Setsuo Takeno
Hiroshima University
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Physics and Chemistry of Minerals | 1996
Takuo Tamura; Akira Yoshiasa; Kazuaki Iishi; Setsuo Takeno; Hironobu Maeda; Shuichi Emura; Kichiro Koto
The local structure around Co, Zn and Sr atoms in incommensurately modulated, melilite-type X2T1 T22O7 (X=Ca and Sr, T1=Mg, Co and Zn, T2=Si) solid-solutions has been investigated by EXAFS analyses. The modulated structure was confirmed in Ca2-xSrxCoSi2O7 solid-solutions with X=0.0 to 0.6 and for both Ca2Mg1-YCoYSi2O7 and Ca2Mg1-YZnYSi2O7 solid-solutions over the whole compositional range at room temperature.The actual bond-distances determined by the EXAFS method for the T1 site (Co-, Zn-O) in the modulated structure are longer than the mean bond-distances obtained from the X-ray diffraction method. This is attributable to the libration of the T1 tetrahedra. In the Ca1-XSrXCoSi2O7 solid-solution both the Sr-O and Co-O distances by the EXAFS method for the X-site increase from Ca end-member to Sr end-member. These increases are respectively 0.8% and 0.6%. This means the local expansions of the tetrahedral sheets and of the XO polyhedra are well matched. In the modulated Ca2Co1-YMgYSi2O7 and Ca2Zn1-YMgYSi2O7 solid-solutions, the actual Co-O and Zn-O distances for the T1-sites are nearly constant in the whole compositional range. The compositional variations of the local structure around the cations in the solid-solution are different for the X and T1 sites.It is concluded that the local geometric restriction for the size of substituted cation in X site is larger than that in T1 site. The dimension of the tetrahedral sheet puts restriction on the size of the cations situated at the interlayer X sites. In other words, the different behavior of the local geometric restriction between the X and T1 sites is an important feature of the melilite structure and is also related to the modulated structure.
Meteoritics & Planetary Science | 2000
Yuji Sano; Kentaro Terada; Setsuo Takeno; L. A. Taylor; Harry Y. McSween
American Mineralogist | 1992
Makio Ohkawa; Akira Yoshiasa; Setsuo Takeno
Clay science | 1996
Armand Wouatong; Ryuji Kitagawa; Setsuo Takeno; Félix M. Tchoua; Daniel Njopwouo
Mineralogical Journal | 1994
Makio Ohkawa; Akira Yoshiasa; Setsuo Takeno
Mining geology | 1988
Ryuji Kitagawa; Hirotsugu Nishido; Zuisho Ito; Setsuo Takeno
Mining geology | 1988
Ryuji Kitagawa; Hirotsugu Nishido; Setsuo Takeno
Mineralogical Journal | 1983
Ryuji Kitagawa; Setsuo Takeno; Ichiro Sunagawa
The Journal of the Japanese Association of Mineralogists,Petrologists and Economic Geologists | 1979
Akira Soeda; Setsuo Takeno; Makoto Watanabe
Zeitschrift Fur Kristallographie | 1997
Makio Ohkawa; S. Fujita; Setsuo Takeno; A. Nakatsuka; Akira Yoshiasa; M. Uchida; Kazumasa Ohsumi