Single crystal growth of Pb5(PxAs1−xO4)3Cl solid solution with apatite type structure

Using flux method with cesium chloride solvent, Pb5(PxAs1−xO4)3Cl single crystals were grown. Individual euhedral crystals consist of a hexagonal prism shape topped by a hexagonal pyramid, elongate [0 0 1] with a length-to-width ratio of approximately 1:5. These crystals were chemically homogeneous and exhibited no compositional zoning of P and As. Stopping the N2 supply into the electric furnace during heating and growth formed pale yellow crystals together with colorless transparent crystals. These materials display identical X-ray powder patterns and infrared absorption spectra. Furthermore, no marked difference is apparent in the chemical compositions of colorless crystals and yellow ones. A relationship to color development is apparent in an O 1s binding energy in XPS measurements. The O 1s binding energy is higher for strongly colored crystals, and that for yellow crystals can shift from 530.65 to 530.73 eV depending on the degree of color development. The O 1s binding energies for naturally occurring green pyromorphite and yellow mimetite were greatly enhanced respectively to 531.44 and 531.11 eV. This color development process of materials reflects the environmental concentration of oxygen during its crystallization.