Abstract The crystal structure of hibonite with an ideal formula CaAl12O19 is hexagonal P63/mmc, isostructural with magnetoplumbite. Natural and synthetic hibonites have been widely studied for their formation, compositions, crystal structures, properties and applications. Recent increasing interest in its coloration has led to the search of inorganic pigments based on the hibonite structure. We present here the syntheses and characterization of hibonite compounds with a general formula of AAl12−xMxO19 (A = Ca, Sr, RE (rare earths) or any combination thereof; and M = Ni or Ni coupled with one of the following: Ti, Sn, Ge, Nb, Ta, Sb). Bright sky-blue to royal-blue colors are induced in these oxides prepared by conventional solid state reactions, as demonstrated in the solid solutions of CaAl12−2xNixTixO19 (x = 0–1) and Ca1−xLaxAl12−xNixO19 (x = 0–1). The values of color coordinates L*a*b* range from 64.5, −5.3, −18.5 to 57, −11.33, −30.38. Structure refinements of neutron powder diffraction data reveal that Ni preferably occupies the tetrahedral site in the hibonite structure, and magnetic susceptibility analysis confirms that this Ni is Ni2+. Optical measurements further verify that the observed blue color is due to d-d transitions of tetrahedral Ni2+. The preference of Ni2+ for the tetrahedral site is unusual because Ni2+ prefers the octahedral site in the spinel NiAl2O4. We attribute this unexpected behavior to the unusually large Al−O distances for the tetrahedral site in the hibonite structure. These blue hibonites exhibit excellent thermal stability, superior acid/base durability and better near-infrared reflectance than that of the commercial cobalt blue pigment. Our results suggest a potential route to the development of inexpensive, enduring and cobalt-free blue pigments. Synthesis and characterization methods are briefly reviewed for hibonite type of oxides, especially those with blue colors.

中文翻译：

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具有黑碳石结构的有色氧化物：非钴蓝色颜料的潜在途径

摘要 理想分子式为CaAl12O19 的黑碳石的晶体结构为六方P63/mmc，与磁铅石同构。天然和合成的黑碳石因其形成、成分、晶体结构、性质和应用而被广泛研究。最近对其着色的兴趣日益增加，促使人们开始寻找基于黑碳石结构的无机颜料。我们在此展示了具有通式 AAl12-xMxO19（A = Ca、Sr、RE（稀土）或其任意组合；并且 M = Ni 或 Ni 与以下之一结合的黑硼石化合物的合成和表征：Ti、 Sn、Ge、Nb、Ta、Sb)。在这些通过常规固态反应制备的氧化物中诱导出明亮的天蓝色到品蓝色，如 CaAl12−2xNixTixO19 (x = 0–1) 和 Ca1−xLaxAl12−xNixO19 (x = 0–1) 的固溶体所示。颜色坐标 L*a*b* 的值范围从 64.5、-5.3、-18.5 到 57、-11.33、-30.38。中子粉末衍射数据的结构精修表明，Ni 优先占据黑磷矿结构中的四面体位点，磁化率分析证实该 Ni 是 Ni2+。光学测量进一步证实观察到的蓝色是由于四面体 Ni2+ 的 dd 跃迁。Ni2+ 偏爱四面体位点是不寻常的，因为 Ni2+ 偏爱尖晶石 NiAl2O4 中的八面体位点。我们将这种意外行为归因于黑曜石结构中四面体位点的异常大的 Al-O 距离。这些蓝色黑炭黑具有优异的热稳定性，与商业钴蓝颜料相比，具有优异的酸/碱耐久性和更好的近红外反射率。我们的研究结果表明了开发廉价、持久和无钴蓝色颜料的潜在途径。简要回顾了黑铁矿型氧化物的合成和表征方法，特别是那些具有蓝色的氧化物。