| Summary: | 碩士 === 國立臺灣師範大學 === 物理學系 === 100 === We present the Raman-scattering studies of Zn doped LiCu2O2 single crystals and Ho doped MnS polycrystalline samples. Our aim is to investigate the effects of doping on the lattice excitations in these novel materials.
First, room-temperature Raman-scattering spectrum of LiCu2O2 shows ten phonon modes at about 106 cm-1, 119 cm-1, 173 cm-1, 297 cm-1, 362 cm-1, 465 cm-1, and 557 cm-1 as well as 161 cm-1, 494 cm-1 , and 569 cm-1, displaying symmetries of Ag and B1g, respectively. As the concentration of the Zn ion increases (x = 0.03 and 0.07), there are three important features to these spectra: (i) the 161 cm-1 phonon mode that is associated with the oxygen vibrations along the ab-plane exhibits a redshift, consistent with the lattice dilatation observed in the x-ray diffraction data; (ii) the 106 cm-1 peak belongs to the lattice origin, rather than the two-magnon continuum assigned by Phys. Rev. B 69, 104421 (2004).; (iii) the 492 cm-1 phonon mode of 7 % Zn doped sample shows a slight redshift below the magnetic phase transition of 14 K, indicating a spin-phonon coupling.
Second, room-temperature Raman-scattering spectrum of Ho0.01Mn0.99S shows four phonon modes at about 135 cm-1, 227 cm-1, 333 cm-1 and 585 cm-1. With increasing Ho content, there are also three important features to these spectra: (i) the 333 cm-1 and 585 cm-1 phonon modes exhibit a redshift due the larger ionic size of Ho; (ii) diffusive-type Raman-scattering response appears at low temperatures, which is likely related with the carrier collision-dominated mechanism; (iii) the spectral weight of the 333 cm-1 and 585 cm-1 phonon modes decreases at about 350 K, 500 K, and 620 K. These results correlate with the variations of electric resistivity and the lattice constant, suggesting the possibility of orbital-ordering, or charge-ordering phenomena.
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