Abstract
High-temperature Ba2[Si4O10] is monoclinic with a = 23.202(5) Å, b = 4.661(1) Å, c = 13.613(4) Å, β = 97.54(2)°, C2/c, Z = 6. Using 635 independent intensities of h0l, h1l and h2l reflections its structure was determined and refined to a residual R of 7.3%. High-temperature Ba2[Si4O10] contains [Si4O10] Zweierschichten similar to those in sanbornite, low-temperature Ba2[Si4O10], but with different topology. The two crystallographically non-equivalent barium ions in high-temperature Ba2[Si4O10] have 8 + 2 and 9+1 near oxygen neighbours. The slightly lower degree of convolution of the [Si4O10] layers in comparison with those of sanbornite is explained by the increased ionic size of barium due to larger thermal motions.

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