Electronic structure and physical properties of the spinel-type phase of BeP2N4 from all-electron density functional calculations

Using density-functional-theory-based ab initio methods, the electronic structure and physical properties of the newly synthesized nitride BeP2N4 with a phenakite-type structure and the predicted high-pressure spinel phase of BeP2N4 are studied in detail. It is shown that both polymorphs are wide band-gap semiconductors with relatively small electron effective masses at the conduction-band minima. The spinel-type phase is more covalently bonded due to the increased number of P-N bonds for P at the octahedral sites. Calculations of mechanical properties indicate that the spinel-type polymorph is a promising superhard material with notably large bulk, shear, and Young’s moduli. Also calculated are the Be K, P K, P L3, and N K edges of the electron energy-loss near-edge structure for both phases. They show marked differences because of the different local environments of the atoms in the two crystalline polymorphs. These differences will be very useful for the experimental identification of the products of high-pressure syntheses targeting the predicted spinel-type phase of BeP2N4

Alkaline earth metal nitride compounds with the composition M2NX (M = Ca, Sr, Ba; X = ☐, H, Cl or Br)

The alkaline earth metal nitride compounds Ca2N, Sr2N, (Sr0.48Ba0.52)(2)N, Ba2N, Sr2NCl and Sr2NBr have been synthesized and investigated by the means of X-ray diffraction. These compounds all have crystal structures closely related to the anti-alpha-NaFeO2 Structure type. The reaction products obtained from the nominal starting compositions "Ca2NHx" (0 less than or equal to x less than or equal to 1) were also analyzed by X-ray powder diffraction. With x greater than or equal to 0.75, Ca2NH1-delta is the only product observed, but for x < 0.75, Ca2N is found in equilibrium with Ca2NH1-δ. An overview Of M2NX and alkaline earth metal subnitride compounds compares the present results to literature data. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved

The cluster azides M2[Nb6Cl12(N3)6]·(H2O)4-x (M = Ca, Sr, Ba)

The isotypic cluster compounds M-2[Nb6Cl12(N-3)(6)] . (H2O)(4- x) (M = Ca (1), M = Sr (2) and M = Ba (3)) have been synthesized by the reaction of an aequeous solution of Nb6Cl14 with M(N-3)(2), 1, 2 and 3 crystallize in the space group Fd(3) over bar (No. 227) with the lattice constants a = 1990.03(23), 2015.60(12) and 2043,64(11)pm, respectively. All compounds contain isolated 16e(-) clusters whose terminal positions are all occupied by orientationally disordered azide ligands