The α- and β-Si3N4havetrigonal(PearsonsymbolHP28,space group P31c,No. 159)andhexagonal)HP14,P63,No. 173)structures,respectivectives4tetrahedra.theycanberegardedasconsistingoflayersofsiliconandnitrogenatomsinthesequenceabab..orabcdabcd..inβ-si3N4 and α-Si3N4,respectively.theablayeristhesameintheαandβphases,andtheCDlayerintheαphaseisrelatedtoabbyac-glideplane.thesi3N4 tetrahedra in β-Si3N4areinterconnectedinsuchawaythattunnelsareformed, runningparallelwiththecaxisoftheunitcell.duetothec-glideplanethatrelatesabtoCD,theαstructurecontainscavitiesinsteadoftununing3N4isoftendesignatedascmodificationintheliterature, Inanalogywiththecubicmodificationofboronnitride(c-bn)))。 .ithasaspinel-typestructureinwhichtwosiliconatomseachcoordinatesixNitrogenatomsoctahedrally,andonesiliconatomcoordinatesfinates
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