Strain-Induced Segmentation of Magnesian Calcite Thin Films Growing on a Calcite Substrate

Abstract

In crystal growth of mineral species or different compositional members of a solid solution on one another, the degree of lattice mismatch at their interface affects the growth pattern of the precipitating mineral phase. Fast layer-by-layer growth of magnesian calcite on pure calcite (1014) substrates has been observed at Mg 2+ /Ca 2+ ratios of 2-7 using in situ atomic force microscopy. Under solution conditions of calcite saturation states starting from Ω ≈ 33, depending on Mg 2+ /Ca 2+ ratios and carbonate content, bulging in the epitaxial magnesian calcite thin film led to the formation of networks of ridges along the [441], [481], and [421] directions. Eventually, spreading of monolayers stopped at the ridges and formed stationary multilayer steps, resulting in separate and individually growing crystal segments. Molecular dynamics computational modeling suggests that relaxation of strain energy, caused by the interfacial lattice mismatch between pure calcite and the isostructural magnesium-containing phase with smaller lattice constants, leads to a semicoherent interface and disordered linear zones cutting through the thin film. As a consequence, the surface bulges up in a way similar to our laboratory observations. This strain-induced segmentation produces aggregates of aligned microcrystals and increase knowledge of the behavior of strained thin films in general.