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Raman spectra of the products
It is well-known that Raman spectra are an important tool for identifying the lattice dynamics and the crystal electric field splitting of rare-earth hexaborides¡£ Fig 8 shows Raman spectra of RB6 nanocubes and nanoparticles,respectively¡£According to group theory, the hexaboridess tructure has a Pm3m cubic symmetry,which contains A1g+Eg+T1g+T2g+2T1u+T2u vibrational modes, where A1g, Eg, and T2g are Raman activephonons¡£The A1g and Eg modes originate from the stretching vibration of B¨CB bonds and T2g is due to the valence angle bending of B¨CB¨CB in the boron lattice¡£ It can be seen that the sespectra are shifted along the vertical direction,and the order corresponds to the decrease of the lattice constants of RB6 from the top to bottom¡£    However,the peaks of Raman spectra of the same compound of RB6 nanocubes and nanoparticles remain unchanged  in  the  present experiment¡£The three expected main peaksare observed around680cm_1 (T2g), 1140cm_1 (Eg) and1260cm_1 (A1g), which are inagreement with earlier reports [32¨C34], and they completelysatisfy the polarization selection rule in the cubic symmetry¡£ These three prominent peaks are additional  confirmation for the formation of hexaborides because the peaks obey these lection rule for the hexaborides¡¯cubic symmetry¡£ Abroad peak around 1400cm-1, labeled as *, is commonly observed with a relatively strong intensity for trivalent and intermediate-valent crystals¡£ For trivalentcase,twice the energy of T2g is slightly lower than the peak energy,however,the peak energy systematically follows twice the energy of  T2g¡£ In LaB6, the peak energy is far from twice the energy of T2u and that of T2g is very close to the peak energy¡£For SmB6 the energy coincidence is very good¡£Thus it can be concluded that the peak observed in the trivalent case originates from these cond-order process of  T2g¡£

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Raman spectra of the products ÑùÆ·µÄÀ­Âü¹âÆ×Ñо¿
It is well-known that Raman spectra are an important tool for identifying the lattice dynamics and the crystal electric field splitting of rare-earth hexaborides¡£
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Fig 8 shows Raman spectra of RB6 nanocubes and nanoparticles,respectively¡£
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According to group theory, the hexaboridess tructure has a Pm3m cubic symmetry,which contains A1g+Eg+T1g+T2g+2T1u+T2u vibrational modes, where A1g, Eg, and T2g are Raman activephonons¡£
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The A1g and Eg modes originate from the stretching vibration of B¨CB bonds and T2g is due to the valence angle bending of B¨CB¨CB in the boron lattice¡£
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It can be seen that the sespectra are shifted along the vertical direction,and the order corresponds to the decrease of the lattice constants of RB6 from the top to bottom¡£   
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However,the peaks of Raman spectra of the same compound of RB6 nanocubes and nanoparticles remain unchanged  in  the  present experiment¡£
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The three expected main peaksare observed around680cm_1 (T2g), 1140cm_1 (Eg) and1260cm_1 (A1g), which are inagreement with earlier reports [32¨C34],
ÕýÈçËùÆÚ´ýµÄÄÇÑù£¬Èý¸öÖ÷ÒªµÄÀ­Âü·å³öÏÖÔÚ 680 m_1 (T2g), 1140cm_1 (Eg) and1260cm__1 (A1g)£¬ÕâºÍÔçÏȵÄÎÄÏ×±¨µÀÒ»Ö¡£
and they completelysatisfy the polarization selection rule in the cubic symmetry¡£
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These three prominent peaks are additional  confirmation for the formation of hexaborides because the peaks obey these lection rule for the hexaborides¡¯cubic symmetry¡£
ÕâÈý¸öÍ»³öµÄ·å£¬¸ü¼Ó֤ʵÁËÁù½ÇÅð»¯Îï½á¹¹µÄÐγɣ¬ÒòΪÕâЩ·å×ñ´ÓÕâЩÁù½ÇÁ¢·½¶Ô³ÆÐÔµÄÑ¡Ôñ¶¨Ôò
Abroad peak around 1400cm-1, labeled as *, is commonly observed with a relatively strong intensity for trivalent and intermediate-valent crystals¡£
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For trivalentcase,twice the energy of T2g is slightly lower than the peak energy,however,the peak energy systematically follows twice the energy of  T2g¡£
¶ÔÓÚ3¼ÛÇé¿ö£¬T2gµÄË«±¶ÄÜÁ¿±ÈÆð¸Ã·åµÄÄÜÁ¿ÉÔС£¬Õâ¸ö·åÄÜÁ¿ÏµÍ³µØ½ôËæT2gÄÜÁ¿µÄÁ½±¶Öµ¡£
In LaB6, the peak energy is far from twice the energy of T2u and that of T2g is very close to the peak energy¡£
ÔÚLaB6ÖУ¬·åÄÜÁ¿±ÈÆðT2uµÄ2±¶ÄÜÁ¿ÒªÐ¡ºÜ¶à¡£µ«ÊÇT2gµÄ2±¶ÄÜÁ¿È¥ºÜ½Ó½ü·åÄÜÁ¿¡£
For SmB6 the energy coincidence is very good¡£Thus it can be concluded that the peak observed in the trivalent case originates from these cond-order process of  T2g¡£
¶ÔÓÚSmB6£¬ÄÜÁ¿µÄ·ûºÏÒ²·Ç³£ºÃ¡£Òò´Ë£¬¿ÉÒԵóö½áÂÛ£¬ÔÚ3¼ÛÇé¿öϹ۲쵽µÄ·åÀ´Ô´ÓÚT2gµÄcond-order¹ý³Ì¡£
2Â¥2009-12-18 10:54:19
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