Naoyuki Nogi1, Satoru Tanaka1 and Tetsuji Noda2
1Department of Quantum Engineering and Systems Science, The University of Tokyo, Tokyo 113-8656
We have measured infrared-reflectance spectra at room temperature of isotopically (10B or 11B) enriched, blended (42 at%10B and 58 at%11B) and natural (19.8 at%10B and 80.2 at%11B) β-rhombohedral boron. For the A2u and Eu modes of 10B, 11B and natural boron which were observed with light polarization parallel or perpendicular to the c-axis, the mode frequency ω of each symmetry changed with the classical harmonic approximation.
The mode frequency of inter- or several intra- icosahedral modes of an isotopically mixed crystal was lower than expected frequency from the harmonic model. It is possible that isotopic disorder-induced frequency shifts, which is an anharmonic effect, is obtained by using isotope-modified samples.
(Received April 26, 1999; In Final Form August 24, 1999)
phonons, isotope effect, β-rhombohedral boron, infrared reflectance spectra, A2u-mode, Eu-mode, isotopic disorder, anisotropy
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