Crystal structure and thermal expansion of aragonite-group carbonates by single-crystal X-ray diffraction

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 relined 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 alpha(0)(V) are 58(2), 58.3(7), 64(2), and 57(2) (x 10(-6) K-1) for aragonite, strontianite, cerussite, and witherite, respectively, throughout the experimental temperature range. Aragonite, strontianite, and witherite have very similar alpha(0)(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 alpha(0)(a) values among the four carbonates, whereas alpha(0)(b) values decrease in the order of aragonite > strontianite > cerussite witherite, and alpha(0)(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) x 10(-6) (angstrom/K). Corrected for assumed rigid body motion, the CO3 groups showed no significant change in C-O distances over the temperature range.