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1、12884J.Phys.Chem.B2006,110,12884-12889Two-StageMeltingofAu-PdNanoparticlesSergioJ.MejõÂa-Rosales,CarlosFernaÂndez-Navarro,andEduardoPeÂrez-TijerinaFacultaddeCienciasFõÂsico-MatemaÂticas,UniVersidadAutoÂnomadeNueVoLeoÂn,SanNicolaÂsdelosGarza,NueVoLeoÂn,MeÂxico66450JuanM
2、artõÂnMontejano-CarrizalesInstitutodeFõÂsica,UniVersidadAutoÂnomadeSanLuisPotosõÂ,SanLuisPotosõÂ,S.L.P.,MeÂxico78000MiguelJoseÂ-YacamaÂn*ChemicalEngineeringDepartmentandTexasAdVancedMaterialsCenter,TheUniVersityofTexasatAustin,Austin,Texas78712.ReceiVed:March9,2006;InF
3、inalForm:April26,2006Severalseriesofmoleculardynamicsrunswereperformedtosimulatethemeltingtransitionofbimetalliccuboctahedralnanoparticlesofgold-palladiumatdifferentrelativeconcentrationstostudytheirstructuralpropertiesbefore,in,andafterthetransition.Thesimulationswere
4、madeinthecanonicalensemble,eachseriescoveringarangeoftemperaturesfrom300to980K,usingtheRafii-TabarversionoftheSuttonandCheninteratomicpotentialformetallicalloys.Wefoundthatthemeltingtransitiontemperaturehasastrongdependenceontherelativeconcentrationsoftheatomicspecies.
5、Wealsofoundthat,previoustothemeltingtransition,theouterlayerofthenanoparticlegetsdisorderedinwhatcanbethoughtasapremeltingstage,whereAuatomsnearthesurfacemigratetothesurfaceandremainthereaftertheparticlemeltsasawhole.ThemeltingofthesurfacebelowTmisconsistentwithstudies
6、oftheinteractionofaTEMelectronbeamwithAuandAu-Pdnanoparticles.1.Introductioninthemelting-freezingcycle.Clevelandetal.found,alsobytheuseofMD,thattruncatedoctahedraofAu459anddecahedraNanoparticlesaregoodcatalystsbecauseoftheirhigherofAu146undergoastructuraltransitiontoic
7、osahedrabeforenumberofsurfaceatomsincomparisontobulkmaterials.Inmeltingtakesplace.7InanotherMDstudy,8thepremeltingofparticular,thereisagrowinginterestintransitionmetalalloystheAusurfaceisconfirmed,anditisfoundthatthemeltingascatalysts,mainlybecausethesematerialsshowaco
8、nsiderable1temperatureoftheAunanoparticlesstronglydependsontheimprovementinefficiencywhencomparedtopuremetals.Thesize
