Hydrothermal synthesis of a novel non-stoichiometric cubic bismuth phosphate (Bi12(Bi4/5–5xP5x)O19.2 + 5x) crystal and the coexistence of multilevel Kink-Terrace-Step structures on Kossel (1 0 0) surface

• Pure cubic phase could be synthesized at high alkalinity.
• The height of the lowest kinked [0 1 0] steps was about half of the unit cell.
• Multilevel Kink-Terrace-Step structures coexisted on Kossel (1 0 0) surface.
• Multilevel growth units are PO4− incorporating into the channels of Bi–O frameworks.

Nonstoichiometric cubic bismuth phosphate crystals were synthesized and grown by hydrothermal method. Under high alkalinity condition, three dimensional nuclei were generated and combined into cubic plates. The cubic bismuth phosphate crystals were combined by the corresponding cubic plates with various defects and rough surfaces. The cubic plates made (1 0 0) surface of the crystal cleavage face. Additionally, multilevel Kink-Terrace-Step structures on Kossel (1 0 0) surface were characterized through scanning electron microscopy and atomic force microscope techniques, respectively. It revealed that the lowest level Kink-Terrace-Step structure was in nano-scale, and the height of the elemental kinked [0 1 0] steps was about half of the unit cell. The elemental kinked [0 1 0] steps could bunch together and consequently constructed a higher level of Kink-Terrace-Step structures. As a result, multilevel Kink-Terrace-Step structures coexisted on the Kossel (1 0 0) surface of bismuth phosphate crystal, which were owing to the coexistence of multilevel growth units in crystal growth system.

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