A. Rabenau

Re-evaluation of the lithium nitride structure

Abstract The crystal structure of Li 3 N was determined using single crystals obtained from the reaction of N 2 with liquid lithium. The proposed structure of Zintl and Brauer could be confirmed. Li 3 N is hexagonal: a = 3.648(1) A , c = 3.875(1) A , Z = 1. The space group was determined to be p 6/ mmm . The structure was refined, with anisotropic temperature factors, to R = 0.025 and R ( w ) = 0.026.

Lithium nitride and related materials case study of the use of modern solid state research techniques

Abstract Lithium nitride is a solid electrolyte with a high Li + -conductivity at ambient temperatures and attractive properties for an application in a primary battery. The proposed presence of a polarizable ion N 3- in the unique hexagonal structure could be proved by measurements of Czochralski-grown single crystals applying the methods of modern solid state science, particular X-ray diffraction. A model for the conduction mechanism of the Li + -ions is presented. Using crystal-chemical considerations a material for application at higher temperatures could be found among the lithium-nitride-halides.

Proton transport in some heteropolyacidhydrates a single crystal PFG-NMR and conductivity study

Single crystals of H3PW12O40·28H2O, H3PW12O40·21H2O and H4SiW12O40·28H2O have been prepared. The proton diffusion coefficients and conductivities have been determined for the pure protonic as for partially deuterated samples. The numbers are found to be lower than reported in the literature, the Nernst-Einstein relationship is fulfilled and there is almost no isotopic effect. The results indicate the vehicle-mechanism as the operating proton conduction mechanism instead of the Grotthuss mechanism as frequently suggested.

Li3FeN2, a ternary nitride with ∞1[FeN4/23-]-chains: Crystal structure and magnetic properties

Abstract Li3FeN2 was prepared from the melt under nitrogen and the crystal structure was determined by single-crystal diffraction (Ibam; a = 487.2(1) pm, b = 964.1(2) pm, c = 479.2(1) pm, Z = 4). The crystal structure can be described in terms of a fluorite superstructure which contains infinite chains 1 ∞ [FeN 4 2 3−] of edge-sharing FeN4 tetrahedra. Measurements of the magnetic susceptibilities vs. temperature reveal Curie-Weiss behaviour. Magnetic ordering occurs below 10 K. The calculated magnetic moment of 1.7(1) μB indicates a low spin state of the Fe3+ ion.

Proton conduction in zeolites

Abstract Protonic conduction in zeolites is optimized. The approach is based on a vehicle-mechanism for the transport process. The parameters controlling protonic conduction are discussed. Fully hydrated “NH 4 -zeolite A” has a room temperature conductivity of 2×10 −3 Ω −1 cm −1 . The material was successfully used in oxygen concentration cells (e.g. MnO 2 /NH 4 -zeolite A/Zn).

Investigation of proton-conducting solids

Abstract One-dimensional bulk proton conduction parallel to the c axis was observed in solid lithium hydrazinium sulfate, LiN 2 H 5 SO 4 . The conductivity in this direction is 2 × 10 −8 ω −1 cm −1 at 25°C and shows an activation enthalpy of 0.75 ± 0.07 eV. The two-dimensional conductors HUO 2 AsO 4 ·4H 2 O and HUO 2 PO 4 ·4H 2 O were studied as a function of their water content. The conductivities are 8 × 10 −6 and 3 × 10 −5 ω −1 cm −1 in the orthorhombic phase at −10°C, with activation enthalpies of 0.70 ± 0.05 and 0.57 ± 0.07 eV, respectively. Indications of peritectic transitions to the tetragonal phases were observed in the temperature ranges 15 to 47 and −5 to 10°C, respectively. The transition depends on the water content which appears to control the increase in conductivity in this material. The dependence upon various sample parameters is discussed. Fast proton transport in solids is proposed to occur by a “vehicle mechanism”, i.e. the motion of N 2 H + 5 , H 3 O + - or other proton-containing groups.

