Abstract The investigation of the presence and role of sulfates in our solar system receives growing attention because these compounds play a crucial role in the water budget of planets such as Mars and significantly influence melting equilibria on the icy moons of Saturn and Jupiter, leading to the formation of subsurface oceans and even cryovolcanism. Despite the dominant presence of higher sulfate hydrates such as epsomite, MgSO4·7H2O, and mirabilite, Na2SO4·10H2O, on these moons’ surfaces, it is not excluded that lower-hydrated sulfates, such as kieserite, MgSO4·H2O, are also present, forming from higher hydrates under pressures relevant to the mantle of the icy moons. Given the composition of the soluble fraction in C1 and C2 chondritic meteorites, which are high in Ni content and also considered to represent the composition of the rocky cores of the Jovian icy moons, the actual compositions of potentially present monohydrate sulfates likely lie at intermediate values along the solid-solution series between kieserite and transition-metal kieserite-group end-members, incorporating Ni in particular. Moderate Ni contents are also probable in kieserite on Mars due to the planet’s long-term accumulation of meteoritic nickel, although likely to a much lesser extent than Fe. Structural and spectroscopic differences between the pure Mg- and Ni-end-members have been previously documented in the literature, but no detailed crystal chemical and spectroscopic investigation along the Mg-Ni solid solution has been done yet. The present work proves the existence of a continuous (Mg,Ni)SO4·H2O solid-solution series for the first time. It provides a detailed insight into the changes in lattice parameters, structural details, and positions of prominent bands in infrared (transmission, attenuated total reflectance, diffuse reflectance) and Raman spectra in synthetic samples as the Ni/Mg ratio progresses, at both ambient as well as low temperatures relevant for the icy moons and Mars. UV-Vis-NIR crystal field spectra of the Ni end-member also help to elucidate the influence of Ni2+-related bands on the overtone- and combination modes. The (Mg,Ni)SO4·H2O solid-solution series shows Vegard-type behavior, i.e., lattice parameters as well as spectral band positions, change along linear trends with increasing Ni content. Infrared spectra reveal significant changes in the wavenumber positions of prominent bands, depending on the Ni/Mg ratio. We show that the temperature during measurement also has an influence on band position, mainly in the case of H2O-related bands. The changes observed for several absorption features in the IR spectra enable rough estimation of the Ni/Mg ratio in the monohydrate sulfate, which is applicable to present and future remote sensing data, as well as in situ measurements on Mars or the icy moons. The spectral features most diagnostic of composition are the vibrational stretching modes of the H2O molecule and a band unique to kieserite-group compounds at around 900 cm–1 in the IR spectra, as well as the pronounced ν3 and ν1 sulfate stretching modes visible in Raman spectra.

中文翻译：

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在常温和低温下对镁橄榄石-钙镁铝石固溶体系列 (Mg,Ni)SO4·H2O 进行结构和光谱研究，对冰冷的卫星和火星具有宇宙化学意义

摘要 对太阳系中硫酸盐的存在和作用的研究受到越来越多的关注，因为这些化合物在火星等行星的水收支中起着至关重要的作用，并显着影响土星和木星冰卫星的融化平衡，导致地下海洋的形成甚至冰火山作用。尽管在这些卫星的表面上主要存在较高的硫酸盐水合物，如泻石 MgSO4·7H2O 和芒硝 Na2SO4·10H2O，但不排除低水合硫酸盐，如镁橄榄石，MgSO4·H2O，也存在，在与冰卫星的地幔有关的压力下由更高的水合物形成。鉴于 C1 和 C2 球粒陨石中可溶部分的组成，镍含量高，也被认为代表了木星冰卫星岩石核的组成，潜在存在的一水硫酸盐的实际组成可能位于沿着硅镁铝矿和过渡金属镁铝矿之间的固溶系列的中间值 -组最终成员，特别是包括 Ni。由于火星长期积累陨石镍，火星上的硅镁铝石中也可能含有中等镍含量，但其含量可能比铁小得多。纯 Mg 和 Ni 端部成员之间的结构和光谱差异先前已在文献中记录，但尚未进行沿 Mg-Ni 固溶体的详细晶体化学和光谱研究。目前的工作证明了连续 (Mg, Ni)SO4·H2O 固溶体系列首次。它提供了对合成样品中的晶格参数、结构细节和红外显着波段（透射、衰减全反射、漫反射）和拉曼光谱随着 Ni/Mg 比率的进展的变化的详细洞察，在环境和以及与冰冷的卫星和火星相关的低温。Ni 端元的 UV-Vis-NIR 晶体场光谱也有助于阐明 Ni2+ 相关波段对泛音和组合模式的影响。(Mg,Ni)SO4·H2O固溶体系列表现出Vegard型行为，即随着Ni含量的增加，晶格参数和谱带位置呈线性趋势变化。红外光谱揭示了显着波段波数位置的显着变化，取决于 Ni/Mg 的比例。我们表明，测量过程中的温度也对波段位置有影响，主要是在 H2O 相关波段的情况下。在红外光谱中观察到的几个吸收特征的变化能够粗略估计一水硫酸盐中的镍/镁比，这适用于现在和未来的遥感数据，以及火星或冰卫星的原位测量。最能诊断成分的光谱特征是 H2O 分子的振动拉伸模式和 IR 光谱中约 900 cm-1 处的硅镁铝石族化合物特有的带，以及显着的 ν3 和 ν1 硫酸盐拉伸模式在拉曼光谱中可见光谱。在红外光谱中观察到的几个吸收特征的变化能够粗略估计一水硫酸盐中的镍/镁比，这适用于现在和未来的遥感数据，以及火星或冰卫星的原位测量。最能诊断成分的光谱特征是 H2O 分子的振动拉伸模式和红外光谱中约 900 cm-1 处的硫酸镁铝石族化合物特有的带，以及显着的 ν3 和 ν1 硫酸盐拉伸模式在拉曼光谱中可见光谱。在红外光谱中观察到的几个吸收特征的变化能够粗略估计一水硫酸盐中的镍/镁比，这适用于现在和未来的遥感数据，以及火星或冰卫星的原位测量。最能诊断成分的光谱特征是 H2O 分子的振动拉伸模式和红外光谱中约 900 cm-1 处的硫酸镁铝石族化合物特有的带，以及显着的 ν3 和 ν1 硫酸盐拉伸模式在拉曼光谱中可见光谱。