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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 Pna2 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., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The phosphorus nitrides, Mg 2 PN 3 and Zn 2 PN 3 , are wide band gap semiconductor materials with potential for application in (opto)electronics or photovoltaics. For the first time, both compounds were synthesized ammonothermally in custom-built high-temperature, high-pressure autoclaves starting from P 3 N 5 and the corresponding metals (Mg or Zn). Alkali amides (NaNH 2 , KNH 2 ) were employed as ammonobasic mineralizers to increase solubility of the starting materials in supercritical ammonia through formation of reactive intermediates. Single crystals of Mg 2 PN 3 , with length up to 30 μm, were synthesized at 1070 K and 140 MPa. Zn 2 PN 3 already decomposes at these conditions and was obtained as submicron-sized crystallites at 800 K and 200 MPa. Both compounds crystallize in a wurtzite-type superstructure in orthorhombic space group Cmc2 1 , which was confirmed by powder X-ray diffraction. In addition, single-crystal X-ray diffraction measurements of Mg 2 PN 3 were carried out for the first time. To our knowledge, this is the first single-crystal X-ray study of ternary nitrides synthesized by the ammonothermal method. The band gaps of both nitrides were estimated to be 5.0 eV for Mg 2 PN 3 and 3.7 eV for Zn 2 PN 3 by diffuse reflectance spectroscopy. DFT calculations were carried out to verify the experimental values. Furthermore, a dissolution experiment was conducted to obtain insights into the crystallization behavior of Mg 2 PN 3 ., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Beryllate structures are marginally investigated, but show intriguing structural relations to oxo- and nitridosilicates. A typical feature is the coordination of Be in both trigonal planar and tetrahedral coordination by O. A broad range of structures is accessible by variable combinations of both building units. Three novel ternary Sr-oxoberyllates are characterized by single-crystal X-ray diffraction analysis, density functional theory calculations and investigations on luminescence properties: α-SrBeO 2 , β-SrBeO 2 and Sr 12 Be 17 O 29 are obtained with oxoberyllate substructures, made up of either BeO 3 triangles or BeO 4 tetrahedra. The compounds can be described as chain- and layer-type beryllates. When excited with blue light of (In,Ga)N LED chips, β-SrBeO 2 and Sr 12 Be 17 O 29 show visible emission in the yellow and orange spectral range, respectively, upon doping with Eu 2+ . Exceptional narrow-band yellow emission (λ em =564 nm, fwhm=55 nm) makes β-SrBeO 2 :Eu 2+ a promising phosphor for application in phosphor-converted (pc-)LEDs., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Grimm-Sommerfeld analogous nitrides MgSiN 2 , MgGeN 2 , MnSiN 2 , MnGeN 2 , LiSi 2 N 3 and LiGe 2 N 3 (generally classified as II-IV-N 2 and I-IV 2 -N 3 ) are promising semiconductor materials with great potential for application in (opto)electronics or photovoltaics. A new synthetic approach for these nitride materials was developed using supercritical ammonia as both solvent and nitride-forming agent. Syntheses were conducted in custom-built high-pressure autoclaves with alkali metal amides LiNH 2 , NaNH 2 or KNH 2 as ammonobasic mineralizers, which accomplish an adequate solubility of the starting materials and promote the formation of reactive intermediate species. The reactions were performed at temperatures between 870 and 1070 K and pressures up to 230 MPa. All studied compounds crystallize in wurtzite-derived superstructures with orthorhombic space groups Pna2 1 (II-IV-N 2 ) and Cmc2 1 (I-IV 2 -N 3 ), respectively, which was confirmed by powder X-ray diffraction. Optical bandgaps were estimated from diffuse reflectance spectra using the Kubelka-Munk function (MgSiN 2 : 4.8 eV, MgGeN 2 : 3.2 eV, MnSiN 2 : 3.5 eV, MnGeN 2 : 2.5 eV, LiSi 2 N 3 : 4.4 eV, LiGe 2 N 3 : 3.9 eV). Complementary DFT calculations were carried out to gain insight into the electronic band structures of these materials and to corroborate the optical measurements., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The high-pressure polymorph Li 5 P 2 N 5 of Li 10 P 4 N 10 (="2 Li 5 P 2 N 5 ") was synthesized by high-pressure/high-temperature reaction of LiPN 2 and Li 7 PN 4 or β-Li 10 P 4 N 10 at 9 GPa, using the Li 3 N self-flux method in a Walker-type multianvil assembly. Li 5 P 2 N 5 is the first lithium nitridophosphate with a layered structure and is made up of corner sharing PN 4 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 Li 5 P 2 N 5 as the corresponding high-pressure polymorph of β-Li 10 P 4 N 10 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., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Li 12 P 3 N 9 was synthesized by solid-state reaction of Li 3 N and P 3 N 5 at 790 °C. It is made up of non-condensed [P 3 N 9 ] 12- dreier-rings of PN 4 -tetrahedra. The corresponding high-pressure polymorph, Li 4 PN 3 , was synthesized under high-pressure/high-temperature conditions from Li 12 P 3 N 9 or LiPN 2 and Li 7 PN 4 at 6 or 7 GPa, respectively, using the multianvil technique. Li 4 PN 3 is the first lithium catena-nitridophosphate and contains PN 3 zweier-chains of corner sharing PN 4 -tetrahedra. To confirm the structure elucidated from single-crystal X-ray data, Rietveld refinement, 6 Li, 7 Li, and 31 P solid-state NMR spectroscopy, FTIR spectroscopy and EDX measurements were carried out. To examine the phase transition of Li 12 P 3 N 9 to Li 4 PN 3 at 6 GPa and to corroborate the latter as the corresponding high-pressure polymorph, DFT calculations were conducted. Electronic band gap and electron localization function (ELF) calculations were carried out to elucidate the electronic properties and bonding behavior of both polymorphs., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The first gallium-containing nitridosilicate CaGaSiN 3 was synthesized in newly developed high-pressure autoclaves using supercritical ammonia as solvent and nitriding agent. The reaction was conducted in an ammonobasic environment starting from intermetallic CaGaSi with NaN 3 as a mineralizer. At 770 K, intermediate compounds were obtained, which were subsequently converted to the crystalline nitride at temperatures up to 1070 K (70-150 MPa). The impact of other mineralizers (e.g., LiN 3 , KN 3 , and CsN 3 ) on the product formation was investigated as well. The crystal structure of CaGaSiN 3 was analyzed by powder X-ray diffraction and refined by the Rietveld method. The structural results were further corroborated by transmission electron microscopy, 29 Si MAS-NMR, and first-principle DFT calculations. CaGaSiN 3 crystallizes in the orthorhombic space group Cmc2 1 (no. 36) with lattice parameters a=9.8855(11), b=5.6595(1), c=5.0810(1) Å, (Z=4, R wp =0.0326), and is isostructural with CaAlSiN 3 (CASN). Eu 2+ doped samples exhibit red luminescence with an emission maximum of 620 nm and FWHM of 90 nm. Thus, CaGaSiN 3 :Eu 2+ also represents an interesting candidate as a red-emitting material in phosphor-converted light-emitting diodes (pc-LEDs). In addition to the already known substitution of alkaline-earth metals in (Ca,Sr)AlSiN 3 :Eu 2+ , inclusion of Ga is a further and promising perspective for luminescence tuning of widely used red-emitting CASN type materials., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)