Preparation of highly oriented polycrystalline YBa2−y Cu3Ox superconductors

Abstract A simple processing technique for preparing highly oriented superconducting (BaO-deficient) YBaCu-ceramic is described. The maximum preparation temperature is 950°C. For that purpose small amounts of BaO (with respect to the 1:2:3 composition) are replaced by K 2 CO 3 in equimolar amounts or in excess of that. In this way a BaO-deficient material is obtained. The amount of potassium initially introduced is negligible after the process. The T c — value obtained is 94 K. The material consists of extremely oriented grains (only (001) — reflexes in the X-ray diffractogram). The so-prepared material is much more stable against humid atmosphere and need not be annealed again in air or oxygen. This procedure can also be extended to analogous superconductors (e.g. in the BiCaSrCuO system).

On the crystal structure of Ba8Ni6N7, a low valency nitridon1ccolate with infinite helical [Ni-N] zigzag chains

Abstract Ba8Ni6N7 was prepared from mixtures (pressed pellets) of BaNiN and Ba3N2 (molar ratio 1:1) at 800 °C under nitrogen. The crystal structure was determined by single-crystal X-ray diffraction ( C2 c ; a = 948.7(4) pm, b = 1657.8(6) pm, c = 1213.7(7) pm; β = 107.05(5)°; Z = 4). The rather complex new structure type is generated by distorted nitrogen coordination octahedra (NBa6, NBa4Ni2(cis) and NBa4Ni2(trans)) which share common edges as well as common corners. Barium is in a threefold (trig, planar) and a fourfold (distorted tetrahedral) nitrogen environment. Nickel (nearly linear coordination, N-Ni-N angle: 162.4(5)°–176.4(4)dg) and nitrogen (distance Ni[2]-N[6]: 175.6(10)–181.0(14) pm) are arranged to form infinite helical [Ni-N] zigzag chains which run parallel to the c ∗ direction.

Ternary and quaternary metal-nitrides in the Li-Sr-Ni-N-system

Abstract Single crystals of ternary and quaternary phases of the Li-Sr-Ni-N-system were grown from the melt under nitrogen and were investigated by X-ray diffraction methods. The crystal structures are classified into the following groups: i. solid solutions (substitutional type) of the Li 3 N-structure (Li 1−x Ni x [Li 2 N]), ii. structures containing fragments of the Li 3 N-structure (Li 4 SrN 2 , LiSrN and Li 4 Sr 2 (Li 0.8 .Ni 0.2 )N 3 and iii- structures which can be derived from interstitial binary metal nitrides of the first transition series (Li 3 Sr 3 Ni 4 N 4 ). The crystal structure of SrNiN is not quite clear at present, but shows close relations to the crystal structure of BaNiN (Sr(Ni 1−x Li x )N, resp.).

Dissociation pressure and Gibbs energy of formation of Y3Fe5O12 and YFeO3

Compounds in the ternary system Y--Fe--O are of significant interest due to their magnetic properties. Electrochemical solid state galvanic cell techniques have been employed to study their thermodynamic properties in the temperature range from 900 to 1250/sup 0/C. The following oxygen dissociation pressures were obtained: log p/sub O/sub 2// (Pa) = -26365/T + 17.13 for yttrium iron garnet, Y/sub 3/Fe/sub 5/O/sub 12/, in the entire temperature range, log p/sub O/sub 2// (Pa) = -29345/T + 13.00 for perovskite, YFeO/sub 3/, below 1080/sup 0/C and log p/sub O/sub 2// (Pa) = -39375/T + 20.43 for YFeO/sub 3/ above 1080/sup 0/C. The standard Gibbs energies of formation from metallic iron, yttria (Y/sub 2/O/sub 3/) and oxygen were determined to be ..delta..G/sup 0/ = -2078.2 + 0.5850 T kJ/mol for the formation of Y/sub 3/Fe/sub 5/O/sub 12/ and ..delta..G/sup 0/ = -421.3 + 0.1148 T kJ/mol for the formation of YFeO/sub 3/. The standard enthalpies and entropies of formation are -2078.2 kJ/mol and -585.0 J/mol K for Y/sub 3/Fe/sub 5/O/sub 12/ and -421.3 kJ/mol and -114.8 J/mol K for YFeO/sub 3/, respectively.