Spectroscopic ellipsometry investigations of the thermally induced first-order transition of Rbmn[Fe(CN)6]
Spectroscopic ellipsometry investigations of the thermally induced first-order transition of Rbmn[Fe(CN)6]
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Rbmn[Fe(CN)6]热致一级跃迁的光谱椭圆光度研究
DOI：
10.1103/physrevb.78.014303
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发表时间：
2008
影响因子：
3.7
通讯作者：
K. Boukheddaden
中科院分区：
文献类型：
--
作者：
E. D. Loutete;E. Codjovi;H. Tokoro;P. Dahoo;S. Ohkoshi;K. Boukheddaden
We report on detailed spectroscopic ellipsometry investigations on the thermally induced first-order phase transition of rubidium manganese hexacyano-ferrate $(\text{RbMn}[\text{Fe}{(\text{CN})}_{6}])$ pellet sample. This switchable solid shows a cooperative Jahn-Teller distortion coupled with a local charge transfer between Fe and Mn ions. Optical spectra of the real, ${\ensuremath{\epsilon}}^{\ensuremath{'}}$, and imaginary, ${\ensuremath{\epsilon}}^{\ensuremath{''}}$, parts of the complex dielectric constant have been recorded in the interval of temperature, i.e., 250\char21{}350 K, around the transition region and in the optical range of 190\char21{}830 nm. Four (two) optical bands have been identified and assigned in the low-temperature (high-temperature) phase, corresponding to the ${\text{Fe}}^{\text{II}}{\text{-CN-Mn}}^{\text{III}}$ $({\text{Fe}}^{\text{III}}{\text{-CN-Mn}}^{\text{II}})$ state. We performed a quantitative analysis by fitting our spectra with Gauss-Lorentz (GL) line shapes and determined the energy positions, oscillator strengths, and widths of individual transitions, as well as their thermal variation. It has been found that the GL profiles excellently approximate the optical response. Moreover, we observed a significant shift of the metal-ligand charge-transfer band8 upon the thermal transition and correlated it quantitatively to the volume change at the transition. We then derived the coefficient of the volumetric thermal expansion of the title compound and found $\ensuremath{\alpha}=(\ensuremath{\partial}V/\ensuremath{\partial}T)/\overline{V}\ensuremath{\simeq}3.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }{\text{K}}^{\ensuremath{-}1}$ in the transition region and ${\ensuremath{\alpha}}_{T}^{LT}\ensuremath{\simeq}4.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }{\text{K}}^{\ensuremath{-}1}$ $({\ensuremath{\alpha}}_{T}^{HT}=8.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }{\text{K}}^{\ensuremath{-}1})$ in the low-temperature (high-temperature) region, in very good agreement with the reported zero thermal-expansion character of this compound. Finally, from the analysis of the integrated absorption spectra, we derived the thermal hysteresis of the high-temperature fraction, which was found in very good agreement with that of magnetic data recorded on the same sample.
We report on detailed spectroscopic ellipsometry investigations on the thermally induced first-order phase transition of rubidium manganese hexacyano-ferrate $(\text{RbMn}[\text{Fe}{(\text{CN})}_{6}])$ pellet sample. This switchable solid shows a cooperative Jahn-Teller distortion coupled with a local charge transfer between Fe and Mn ions. Optical spectra of the real, ${\ensuremath{\epsilon}}^{\ensuremath{'}}$, and imaginary, ${\ensuremath{\epsilon}}^{\ensuremath{''}}$, parts of the complex dielectric constant have been recorded in the interval of temperature, i.e., 250\char21{}350 K, around the transition region and in the optical range of 190\char21{}830 nm. Four (two) optical bands have been identified and assigned in the low-temperature (high-temperature) phase, corresponding to the ${\text{Fe}}^{\text{II}}{\text{-CN-Mn}}^{\text{III}}$ $({\text{Fe}}^{\text{III}}{\text{-CN-Mn}}^{\text{II}})$ state. We performed a quantitative analysis by fitting our spectra with Gauss-Lorentz (GL) line shapes and determined the energy positions, oscillator strengths, and widths of individual transitions, as well as their thermal variation. It has been found that the GL profiles excellently approximate the optical response. Moreover, we observed a significant shift of the metal-ligand charge-transfer band8 upon the thermal transition and correlated it quantitatively to the volume change at the transition. We then derived the coefficient of the volumetric thermal expansion of the title compound and found $\ensuremath{\alpha}=(\ensuremath{\partial}V/\ensuremath{\partial}T)/\overline{V}\ensuremath{\simeq}3.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }{\text{K}}^{\ensuremath{-}1}$ in the transition region and ${\ensuremath{\alpha}}_{T}^{LT}\ensuremath{\simeq}4.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }{\text{K}}^{\ensuremath{-}1}$ $({\ensuremath{\alpha}}_{T}^{HT}=8.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }{\text{K}}^{\ensuremath{-}1})$ in the low-temperature (high-temperature) region, in very good agreement with the reported zero thermal-expansion character of this compound. Finally, from the analysis of the integrated absorption spectra, we derived the thermal hysteresis of the high-temperature fraction, which was found in very good agreement with that of magnetic data recorded on the same sample.