Specific five-fold coordinated sites observed in the oxides and silicates with derivative structure

Abstract

Five-fold coordination of cation site is pointed out to be rarely observed in ionic crystals in comparison with the frequent appearance of four and six fold coordination. The specific five fold coordinated sites of Fe(3+) ion occurring at the boundary region between the fundamental structure units were discussed. The structural studies on Sr4Fe6O13 consisting of alternate slabs of the perovskite type Sr2Fe2O5 and of Fe2O3 parallel to (010) have been carried out. The coordinations of Sr, Fe and O atoms in the respective slabs were examined. Based on the ionic radii of Shannon, the distances of Fe(3+)-O and Fe-O were estimated. Bond valences calculated from the equation of Brown and Altermatt were shown in a table. Inconsistencies of the values due to the long Fe-O distances were recognized for the oxygen ions coordinated to the Fe(3+) ions. A relationship between the mean Fe-O distances and the degree of distortion for five-coordinated sites was shown in a figure. It was found that five coordinated Fe sites frequently have long mean Fe-O distances similar to that of six-coordinated Fe sites.

イオン結晶における陽イオンサイトの5回対称配位は、4回対称および6回対称配位の出現頻度に比較すると、まれにしか観察されないことを指摘した。構造基本単位の間の境界領域に発生するFe(3+)イオン固有の5回対称配位サイトを論じた。(010)に平行なペロブスカイト型Sr2Fe2O5スラブとFe2O3スラブが交互に構成するSr4Fe6O13の構造を研究した。それぞれのスラブ内のSr、Fe、および酸素原子の配位を調べた。シャノンのイオン半径に基づき、Fe(3+)-OおよびFe-Oの距離を推定した。Brown-Altermattの方程式から結合原子価を計算し表に示した。Fe(3+)イオンに対して配位した酸素イオンについては、長いFe-O距離が原因の値の不一致を認めた。Fe-O平均距離と5-配位サイトに対する歪みの度合いとの間の関係を図に示した。5-配位Feサイトは6-配位Feサイトと同様にしばしば長いFe-O平均距離をもつことが分かった。