YMnO3 & YMn2/3Tm1/3O3電子及原子結構之研究 (Tm= Co, Ni and Cu)

Electronic and atomic structures of YMnO3 and YMn2/3Tm1/3O3 (Tm= Co, Ni and Cu)

陳昱昕(Yu-Shin Chen)

指導教授 ： 彭維鋒

淡江大學/理學院/物理學系碩士班/碩士(2009年)

https://doi.org/10.6846/TKU.2009.00408

摘要

利用X光吸收光譜 (X-ray Absorption Spectroscopy, XAS)，研究其以3d過渡金屬摻雜其釔錳氧化物 (YMnO3)-YMn2/3Tm1/3O3 (Tm= Co, Ni and Cu)之電子及原子結構。Mn L3-edge及K-edge結果顯示Tm2+取代了部分Mn3+，而使得Mn離子電荷價數增加。Tm2+的摻雜使得Mn 3d未佔據態變寬而不侷限其局部區域性，進而增進其導電性。由局域密度近似 (Local Spin Density Approximation + Hubbard U parameter，LDA+U)計算電子態密度與X光吸收譜圖比較得知，YMn2/3Ni1/3O3中，造成Mn L3-edge未佔據態改變的是Mn 3d↑-spin eg而不是一般認為的Mn 3d t2g。且O K-edge第二吸收峰為O 2p與Ni 3d↓-spin eg之混成 (hybridized)。

關鍵字

XANES ； EXAFS ； 錳氧化物 ； LDA+U

並列摘要

X-ray absorption spectroscopy measurements have been performed to elucidate local electronic and atomic structures of 3d-transition metal doped yttrium manganites (YMnO3) with chemical formula YMn2/3Tm1/3O3 (Tm= Co, Ni and Cu). The Mn L3-edge and K-edge XANES results indicate the direct substitution of Tm2+ for Mn3+, so that the positive effective charge of Mn ions are increased. Tm-doping is also found to induce substantial broadening of the Mn L3-edge feature, which suggests enhancement of the delocalization of Mn 3d eg subbands and conductivity. Local spin density approximation (LDA) + U (Hubbard U parameter) calculation shows that the leading features in the Mn L3-edge XANES spectra of YMn2/3Tm1/3O3 are due to majority-spin Mn eg subband rather than the Mn t2g subband commonly assigned. The comparison between O K-edge XANES spectrum of YMn2/3Ni1/3O3 and the LDA+U calculation shows significant contribution of O 2p and minority-spin Ni 3d eg hybridized states to the second feature of the O K-edge XANES spectra.

並列關鍵字

XANES ； EXAFS ； manganites ； LDA+U

參考文獻

1.H. Y. Hwang, S. W. Cheong, P. G. Radaelli, M. Marezio, and B. Batlogg, Phys. Rev. Lett. 75, 914 (1995).

2.C. Zener, Phys. Rev. 82, 403 (1951).

3.J. H. Park, S. W. Cheong, and C. T. Chen, Phys. Rev. B 55, 11072 (1996).

4."X-Ray Absorption : Principles, Application, Techniques of EXAFS, SEXAFS, SEXAFS and XANES", edited by D. C. Koningsberger and R. Prins, Chem. Analysis 92 (Wiley, New York, 1988).

5.D. E. Sayers, E. A. Stern, and F. W. Lytle, Phys. Rev. Lett. 27, 1024 (1971).