were found;the NM-Sb-Te phase change materials database was established,which complied with the material genome project and provides the guidance for the subsequen study about NM-Sb-Te alloys...