Puzzling Intergrowth in Cerium Nitridophosphate Unraveled by Joint Venture of Aberration-Corrected Scanning Transmission Electron Microscopy and Synchrotron Diffraction

Abstract

Thorough investigation of nitridophosphates has rapidly accelerated through development of new synthesis strategies. Here we used the recently developed high-pressure metathesis to prepare the first rare-earth metal nitridophosphate, CeLiPN, with a high degree of condensation >1/2. CeLiPN consists of an unprecedented hexagonal framework of PN tetrahedra and exhibits blue luminescence peaking at 455 nm. Transmission electron microscopy (TEM) revealed two intergrown domains with slight structural and compositional variations. One domain type shows extremely weak superstructure phenomena revealed by atomic-resolution scanning TEM (STEM) and single-crystal diffraction using synchrotron radiation. The corresponding superstructure involves a modulated displacement of Ce atoms in channels of tetrahedra 6-rings. The displacement model was refined in a supercell as well as in an equivalent commensurate (3 + 2)-dimensional description in superspace group P6(α, β, 0)0(-α - β, α, 0)0. In the second domain type, STEM revealed disordered vacancies of the same Ce atoms that were modulated in the first domain type, leading to sum formula CeLiPNO (x ≈ 0.72) of the average structure. The examination of these structural intricacies may indicate the detection limit of synchrotron diffraction and TEM. We discuss the occurrence of either Ce displacements or Ce vacancies that induce the incorporation of O as necessary stabilization of the crystal structure.

Open‐Shell 3d Transition Metal Nitridophosphates MIIP8N14 (MII=Fe, Co, Ni) by High‐Pressure Metathesis

“…The formed lithium halide is the thermodynamic driving force of the exothermic reaction and flux medium enhancing the growth of single crystals . By addition of nitrides or oxides like Li 3 N, P 3 N 5 , Li 2 O, PON, or P 2 O 5 to this route, a systematic access to rare‐earth nitridophosphates has been established resulting in compounds with structural motifs ranging from highly condensed frameworks (e.g., Ce 4 Li 3 P 18 N 35 ) down to non‐condensed tetrahedra (e.g., Ho 3 [PN 4 ]O) …”

SrH4P6N12 and SrP8N14: Insights into the Condensation Mechanism of Nitridophosphates under High Pressure

“…[5,10] Furthermore, calculations predicted the existence of afurtherhigh-pressure polymorph, d'-P 3 N 5 ,exhibiting trigonal bipyramids as fivefold coordination spheres of P, as well as sixfold coordinated Pi na no ctahedral environment. [23][24][25][26] Despite multiple synthetic approaches and the gradually increasingn umber of compounds,i nformationa bout their formation mechanism is limited to the assumptiont hat precursor fragments with preferred anions, like three-and four-memberedr ings, might serve as buildingu nits durings yntheses. [12,13] Due to the fact that the typically-used starting materials, like P 3 N 5 ,a re temperatures ensitivea bove 850 8C, but even higher temperatures are needed for reversible PÀNb ond rearrangements,t he multianvil technique has been successfully employedf or syntheses of (imido)nitridophosphates in order to suppress the formation of N 2 by thermal dissociation.…”

“…Thereby, alkali, alkaline earth, and transition metals have been introduced into P/N‐based networks . Recently, high‐pressure metathesis has been established as another promising approach for rare‐earth metal nitridophosphates …”

The Long‐Periodic Loop‐Branched Chain Structure of the Oxonitridophosphate La21P40O46N57, Elucidated by a Combination of TEM and Microfocused Synchrotron Radiation

“…However, high‐pressure metathesis has been shown to be a successful approach to rare‐earth nitridophosphates . The presence of hydrolysis products during high‐pressure synthesis has, for example, led to the complex intergrown structure of Ce 4−0.5 x Li 3 P 18 N 35−1.5 x O 1.5 x ( x ≈0.72) …”