Solubility and local structure of transmission elements in calcium silicate compounds has not been well understood. We investigate the local structure of chromium ions dissolved in merwinite (3CaO·MgO·2SiO₂) of a monoclinic crystal structure. The acceptance of doping elements into merwinite has not been reported before. We found that chromium ions are soluble in merwinite in air and that chemical valence of the dissolved Cr ions varies with annealing temperature. The absorption edge in the x‐ray absorption near edge structure (XANES) of Cr‐doped merwinite indicated that octahedrally coordinated Cr³⁺ ions were mainly formed when annealed at 1673 K in air. A pre‐edge peak was also detected, indicating the existence of tetrahedrally coordinated high‐valence Cr ions. Conversely, through annealing of merwinite at 1123 K in air, tetrahedrally coordinated Cr⁶⁺ ions were found to be the main form of chromium. XANES spectra simulated by first‐principle calculations were used to explain the structural features in the observed spectra. We propose the coexistence of Cr³⁺ ions in octahedral Mg²⁺ sites and high‐valence Cr ions in tetrahedral Si⁴⁺ sites. In addition, a change in the chromium ion oxidation state in tetrahedral coordination sites was suggested by XANES spectroscopy of Cr‐doped merwinite synthesized at 1673 K and reannealed at 1123 K.

中文翻译：

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热历程对高价铬离子在褐铁矿（3CaO·MgO·2SiO2）中溶解的影响

硅酸钙化合物中传输元素的溶解度和局部结构尚未得到很好的理解。我们研究了铬在单斜晶体结构的（3CaO·MgO·2SiO ₂）中溶解的铬离子的局部结构。以前没有报道过将掺杂元素掺入光辉石中。我们发现铬离子可溶于空气中的绿沸石中，并且溶解的Cr离子的化学价随退火温度而变化。Cr掺杂的硫钨矿在X射线吸收附近边缘结构（XANES）中的吸收边缘表明八面体配位的Cr ³⁺离子主要是在1673 K的空气中退火时形成的。还检测到前边缘峰，表明存在四面配位的高价Cr离子。相反，通过在空气中1123 K的硫汞矿退火，发现四面体配位的Cr ⁶⁺离子是铬的主要形式。通过第一性原理计算模拟的XANES光谱用于解释观察到的光谱中的结构特征。我们提出八面体Mg ²⁺位点中Cr ³⁺离子与四面体Si ^4+中价态Cr离子共存网站。此外，XANES光谱表明，在1673 K时合成并在1123 K时再退火的铬掺杂的硫汞矿的四面体配位点中的铬离子氧化态发生了变化。