R2: Crystal structure, crystal chemistry, physical properties of minerals, crystal growth and applied mineralogy

[R2-02] Chemical formula, crystal structure and dielectric properties of swedenborgite

*Hidetomo Hongu¹, Akira Yoshiasa¹, Mayu Yoshihara¹, Ginga Kitahara¹, Kohei Unoki¹, Makoto Tokuda², Kazumasa Sugiyama², Koichi Momma³, Ritsuro Miyawaki³ (1. Kumamoto Univ., 2. Tohoku Univ., 3. National Museum of Nature and Science)

Keywords:swedenborgite, bromellite, chemical formula, structure refinement, dielectric properties

In this study, we determined the chemical formula of swedenborgite using SEM/EDS and Sb XAFS analysis. The chemical formula of swedenborgite can be expressed as (Na_1-xCa_x)Be_4-0.5xSbO₇ (x ≦ 0.05). The crystal structure of swedenborgite [space group P6₃mc, a = 5.4402(10), c = 8.8690(9) Å, Z = 2] was analyzed using single-crystal X-ray diffraction method and was refined to the R1 value of 0.012 for 1573 unique reflections. Considering the arrangement of atoms in the structure, swedenborgite has strong dielectric properties.