Ende Martin, Kirkkala Terhi, Loitzenbauer Michael, Talla Dominik, Wildner Manfred, Miletich Ronald
Department of Mineralogy and Crystallography, University of Vienna, Althanstraße 14, A-1090 Wien, Austria.
Department of Chemistry, University of Jyväskylä, Survontie 9 B, Ylistönrinne, FI-40014 Jyväskylä, Finland.
Inorg Chem. 2020 May 4;59(9):6255-6266. doi: 10.1021/acs.inorgchem.0c00370. Epub 2020 Apr 15.
Single crystals of synthetic nickel sulfate monohydrate, α-NiSO·HO (space-group symmetry 2/ 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-NiSO·HO is an obvious ferroelastic 2/-1̅ 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-NiSO·HO transition, further splitting the O2 (hydrogen bridge acceptor) position and violating the 1̅ 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 - data points yielding the following zero-pressure bulk moduli values: = 63.4 ± 1.0 GPa for α-NiSO·HO, = 61.3 ± 1.9 GPa for β-NiSO·HO, and = 68.8 ± 2.5 GPa for γ-NiSO·HO.
对合成的一水合硫酸镍单晶α-NiSO₄·H₂O（在环境条件下空间群对称性为P2₁/c）在金刚石对顶砧池中进行了高达10.8 GPa的高压行为研究。通过在298 K等温压缩时记录的拉曼光谱中的细微光谱变化，在2.47(1) GPa和6.5(5) GPa处识别出两个不连续点。从单晶X射线衍射确定的晶胞体积的连续演化推断，这两个转变显然都是二级特征。从α-NiSO₄·H₂O到β-NiSO₄·H₂O的首次结构转变是明显的铁弹性P2₁/c - P1̅转变。从结构角度来看，它纯粹是位移型的，伴随着氢键方案的对称性变化。第二次从β-NiSO₄·H₂O到γ-NiSO₄·H₂O的转变，进一步分裂了O2（氢键受体）位置并违反了P1̅空间群对称性，从拉曼光谱中各个谱带的分裂也可以明显看出。这可以归因于通过局部违反局部中心对称性导致的对称性降低。通过将二阶Birch-Murnaghan状态方程拟合到体积 - 压力数据点获得晶格弹性，得到以下零压力体模量值：α-NiSO₄·H₂O为63.4 ± 1.0 GPa，β-NiSO₄·H₂O为61.3 ± 1.9 GPa，γ-NiSO₄·H₂O为68.8 ± 2.5 GPa。
