Growth of Chlorapatite Crystals from a Sodium Chloride Flux

Well-formed crystals of chlorapatite [Ca5Cl(PO4)3] were first grown from a sodium chloride flux. The solubility of Ca5Cl(PO4)3 in NaCl increased with increasing temperature. At 1100 °C, Ca5Cl(PO4)3 had a solubility of about 0.15 mol%. The crystal growth of Ca5Cl(PO4)3 was conducted by heating a mixture of solute and flux at 1100 °C for 10 h, followed by cooling to 500 °C at a rate of 5 °C h−1. Colorless and transparent crystals having lengths up to 4.0 mm and widths of 1.2 mm were grown from high-temperature solutions containing small amounts of solute (0.05—0.5 mol%). The obtained crystals were divided into two distinct morphological types: prisms and needles. The most suitable solute contents for the growth of prismatic and needle crystals were 0.15 and 0.1 mol%, respectively. The crystal forms were also dependent on the solute content. The prismatic crystals were bounded by the {} and {} faces. The needle crystals elongated in the <0001> directions. Calcium, chlorine, phosphorus, and oxygen were almost homogeneously distributed in the crystals.