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The Crystal Structure of Pb10(PO4)6O Revisited: The Evidence of Superstructure
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: Received: 9 August 2023 / Approved: 9 August 2023 / Online: 10 August 2023 (02:26:03 CEST)
A peer-reviewed article of this Preprint also exists.
Krivovichev, S.V.; Engel, G. The Crystal Structure of Pb10(PO4)6O Revisited: The Evidence of Superstructure. Crystals 2023, 13, 1371. Krivovichev, S.V.; Engel, G. The Crystal Structure of Pb10(PO4)6O Revisited: The Evidence of Superstructure. Crystals 2023, 13, 1371.
Abstract
The crystal structure of Pb10(PO4)6O, the proposed matrix for the potential room-temperature superconductor LK-99, Pb10-xCux(PO4)6O (x = 0.9-1.0), has been reinvestigated by single-crystal X-ray diffraction using crystals prepared by Merker and Wondratschek (The crystal structure is trigonal, P, a = 9.8109(6), c = 14.8403(12) Å, V = 1237.06(15), R1 = 0.0413 using 3456 unique observed reflections. The crystal structure of Pb10(PO4)6O is a superstructure with regard to the ‘standard’ P63/m apatite structure type. The doubling of the c parameter is induced by the ordering of ‘additional’ O’ atoms within the structure channels running parallel to the c axis and centered at (00z). The O’ atoms form short bonds to the Pb1 atoms, resulting in splitting the Pb1 site into two, Pb1A and Pb1B. The structural distortions are further transmitted to the Pb phosphate framework formed by four Pb2 sites and PO4 groups. The structure data previously reported by Krivovichev and Burns (Z. Kristallogr. 2003, 218, 357-365) may either correspond to the Pb10(PO4)6Ox(OH)2-x (x ~ 0.4) member of the Pb10(PO4)6O - Pb10(PO4)6(OH)2 solid solution series, or to the high-temperature polymorph of Pb10(PO4)6O (with the phase with doubled c parameter being the low-temperature polymorph).
Keywords
‘oxypyromorphite’; crystal structure; superconductivity; symmetry breaking; crystal structure; structural complexity
Subject
Physical Sciences, Condensed Matter Physics
Copyright: This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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