The modulated structure of synthetic Co-åkermanite, Ca₂CoSi₂O₇

Abstract

Diffraction patterns of synthetic Co-akermanite, Ca 2 CoSi 2 O 7 , reveal distinct satellite reflections at room temperature. An incommensurate modulation in this material has been determined by five-dimensional refinement pf the structure. The basic structure is tetragonal P42 1 m, unit-cell dimensions a=7.8417 (6), c=5.0249 (3) A, V=308.99 A 3 , Z=2, M r =307.26, D m =3.307 (4) g cm -3 at 293 K, D x =3.302 g cm -3 , Mo Kα with graphite monochromator, μ=47.7 cm -1 , F(000)=302, R=0.049 for 734 unique reflections