  Elemental phosphorus exhibits fascinating structural varieties and versatile
properties. The unique nature of phosphorus bonds can lead to the formation of
extremely complex structures, and detailed structural information on some
phosphorus polymorphs is yet to be investigated. In this study, we investigated
an unidentified crystalline phase of phosphorus, type-II red phosphorus (RP),
by combining state-of-the-art structural characterization techniques. Electron
diffraction tomography, atomic-resolution scanning transmission electron
microscopy (STEM), powder X-ray diffraction, and Raman spectroscopy were
concurrently used to elucidate the hidden structural motifs and their packing
in type-II RP. Electron diffraction tomography, performed using individual
crystalline nanowires, was used to identify a triclinic unit cell with volume
of 5330 {\AA}^3, the largest unit cell for elemental phosphorus crystals up to
now, which contains approximately 250 phosphorus atoms. Atomic-resolution STEM
imaging, which was performed along different crystal-zone axes, confirmed that
the twisted wavy tubular motif is the basic building block of type-II RP. Our
study discovered and presented a new variation of building blocks in
phosphorus, and it provides insights to clarify the complexities observed in
phosphorus as well as other relevant systems.
