High-Pressure Behavior of Nickel Sulfate Monohydrate: Isothermal Compressibility, Structural Polymorphism, and Transition Pathway.
Inorg Chem 2020;
59:6255-6266. [PMID:
32293173 PMCID:
PMC7201398 DOI:
10.1021/acs.inorgchem.0c00370]
[Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Single crystals of
synthetic nickel sulfate monohydrate, α-NiSO4·H2O (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 α- to β-NiSO4·H2O 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 β- to γ-NiSO4·H2O 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: K0 = 63.4 ± 1.0 GPa for α-NiSO4·H2O, K0 = 61.3 ± 1.9 GPa for
β-NiSO4·H2O, and K0 = 68.8 ± 2.5 GPa for γ-NiSO4·H2O.
Synthetic nickel sulfate monohydrate
crystals (space group C2/c at ambient
conditions) were subject to in situ high-pressure solid-state investigations
(structure from single crystal X-ray diffraction, lattice parameter,
Raman spectra) in a diamond-anvil cell up to 10.8 GPa. Two discontinuities,
apparently phase transitions of second order, were identified at 2.47
± 0.01 (obvious ferroelastic C2/c−P1̅) and 6.5 ± 0.5 GPa (P1̅−P1̅). Birch−Murnaghan
equations of state were fitted to the P−V data, and the obtained parameters are given.
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