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1、β-CaBO:ANewPolymorphSynthesized47underHigh-Pressure/High-TemperatureConditionsHubertHuppertzDepartmentChemie,Ludwig-Maximilians-Universit¨atM¨unchen,Butenandtstraße513(HausD),D-81377M¨unchen,GermanyReprintrequeststoDr.H.Huppertz.E-mail:huh@cup.uni-muenchen.deZ.Naturforsch.58b,2
2、57265(2003);receivedDecember23,2002Anewoxoborateβ-CaB4O7hasbeensynthesizedunderhigh-pressure/high-temperaturecondi-tionsfromcalciumoxideandboronoxidewithaWalker-typemultianvilapparatusat7.7GPaand1100◦C.SinglecrystalX-raystructuredeterminationofβ-CaB4O7revealed:Pmn21,a=1058.4(1)
3、,b=436.9(1),c=419.4(1)pm,Z=2,R1=0.0305,wR2=0.0587(alldata).ThecompoundisisotypictotheknownoxoboratesSrB4O7,PbB4O7,andEuB4O7exhibitinganetworkstructureoflinkedBO4tetrahedra.Asaprominentfeatureofthetetrahedralnetworkanoxygenatomiscoordinatedtothreeboronatoms.Therelationofthecryst
4、alstructureofthehigh-pressurephaseβ-CaB4O7tothenormal-pressurephaseα-CaB4O7aswellastherelationtotheisotypicphasesMB4O7(M=Sr,Pb,Eu)arediscussed.TheresultsofIR-spectroscopicinvestigationsonβ-CaB4O7arealsopresented.Keywords:High-Pressure,Multianvil,β-CaB4O7,Borates,CrystalStructur
5、eIntroduction10],Ca2B6O11(2:3)[8,11],CaB2O4(1:1)[1219],Ca3B2O6(3:1)[2023],andCaB4O7(1:2)[24,25].Researchonoxoboratesprovidesdistinctiveoppor-Investigationsconcerningthebehaviourunderhigh-tunitiesforthediscoveryandidentificationofnewpressure/high-temperatureconditionswereonlyper-
6、compoundswithinterestingproperties,e.g.materialsformedonCaB2O4[18].Asstartingmaterialforforsecondharmonicgenerationorhostmaterialsforallhigh-pressurerunsMarezioetal.usedtheor-fluorescence[13].thorhombicnormalpressurephasecalciummetabo-Fromthestructuralpointofviewthereisagreatrat
7、eCaB2O4-I[15,16],inwhichallboronatomsarediversitygroundedontheabilityofborontobindtotriangularlycoordinated.Increasingthepressuretoathreeorfouroxygenatoms,formingBO3-orBO4-rangeof1.21.5GPaledtoasecondorthorhom-groupswhichcanbelinked.Recently,wefoundthatbiccalciboritephaseCaB2O4
8、-II[14],exhibitingBO3-theuseofhigh-pressureduringthesy
