Manganese phosphate hydrate crystals were prepared from aqueous solutions containing MnCl₂, (NH₄)₂HPO₄, and citric acid. Switzerite [Mn₃(PO₄)₂·7H₂O] and niahite (NH₄MnPO₄·H₂O) phases were produced at room temperature, and then, hureaulite [Mn₅(PO₃OH)₂(PO₄)₂·4H₂O] particles were obtained by aging at 80 °C or by hydrothermal treatment at 100–180 °C. The lower aging temperature (80 °C) and the chelation of Mn²⁺ ions by citric acid provided a slower crystal growth, resulting in large hexagonal prism blocks of ca. 500 μm in size. These were found to be single crystals of hureaulite by powder and single-crystal X-ray diffraction analysis. Diffuse reflectance spectroscopy and evaluation using L*a*b* color parameters indicated that the large single crystals present a vivid pink color and high transparency.

中文翻译：

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用于制备无机颜料材料的磷酸锰水合物晶体的水相合成

磷酸锰水合物晶体由含有 MnCl ₂、(NH ₄ ) ₂ HPO ₄和柠檬酸的水溶液制备。Switzerite [Mn ₃ (PO ₄ ) ₂ ·7H ₂ O] 和niahite (NH ₄ MnPO ₄ ·H ₂ O) 相在室温下生成，然后，hureaulite [Mn ₅ (PO ₃ OH) ₂ (PO ₄ ) ₂ ·4H ₂O] 颗粒是通过在 80°C 下老化或在 100-180°C 下进行水热处理而获得的。较低的老化温度 (80 °C) 和柠檬酸对 Mn ²⁺离子的螯合提供了较慢的晶体生长，从而产生了约 500 微米大小。通过粉末和单晶X-射线衍射分析发现这些是纯辉长石的单晶。漫反射光谱和使用L * a * b * 颜色参数的评估表明大单晶呈现鲜艳的粉红色和高透明度。