新型BCN化合物的结构表征和相转变

Structural characterization and phase transition of an unknown phase of boron carbon nitride compound

将石墨和六方氮化硼(h_BN)混合粉球磨120h形成的非晶B-C-N粉在4.5GPa,1600K等温退火45min.XRD,TEM和Raman散射测量结果表明,高压合成的产物由晶格常数为a1=0.2551nm,c1=0.6716nm的六方Ⅰ相和a2=1.2360nm,c2=0.8570nm的六方Ⅱ相组成,其中六方Ⅱ相为B-C-N新相.在室温该新相在1279,1368,1398cm-1出现三个特征Raman峰.变温Raman测量结果表明,在测量温度T=93K时,样品中的主要相为六方Ⅰ相,随着温度的升高,六方Ⅰ相逐渐向六方Ⅱ相转变,当T>473K时,六方Ⅰ相完全转变成六方Ⅱ相.当温度从673K降到93K过程中,样品又从六方Ⅱ相逐渐变回到六方Ⅰ相.对这一相变的机理进行了讨论.

Amorphous BCN was prepared by ball milling the mixture of graphite and hexagonal BN for 120h, and then annealed for 45 min. at 1600K under 4.5GPa. The XRD, TEM and Raman scattering measurement indicated that the as-prepared sample consists of hexagonal phase Ⅰ- with lattice constants α1 = 0.2551nm and c1 = 0.6716nm and hexagonal phase Ⅱ with lattice constants α2 = 1.2360nm and c2 = 0.8570nm, of which the hexagonal phase Ⅱ is an unknown phase of boron carbon nitride. Three characteristic Raman peaks located at 1279, 1368 and 1398cm^-1 respectively, were observed in the Raman spectra recorded at room temperature. The temperature dependent Raman scattering spectra of the sample were taken at temperature ranging from 93 to 673K. The measuring results indicate that the hexagonal phase of Ⅰmainly exist in the sample at 93K and hexagonal phase of convert to hexagonal phase of Ⅱcompletely when at above 473K. The phase transition from the hexagonal phase of Ⅰto Ⅱ occurs with increasing temperature, vice versa. The mechanism of the phase transition is discussed in the present work.