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

Abstract

Single crystals of synthetic nickel sulfate monohydrate, α-NiSO 4 ·H 2 O (space-group symmetry C2/c at ambient conditions), were subject to high-pressure behavior investigations in a diamond-anvil cell up to 10.8 GPa. By means of subtle spectral changes in Raman spectra recorded at 298 K on isothermal compression, two discontinuities were identified at 2.47(1) and 6.5(5) GPa. Both transitions turn out to be apparently second order in character, as deduced from the continuous evolution of unit-cell volumes determined from single-crystal X-ray diffraction. The first structural transition from αto β-NiSO 4 ·H 2 O is an obvious ferroelastic C2/c−P1̅ transition. It is purely displacive from a structural point of view, accompanied by symmetry changes in the hydrogen-bonding scheme. The second βto γ-NiSO 4 ·H 2 O transition, further splitting the O2 (hydrogen bridge acceptor) position and violating the P1̅ space-group symmetry, is also evident from the splitting of individual bands in the Raman spectra. It can be attributed to symmetry reduction through local violation of local centrosymmetry. Lattice elasticities were obtained by fitting second-order Birch−Murnaghan equations of state to the p-V data points yielding the following zero-pressure bulk moduli values: K 0 = 63.4 ± 1.0 GPa for α-NiSO 4 ·H 2 O, K 0 = 61.3 ± 1.9 GPa for β-NiSO 4 ·H 2 O, and K 0 = 68.8 ± 2.5 GPa for γ-NiSO 4 ·H 2 O.

Switchable crystal–amorphous states of NiSO4·6H2O induced by a Reddy tube

“…The test crystal exhibits transmittance between 410 and 620 nm wherein the maximum transmittance percentage is observed at 490 nm that is the characteristic of NiSO 4 Á6H 2 O. [41][42][43][44][45] Even under shocked conditions, the test samples have an identical optical transmittance window to that of the control sample ranging from 490 to 620 nm. Hence, it is clear that the water ligands around the nickel ion are not altered by the impact of shock waves.…”

Crystallography relevant to Mars and Galilean icy moons: crystal behavior of kieserite-type monohydrate sulfates at extraterrestrial conditions down to 15 K

“…Compared with the temperature-dependent changes in lattice dimensions discussed above, the high-pressure behavior of the title compounds, investigated recently by Meusburger et al (2019Meusburger et al ( , 2020, Ende et al (2020) and Wildner et al (2021) is characterized by a continuous second-order ferroelastic phase transition from the present monoclinic -phase (C2/c) to a triclinic -phase (space group P1) at pressures of 2.72, 6.15, 2.40 and 2.47 GPa for M 2+ = Mg, Fe, Co and Ni, respectively. Nevertheless, since the cells of the -polymorphs are based on the respective reduced cells of the C2/c -phase, a direct comparison of the lattice dimensions even across the phase transition is still feasible.…”

“…On the one hand, the Fe compound revealing the highest volume thermal expansion V (Table 1) shows, as expected, the highest compressibility and thus the smallest bulk modulus of K 0 ' 45 GPa (Meusburger et al, 2019), albeit close to K 0 of the Mg and Co phases. The Ni compound with the clearly highest bulk modulus K 0 ' 60 GPa (Ende et al, 2020) also exhibits the smallest thermal changes of the axial lengths (h |a,b,c| i ' 2.2 Â 10 À5 K À1 ) but a volume thermal expansion comparable to the Mg and Co phases (Table 1). Among the individual cell axes, the softest c axis upon compression (hM c i ' 125 GPa) most closely follows the expectation of equal slopes in V/V 0 versus l/l 0 plots for pressure and temperature (h c i ' 3.3 Â 10 À5 K À1 ) in Fig.…”

“…Following our investigations on the structural crystallography of kieserite-type solid solutions: M 2+ SO 4 ÁH 2 O (M 2+ = Mg, Fe, Co, Ni), including the temperature-dependent behavior of the end members at temperatures prevailing at equatorial martian latitudes (Bechtold & Wildner, 2016;Talla et al, 2020), we recently carried out investigations under high-pressure conditions relevant to the interior of individual icy moons (Meusburger et al, 2019(Meusburger et al, , 2020Ende et al, 2020;Wildner et al, 2021). These experimental studies revealed a second-order phase transition from the monoclinic -phase (space group C2/c) to a triclinic -phase (space group P1) at critical transition pressures ranging from 2.40 (Co) to 6.15 GPa (Fe).…”

X-ray diffraction reveals two structural transitions in szomolnokite

“…DOI: https://doi.org/10.2138/am-2022-8147. http://www.minsocam.org/ Revision 1 Pardo et al, 2022 American Mineralogist to occur in the Mg-endmember kieserite (MgSO 4 H 2 O) at lower pressures (Meusburger et al 2020), the Ni-endmember dworknikite (NiSO 4 H 2 O) (Ende et al 2020), and the Co-endmember (CoSO 4 H 2 O) (Wildner et al 2021).…”