Abstract

Crystal structures of four aragonite-group carbonates—aragonite (Ca0.997Sr0.003CO3), calcian strontianite (Ca0.147Sr0.853CO3), cerussite (Ca0.001Pb0.999CO3), and witherite (Sr0.019Ba0.981CO3)—have been refined at ambient conditions, and thermal expansion has been measured over a range of temperatures from 143 to 586 K by single-crystal X-ray diffraction. Average linear thermal expansion coefficients α0(V) are 58(2), 58.3(7), 64(2), and 57(2) (× 10−6 K−1) for aragonite, strontianite, cerussite, and witherite, respectively, throughout the experimental temperature range. Aragonite, strontianite, and witherite have very similar α0(V) values, whereas that of cerussite is significant larger, primarily due to the c-axis thermal expansion for cerussite being much larger than those of the other carbonates. There are no significant differences for α0(a) values among the four carbonates, whereas α0(b) values decrease in the order of aragonite > strontianite > cerussite ≈ witherite, and α0(c) values increase in the order of aragonite < strontianite < witherite < cerussite. Crystal structures were refined for aragonite (184 to 527 K). <Ca-O> vs. T (K) is fitted linearly quite well, with a slope of 5.8(8) × 10−6 (Å/K). Corrected for assumed rigid body motion, the CO3 groups showed no significant change in C-O distances over the temperature range.

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