X.M.Min
,
C.W.Nan and K.F.Cai National Key Laboratory of Advanced Technology for Materials Synthesis and Processing
,
Wuhan University ofTechnology
,
Wuhan 430070
,
China
金属学报(英文版)
Thecorrelation between composition, structure, chemical bond, and thermoelectric proper tiesof Si doped boroncarbidesisstudied using SCF DV Xαmethod. Thecalculationsshow that Siatom firstlysubstitutes Bor Catomson theend of boron carbidechain, then may occupyinterstitialsites when Siis dopedin boron carbide, anditisdifficultfor SitosubstituteBor Catom in thecenter of chain orintheicosahedron. Arepresentativestructural unitcontain ing an Si atom is 〔C B Si〕ε+ 〔B11 C〕ε , whilethe structural unit without Siis 〔C B B ( C)〕δ 〔B11 C〕δ+ . Afteradding Sitotheboroncarbides,theenergyrequired bythe dispro portionation reaction decreases,theconcentrationofthecarriersincreases,andthereare more pathsfor the bipolaron to hopping. At thesametime, the covalent bond becomes weaker, andthethermal conductivity decreases. Therefore, thethermoelectric property of Si dopedboron carbidesisimproved .
关键词:
Si doped boroncarbide
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X.M.Min
,
Y. Daiand C.W.Nan National Key Laboratory of Advanced Technology for Materials Synthesis and Processing
,
Wuhan University ofTechnology
,
Wuhan 430070
,
China
金属学报(英文版)
Al NMRand quantum chemistry calculation have been used to study thestructureof γ Al2O3 and AlON. The NMRspectra arecharacterized bythree distinctresonance peaksat114 , 66 and 12 , corresponding to 〔AlN4〕,〔AlO4〕and 〔AlO6〕respectively. The uantum chemistrycalculationsshowqd thatthe models with vacancieslocated at octahedralsitein B block are morestablethanthose with vacancieslocated attetrahedralsitein A blockforboth of γ Al2 O3 and AlON. In AlON, nitrogen atoms preferentially replace oxygen atoms in〔AlO4〕tetrahedrons, and the model with 〔AlN4〕is morestablethan that with 〔AlO4 xNx〕(x= 1 ,2 and 3) and 〔AlO6 - yNy〕(y= 1 ,2 ,3 and 4) , which isin agreement with theexperimental analysisby NMR.
关键词:
Al2 O3 and AlON
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