New calcium germanium nitrides: Ca2GeN2, Ca4GeN4, and Ca5Ge2N6

Building Nitridic Networks with Phosphorus and Germanium-from GeIIP2N4 to GeIVPN3

Nitridophosphates and nitridogermanates attract high interest in current research due to their structural versatility. Herein, the elastic properties of GeP2N4 were investigated by single-crystal X-ray diffraction (XRD) upon compression to 44.4(1) GPa in a diamond anvil cell. Its isothermal bulk modulus was determined to be 82(6) GPa. At 44.4(1) GPa, laser heating resulted in the formation of multiple crystalline phases, one of which was identified as unprecedented germanium nitridophosphate GePN3. Its structure was elucidated from single-crystal XRD data (C2/c (no. 15), a = 8.666(5), b = 8.076(4), c = 4.691(2) Å, β = 101.00(7)°) and is built up from layers of GeN6 octahedra and PN4 tetrahedra. The GeN6 octahedra form double zigzag chains, while the PN4 tetrahedra are found in single zigzag chains. GePN3 can be recovered to ambient conditions with a unit cell volume increase of about 12%. It combines PV and GeIV in a condensed nitridic network for the first time.

The Reduced Nitridogermanates(III) Ca6 [Ge2 N6 ] and Sr6 [Ge2 N6 ] with Ge-Ge Bonds

The first nitridogermanates(III) Ca₆[Ge₂N₆] and Sr₆[Ge₂N₆] were synthesized from sodium flux and structurally characterized by powder and single crystal X‐ray diffraction, respectively. They crystallize isostructurally to each other and homeotypic to Ca₆[Cr₂N₆]H in space group R3‾ . They feature unprecedented, mutually isolated, ethane‐like [Ge^III₂N₆]¹²⁻ anions in a staggered conformation. The compounds are semiconductors according to resistivity measurements and electronic structure calculations, yielding band gaps of 1.1 eV for Ca₆[Ge₂N₆] and 0.2 eV for Sr₆[Ge₂N₆].

Down-Conversion Nitride Materials for Solid State Lighting: Recent Advances and Perspectives

Advances in solid state white lighting technologies witness the explosive development of phosphor materials (down-conversion luminescent materials). A large amount of evidence has demonstrated the revolutionary role of the emerging nitride phosphors in producing superior white light-emitting diodes for lighting and display applications. The structural and compositional versatility together with the unique local coordination environments enable nitride materials to have compelling luminescent properties such as abundant emission colors, controllable photoluminescence spectra, high conversion efficiency, and small thermal quenching/degradation. Here, we summarize the state-of-art progress on this novel family of luminescent materials and discuss the topics of materials discovery, crystal chemistry, structure-related luminescence, temperature-dependent luminescence, and spectral tailoring. We also overview different types of nitride phosphors and their applications in solid state lighting, including general illumination, backlighting, and laser-driven lighting. Finally, the challenges and outlooks in this type of promising down-conversion materials are highlighted.

Nitridogermanate nitrides Sr7[GeN4]N2 and Ca7[GeN4]N2: synthesis employing sodium melts, crystal structure, and density-functional theory calculations

The alkaline earth nitridogermanate nitrides AE(7)[GeN(4)]N(2) (AE = Ca, Sr) have been synthesized using a Na flux technique in sealed Ta tubes. According to single-crystal X-ray diffraction the isotypic compounds crystallize in space group Pbcn (No. 60) with Z = 4, (Sr(7)[GeN(4)]N(2): a = 1152.6(2), b = 658.66(13), c = 1383.6(3) pm, V = 1050.5(4) x 10(6) pm(3), R1 = 0.049; Ca(7)[GeN(4)]N(2): a = 1082.6(2), b = 619.40(12), c = 1312.1(3) pm, V = 879.8(3) x 10(6) pm(3), R1 = 0.016). Owing to the high N/Ge ratio, the compounds contain discrete N(3-) ions coordinated by six AE(2+) besides discrete [GeN(4)](8-) tetrahedrons. One of the AE(2+) ion is coordinated by only four N(3-) ions, which is rather an unusual low coordination number for Sr(2+). Together with the isolated [GeN(4)](8-) tetrahedrons, these Sr(2+) ions form chains of alternating cation centered edge sharing tetrahedrons. The electronic structure and chemical bonding in Sr(7)[GeN(4)]N(2) has been analyzed employing linear muffin-tin orbital (LMTO) band structure calculations.

Sr11Ge4N6: a new nitride composed of [GeN2Sr7]4+ antiperovskite-type slabs and [Sr4Ge]4+ layers, separated by sheets of bent [Ge(II)N2]4- ions

The layered nitride Sr11Ge4N6 contains Ge4- Zintl anions in both [Sr4Ge]4+ layers and [GeN2Sr7]4+ antiperovskite-type slabs which are separated by sheets of bent [Ge(II)N2]4- ions; the observed range of formal germanium oxidation states in nitrides thus extends between +4 and -4.

Synthesis and structure of Sr3GaN3 and Sr6GaN5: strontium gallium nitrides with isolated planar [GaN3]6- anions

Two new strontium gallium nitrides were obtained as single crystals by reaction in molten Na. Black Sr(3)GaN(3) is isostructural with its transition metal analogues, Sr(3)MnN(3), Ba(3)MnN(3), Sr(3)CrN(3), Ba(3)CrN(3), and Ba(3)FeN(3), and is the first example of a 313-ternary nitride containing only main group metals. It crystallizes in space group P6(3)/m (No. 176) with a = 7.584(2) A, c = 5.410(3) A, and Z = 2. Black Sr(6)GaN(5) is isostructural with Ca(6)GaN(5) and also with its transition metal analogues, Ca(6)MnN(5) and Ca(6)FeN(5). It crystallizes in space group P6(3)/mcm (No. 193) with a = 6.6667(6) A, c = 12.9999(17) A, and Z = 2. Both Ga compounds contain isolated planar [GaN(3)](6)(-) nitridometallate anions of D(3)(h)() symmetry.

Possible nonactivated conductivity of the low-dimensional ternary nitride Ca(2)GeN(2)

The electronic structure of the recently reported ternary nitride Ca(2)GeN(2) has been studied by means of first-principles density functional calculations. The relatively short nonbonded Ge...Ge contacts along the direction approximately perpendicular to the plane of the bent GeN(2) units confer a large dispersion to the energy bands based on the antibonding pi-type level of GeN(2). This feature as well as the smaller but non-negligible interactions along the perpendicular directions suggests that this material, despite being built from discrete units, may exhibit a metallic behavior. This study suggests that the nature of the alkaline-earth atom has a crucial influence on the electrical conductivity of this type of phase.