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Structural determination of atomic substitution ratio in (K_<1-x>Rb_x)_2SeO_4 mixed crystal system

Journal of the Physical Society of Japan Volume 74 Issue 10 Page 2748-2753
published_at 2005
2008010259.pdf
[fulltext] 249 KB
Title
Structural determination of atomic substitution ratio in (K_<1-x>Rb_x)_2SeO_4 mixed crystal system
Creators Sawae Shinsuke
Creators Nakashima Terumi
Creators Shigematsu Hirotake
Creators Kasano Hironobu
Creators Mashiyama Hiroyuki
Creator Keywords
potassium selenate rubidium selenate mixed crystal substitution ratio structure analysis phase transition sublattice model soft phonon dispersion
In order to explain why Rb_2SeO_4 remains in normal phase down to 0 K while K_2SeO_4 transforms into the modulated phase at finite temperature, crystal structures of the mixed system have been refined at room temperature by X-ray single crystal analysis. Rb ion can be substituted for K ion with keeping the macroscopic symmetry of space group Pnam. Larger size of Rb ion occupies preferentially site 1, while smaller K ion prefers site 2. Here the atomic distance between an alkali ion and oxygen atoms is longer at site 1 than at site 2. The mean substitution ratio coincides with that from chemical analysis, however, the crystallographic structure analysis is only one method to determine the ratios at each site separately. A sublattice model is discussed to interpret the ion replacing effect on the phonon dispersion relation of the mixed crystal system. The hardening of the soft mode branch can be predicted by the change of interactions between the SeO_4 tetrahedrons if the alkali ions are replaced.
Languages eng
Resource Type journal article
Publishers The Physical Society of Japan
Date Issued 2005
Rights
Copyright c (2002)The Physical Society of Japan()
File Version Author’s Original
Access Rights open access
Relations
[ISSN]0031-9015
[NCID]AA00704814
https://doi.org/10.1143/JPSJ.74.2748
[isVersionOf] [URI]http://www.ipap.jp/jpsj/index.html
Schools 大学院理工学研究科(理学)