Polymorphism of Mg-monohydrate sulfate kieserite under pressure and its occurrence on giant icy jovian satellites

High-Pressure Behavior of Nickel Sulfate Monohydrate: Isothermal Compressibility, Structural Polymorphism, and Transition Pathway

“…The values for the β-NiSO 4 ·H 2 O polymorph in the range 2.5 to 6.0 GPa correspond to K 0 = 44.5 ± 9.4 GPa and K′ = 8.2 ± 3.2, with a relatively high value for K′ due to obvious elastic softening effects as reported for the isostructural phases. 27,28 When the p range is restricted between 4.0 and 6.0 GPa, the fit yields a 500% error value for K 0 and K′ for BM- 3 Table 1) and might be indicative for the structural instability of the phase at even higher pressures beyond the maximum p within this experimental series. High-Pressure Crystal Structures.…”

“…The careful analysis of the spectra ( Figure 2) shows that the second band component starts emerging at p ≥ 7.41(6) GPa, and thus these spectral changes coincide with the second supposed discontinuity as described above. Considering that for the earlier reported C2/c-P1̅ transition in isostructural compounds 27,28 the structures of both polymorphs exhibit just one single S position, the second structural change must be accompanied by continued symmetry breaking, leading to the diversification of more than one S site. The current observation may thus be a possible indication of another structural change, which has not yet been recognized so far.…”

“…Indexing of the reconstructed reciprocal space yielded monoclinic lattice metrics for the measurements at 0.6(1) and 2.3(1) GPa, while at 4.5(1) and 8.4(1) GPa triclinic metrics were found. Initial positional parameters for the refinements were assigned according to those reported by Meusburger et al 28 All refinements were carried out using scattering curves from the International Tables for Crystallography 40 and isotropic displacement parameters for all atoms using SHELXL 41 (Figure 1) and 970−1190 cm −1 (Figure 2) revealed the most prominent bands as described for isostructural MgSO 44 The high-p spectra reveal the typical average blueshifts with Δν ̅ /Δp values ranging between 2.42(7) and 7.45(8) cm −1 GPa −1 (Figure 3). The spectral evolution and the lack of drastic changes with respect to band positions, numbers, and intensities of modes suggest that the structural topology should be largely retained across the recorded p range.…”

“…Comodi et al 51 and McCord et al 52 ). α-MgSO 4 ·H 2 O and β-MgSO 4 ·H 2 O have recently been considered for the interior of Callisto, 28 where the maximum pressure corresponds to around 5 GPa. Considering the significant Ni contents in the soluble sulfate fraction in C1/C2 carbonaceous chondrites believed to be chemically similar to the rocky cores of the icy moons (e.g., Ivuna and Orgueil) and meteorites with up to 13.6 wt % NiO, 13 NiSO 4 ·H 2 O can be considered as an important component in natural monohydrate sulfates.…”

“…16,25 Recent investigations on MgSO 4 ·H 2 O and FeSO 4 ·H 2 O under hydrostatic compression revealed a ferroelastic phase transition following the translationsgleiche C2/c-P1̅ group−subgroup relation and being apparently second order in its thermodynamic character. 27,28 Any of the symmetry changes follow a pattern of atom displacements related to the changes within the hydrogen bonding systems, whereas the topology of the heterodesmic frameworks remains unchanged, apart from distortion originating from symmetry breaking. In this context, synthetic NiSO 4 ·H 2 O single crystals are investigated in this study with respect to the occurrence of an equivalent structural polymorphism.…”