Abstract
Slawsonite’s (SrAl2Si2O8) structure evolutions depending on temperature (27–1000 °C) have been studied by in situ single-crystal X-ray diffraction. The SrO7 polyhedron expands regularly with the temperature increase. Silicon and aluminum cations are ordered in tetrahedral sites of the studied slawsonite; no significant changes in their distribution as temperature increases were observed. Slawsonite demonstrates a relatively high volume thermal expansion (αV = 23 × 10−6 °C−1) with high anisotropy, typical for framework feldspar-related minerals and synthetic compounds. It was found that, contrary to previously published data, the crystal structure of slawsonite is stable in the studied temperature range and no phase transitions occur up to 1000 °C. The role of Ca and Ba substitution for Sr and Al/Si ordering on polymorphism of natural MAl2Si2O8 (M = Ca, Sr, Ba) is herein discussed.
Highlights
The alkaline earth aluminosilicates with the general formula MAl2Si2O8 (M = Ca, Sr, Ba) are very important both for geology and material sciences
The present study aims to investigate the high-temperature behavior of slawsonite using in situ single-crystal X-ray diffraction data at a temperature range of 27–1000 ◦C in order to clarify whether there are phase transitions and compare the obtained data with the data on other isotypic minerals
The crystal structure of slawsonite is based on a three-dimensional tetrahedral framework that contains four- and eight-membered rings of SiO4 and AlO4 tetrahedra [16], framework channels are occupied by Sr atoms (Figure 2)
Summary
They relate to the feldspars, which are the most common minerals in the Earth’s crust, on the other hand, they are applied as ceramic components [1,2,3], phosphorous (e.g., [4,5,6,7,8,9]), refractories material [10] and matrix for radioactive wastes [11,12,13]. Slawsonite belongs to the feldspar group of minerals. The tetrahedral structures are subdivided into four groups, based on the structural topology, i.e., feldspar, paracelsian, svyatoslavite (all three correspond to three-dimensional frameworks), and dmisteinbergite (layered). According to the classification [14], slawsonite together with paracelsian (BaAl2Si2O8), danburite- (MB2Si2O8, M = Ca, Sr, Ba) and hurlbutite-group minerals (MBe2P2O8, M = Ca, Sr) belong to the minerals with the paracelsian topology
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