Ferroelastic phase transitions.pdf

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1、phasetransitionsActaCrystallographicaSectionAFerroelasticphasetransitions:structureandmicro-FoundationsofCrystallographystructureISSN0108-7673aaa,bEkhardK.H.Salje,*StuartA.HaywardandWilliamT.LeeReceived3May2004Accepted16August2004aDepartmentofEarthSciences,UniversityofCambridge,Do

2、wningStreet,CambridgeCB23EQ,bEngland,andMineralogisch-PetrographischesInstitut,UniversitaÈtHamburg,Germany.Corre-spondencee-mail:es10002@esc.cam.ac.ukLandau-typetheoriesdescribetheobservedbehaviourofphasetransitionsinferroelasticandco-elasticmineralsandmaterialswithahighdegreeofac

3、curacy.Inthisreview,thederivationoftheLandaupotentialG=1A[coth(/T)ÿ2SScoth(/T)]Q2+1BQ4+...isderivedasasolutionofthegeneral4model.SC4Thecouplingbetweentheorderparameterandspontaneousstrainofaphasetransitionbringsthebehaviourofmanyphasetransitionstothemean-®eldlimit,evenwhenthea

4、tomisticmechanismofthetransitionisspin-like.Straincouplingisalsoacommonmechanismforthecouplingbetweenmultipleorderparametersinasinglesystem.Aswellaschangesonthecrystalstructurescale,phasetransitionsmodifythemicrostructureofmaterials,leadingtoanomalousmesoscopicfeaturesatdomainboun

5、daries.ThemesostructureofadomainwallisstudiedexperimentallyusingX-raydiffraction,andinterpretedtheoreticallyusingGinzburg±Landautheory.Oneimportantconsequenceoftwinmeso-structuresistheirmodi®edtransportpropertiesrelativetothebulk.Domainwallmotionalsoprovidesamechanismforsuperelast

6、icbehaviourinferroelastics.Atsurfaces,therelaxationsthatoccurcanbedescribedintermsoforderparametersandLandautheory.Thisleadstoanexponentialpro®leofsurfacerelaxations.Thisinturnleadstoanexponentialinteractionenergybetweensurfaces,whichcan,iflargeenough,destabilizesymmetricalmorphol

7、ogiesinfavourofaplateletmorphology.Surfacerelaxationsmayalsoaffectthebehaviouroftwinwallsastheyintersectsurfaces,sincethesurfacerelaxationmayleadtoanincompatibilityofthetwodomainsatthesurface,generatinglargestrainsattherelaxation.Landautheorymayalsobeextendedtodescribethekineticso

8、fphasetransitions.Time-dependentL