铋层状化合物的结构与铁电、介电性能

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1、浙江大学博士学位论文AbstractBismuthlayer-structuredcompoundsareafamilyofferroelectficsusuallypossessinghi出Curietemperature．Thesecompoundsplayanimportantroleintheintegratedferroelectricsindustry．Inthisthesis，thelanthanidesubstitutionWaScarriedoutinsometypicalbi

2、smuthlayer-structuredcompoundsandthevariationofstructure，theferroelectricanddielclctricpropertieswereinvestigated．Then，therelationbetweenthestructurestabilityandtheaverageradiusofA—sitecationsWasdiscussed．ThediffusephasetransitionsofsomeBa-basedbismu

3、thlayer-structuredcompoundswerealsodescribedandanalyzed．WithLa3+substitution，Bi4一xLaxTi3012underwentanevolutionfromorthorhombictotetragonalstructure．Accordingly,ferroelectricityinBi4-xLaxTi3012wasimpairedandfinallydisappeared．Bi4．xLaxTi30j2exhibitedr

4、elaxorbehaviorsatx=1．2．Whenxexceeded1．2．Bi4．xLaxTi3012wasparaelectricatroomtemperature．Dielectricceramicswithdielectricconstantshigherthan125andlowtan5valuesintheorderof10。4wereattainedwhenx>1．2．TheauthorsuggestedthatLa3+substitutionhavelittleeffecto

5、nthelong—rangeCoulombforcesbutenhancetheshort·rangerepellingforcesinfavorofthestabilityofparaelectricstructure．Thismaybethereasoilfortheimpairmentofferroelec伍cityinBi4．xLaxTl30t2．Similarresultswereob诅inedinLa3+substitutedSrBi4Th015．Solidsolutionsform

6、edwithintherangeof05x茎1．2inSrBi4一xLaxTi4015．CurietemperaturewassignificantlyloweredwithLa3+substitution．Thephasetransitionbecamediffusedandrelaxorbehaviorswerefoundforx三O．8．ThediffusiondegreeofthephasetransitionwasenhancedwithincreasingX，Thestructure

7、refinementsofSrBi4一xLaxTi40t5atx=1．0revealedthattheexternalandinternaloxygenoctahedraweredifferentbothinthetiltingaroundthecrystallographicaxisandinthedeviationofTi4+fromtheequilibriumposition．Furthermore．therewasacationdisorderattheperovskiteA‘sitea

8、ndthecationsitein(Bi202)2+layer．Thiswasbelievedtoberesponsibleforthediffusionofthephasetransition．Tofurthercleartherelationshipbetweenthefactorscontributingtothe铋层状化合物的结构与铁电、介电性能ferroelectricityinbismuthlayer-structuredcompounds，smallNd”wasusedtorepl