Abstract Two polymorphs of Ln 2 P 3 N 7 (Ln: La, Ce, Pr, Nd, Sm, Eu, Ho, Yb) are prepared by solid state high‐pressure metathesis reactions of LiPN 2 , Li 3 N, and LnF 3 (900—1250 °C, 4—5 GPa, 20—360 min).

Melilite

Salt metathesis reaction

10.1002/chin.201648014

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Reversible Polymerization of Adamantane‐type [P₄N₁₀]¹⁰⁻ Anions to Honeycomb‐type [P₂N₅]⁵⁻ Layers under High‐Pressure

Chemistry - A European Journal (2017)

Eva‐Maria Bertschler Robin Niklaus Wolfgang Schnick

The high-pressure polymorph Li5 P2 N5 of Li10 P4 N10 (="2 Li5 P2 N5 ") was synthesized by high-pressure/high-temperature reaction of LiPN2 and Li7 PN4 or β-Li10 P4 N10 at 9 GPa, using the Li3 N self-flux method in a Walker-type multianvil assembly. Li5 P2 N5 is the first lithium nitridophosphate with a layered structure and is made up of corner sharing PN4 tetrahedra forming a corrugated honeycomb-type layer of linked sechser-rings in chair conformation. The arrangement of the P atoms is analogous to that of black phosphorus. The structure was elucidated from single-crystal X-ray data. To confirm the structure Rietveld refinement, 6 Li, 7 Li and 31 P solid-state NMR spectroscopy were conducted. To corroborate Li5 P2 N5 as the corresponding high-pressure polymorph of β-Li10 P4 N10 DFT calculations and temperature dependent X-ray powder diffraction were carried out. DFT calculations estimated the transition pressure to 6.5 GPa (without accounting for temperature), which is in line with the synthesis pressure.

Adamantane

Honeycomb

10.1002/chem.201704975

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Solid Solutions of Grimm–Sommerfeld Analogous Nitride Semiconductors II‐IV‐N₂ (II=Mg, Mn, Zn; IV=Si, Ge): Ammonothermal Synthesis and DFT Calculations

Chemistry - A European Journal (2019)

Mathias Mallmann Robin Niklaus Tobias Rackl Maximilian Benz Thanh Chau

Abstract Grimm–Sommerfeld analogous II‐IV‐N 2 nitrides such as ZnSiN 2 , ZnGeN 2 , and MgGeN 2 are promising semiconductor materials for substitution of commonly used (Al,Ga,In)N. Herein, the ammonothermal synthesis of solid solutions of II‐IV‐N 2 compounds (II=Mg, Mn, Zn; IV=Si, Ge) having the general formula (II a 1− x II b x )‐IV‐N 2 with x ≈0.5 and ab initio DFT calculations of their electronic and optical properties are presented. The ammonothermal reactions were conducted in custom‐built, high‐temperature, high‐pressure autoclaves by using the corresponding elements as starting materials. NaNH 2 and KNH 2 act as ammonobasic mineralizers that increase the solubility of the reactants in supercritical ammonia. Temperatures between 870 and 1070 K and pressures up to 200 MPa were chosen as reaction conditions. All solid solutions crystallize in wurtzite‐type superstructures with space group Pna 2 1 (no. 33), confirmed by powder XRD. The chemical compositions were analyzed by energy‐dispersive X‐ray spectroscopy. Diffuse reflectance spectroscopy was used for estimation of optical bandgaps of all compounds, which ranged from 2.6 to 3.5 eV (Ge compounds) and from 3.6 to 4.4 eV (Si compounds), and thus demonstrated bandgap tunability between the respective boundary phases. Experimental findings were corroborated by DFT calculations of the electronic structure of pseudorelaxed mixed‐occupancy structures by using the KKR+CPA approach.

Wurtzite crystal structure

10.1002/chem.201903897

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ChemInform Abstract: A High‐Pressure Polymorph of Phosphorus Oxonitride with the Coesite Structure.

ChemInform (2015)

Dominik Baumann Robin Niklaus Wolfgang Schnick

Abstract The title high‐pressure PON polymorph is obtained from cristobalite‐type PON by high‐temp, high‐pressure treatment (multianvil cell, 1300 °C, 15.5 GPa, 1 h).

Coesite

10.1002/chin.201524002

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Ammonothermal Crystal Growth of ATaN₂ with A = Na, K, Rb, and Cs and Their Optical and Electronic Properties

Crystal Growth & Design (2019)

Niklas Cordes Robin Niklaus Wolfgang Schnick

Crystals of alkali nitridotantalates, ATaN2 (A = Na, K, Rb, Cs), with well developed shape were grown from corresponding alkali amides or azides and elementary Ta in supercritical ammonia. The aforementioned alkali mineralizers provide an ammonobasic environment for crystal growth. Temperatures of up to 1070 K resulted in an internal pressure of up to 170 MPa in high-pressure custom-built autoclaves. For successful crystal growth, a custom-built Ta liner was used as substrate. The obtained ATaN2 crystals vary in size depending on the used alkali metal (Na, 50 μm; K, 40 μm; Rb, 200 μm; Cs, 50 μm). In addition, a second temperature step at the decomposition temperature of the respective mineralizer is required for the successful synthesis of crystals, due to formation of intermediates at lower temperatures. The obtained products were examined by PXRD, SEM, and UV–vis spectroscopy. The electronic properties were investigated by DFT calculations.

Crystal (programming language)

10.1021/acs.cgd.9b00357

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CSD 1791510: Experimental Crystal Structure Determination

The Cambridge Structural Database (2017)

Christine Poesl Robin Niklaus Wolfgang Schnick

10.25505/fiz.icsd.cc1y46ny

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