Phase transitions and thermal expansion of BaCO3 and SrCO3 up to 1413 K

Abstract

The phase evolution and thermal expansivity of synthetic orthorhombic BaCO 3 (α-BaCO 3 ) and SrCO 3 (α-SrCO 3 ) were studied up to 1413 K using high-temperature powder X-ray diffraction. The α-BaCO 3 phase transformed into a trigonal β phase at 1073–1093 K with an increase in molar volume by 2.7%, and further to a cubic γ phase at 1233–1253 K with 0.2% increase in molar volume. The α-SrCO 3 phase transformed into a trigonal β phase at ∼1173 K. The fitted parameters for volume thermal expansion coefficients (α V ( T ) = a 0 (10 −5 K −1 ) + a 1 (10 −8 K −2 ) T ) are a 0 = 4.0(4), a 1 = 4.0(6) for α-SrCO 3 ; a 0 = 4.4(5), a 1 = 3.9(7) for α-BaCO 3 ; a 0 = 6.5(2) and a 0 = 6.8(1) for the β and γ phase of BaCO 3 , respectively. The β-BaCO 3 phase exhibits negative expansion along the a -axis, which may help to design new materials with tunable thermal behavior when it is mixed with materials with positive thermal expansion. The aragonite-group carbonates (CaCO 3 , SrCO 3 , and BaCO 3 ) have similar bulk thermal expansivity, but their anisotropy and linear expansivities vary with the size of the cation.