Treść książki

Przejdź do opcji czytnikaPrzejdź do nawigacjiPrzejdź do informacjiPrzejdź do stopki
14
1.AnIntroductiontotheCrystalStructuresofOxidePerovskites
Figure1.1.Numberofpublicationsonperovskiteswithtime(GoogleScholar).
andDion-Jacobsonphases.Anexcellentbookthatdescribesallthevarie-
tiesofperovskite-basedcompoundsisthatbyMitchell[1].AsIconcentrate
onthecrystallographicaspectshere,Ishallnotdiscussthediferenttypes
ofpropertiesofperovskites,suchasthemultiferroicefects.Furthermore,
IreferthereadertothepapersbyWoodwardandcolleagueswhohavedone
muchworkonconsideringcationorderingandtheso-calledJahn-tellerdis-
tortionsinperovskites[2].Thelattertendtooccurmoreofteninnon-oxide
perovskitesandsoarenotdealtwithhere.
Sowhatmakestheperovskitecompoundssospecial?Tounderstand
this,oneneedstoconsiderthecrystalstructureandhowitcanbemodified
toproducediferentefects.Figure2showswhatiscalledthe“aristotype”
structure(thetermduetoH.D.Megaw)or“parent”structure.Thegeneral
formulaisABX
3,whereAandBarecationsandXisananion,usually
oxygeninmostferroelectricperovskites.
InFigure1.2,therearetwoequivalentviewsofthestructure.InFig-
ure1.2(a)theAcationisplacedontheoriginoftheunitcell,whilethe
Bcationisattheunitcellcenter.SurroundingtheBcationare6anions
forminganoctahedralarrangementaroundtheBcation.In(b)theBcation
hasbeenplacedontheunitcellorigin,thusputtingtheAcationattheunit
cellcenter.Wenowseethatthestructurecanbedescribedintermsofan