Zur Kenntnis von Ordnungsvarianten des NaCl-Typs am Beispiel ternärer Oxide AMO2

On Ordered Variants of the NaCl Type of Structure on the Example of Ternary Oxides AMO₂ Possible ordered distributions of cations (A⁺ and M³⁺) on octahedral sites of a cubic closest packing of oxygen atoms are discussed. Limiting conditions are: ratio A⁺/M³⁺ equals 1; the surroundings of the different cations must be equivalent considering the anions as well as the cations. The Madelung Part of Lattice Energy, MAPLE, is calculated and discussed for all different possibilities with respect to “long range order” of the cations.     

Einkristalle von Ba[NiF6]

Single Crystals of Ba[NiF₆] Transparent, rubin-red single crystals of β-BaNiF₆ were grown unexpectedly by high pressure fluorination [pF₂ > 3500 atm, 450–500°C, 10d; Monel autoclave]. The refinement of the structure [Four circle diffractometer PW 1100, Mo^?Kα; 132 I₀(hkl) 3° < θ < 30°; anisotropic factors of temperature, R = R_W = 3.7%] confirmes the interpretation of powder datas due to them the BaGeF₆ type of structure is present.     

Limit theorems for the critical age-dependent branching process with infinite variance

Let Z(t) be the population at time t of a critical age-dependent branching process. Suppose that the offspring distribution has a generating function of the form f(s) = s + (1 ? s)^1+αL(1 ? s) where α ∈ (0, 1) and L(x) varies slowly as x → 0⁺. Then we find, as t → ∞, (P{Z(t)> 0})^αL(P{Z(t)>0})～ μ/αt where μ is the mean lifetime of each particle. Furthermore, if we condition the process on non-extinction at time t, the random variable P{Z(t)>0}Z(t) converges in law to a random variable with Laplace-Stieltjes transform 1 - u(1 + u^α)^?1/α for u ?/ 0. Moment conditions on the lifetime distribution required for the above results are discussed.     

The Coordination Number – an “Inorganic Chameleon”

The purpose of the present article is to describe the changing ambiguous character of the term “coordination number” and its present-day definition in structural chemistry, particularly of typical solids (assemblies of particles with short-range and long-range order). An effort is made at the same time to describe the crystal structure of solids as simply as possible while also taking long-range order into account, i.e. by determining “effective” coordination numbers by the geometrical “polyhedron method” or from MAPLE (Madelung Part of Lattice Energy) values.     

Unerwartete Strukturverwandtschaft: Das neue Orthotitanat Rb3Na[TiO4]

On Unexpected Structural Relations: The New Orthotitanate Rb₃Na[TiO₄] [1] The new oxide Rb₃Na[TiO₄], platelike colourless crystals, was obtained by heating a well grounded mixture of the binary oxides in Ni-tubes. Therewith the oxides RbO_0.52, NaO_1.03, Ti₂O₃ (Rb:Na:Ti = 2.8:2.5:1.0) were heated for 26 d at 1000°C. Rb₃Na[TiO₄] (monoclinic, P2₁/c) is “isostructural” with Rb₃Na[PbO₄] [2] (lattice constants: a = 1076.3(3) pm, b = 638.8(4) pm, c = 1088.9(7) pm, β = 112.83(12)°; four-circle diffractometer data, Z = 4). The structure was determinated by using four-circle diffractometer data (Siemens AED2, 6683 I₀(hkl), MoKα , R = 6.2%, R_w = 3.8%, additional data see text). The Madelung Part of Lattice Energy (MAPLE), Effective Coordination Numbers (ECoN), Mean Fictive Ionic Radii (MEFIR) and the Charge Distribution in Solids are calculated and discussed.     

Neue Borate der Alkalimetalle: KLi2[BO3]

New Borates of the Alkali Metals: KLi₂[BO₃] The hitherto unknown KLi₂[BO₃] is prepared in the shape of orthorhombic, colour-less-transparent, and columnar single crystals [a = 797.1(4) pm, b = 643.2(3) pm, c = 645.7(3) pm, Z = 4, d_x = 2.25 g/cm³, d_pyk = 2.20g/cm³]. The crystal structure was solved by four-cycle-diffractometer [PW 1100, MoKα, R = 5.78%, R_W = 3.83%, 452 I₀(hkl)]. Kli₂[BO₃] is sensitiv against atmospheric moisture which causes hydrolysis. Effective Coordination Numbers, ECoN, these via Mean Effective Ionic Radii, MEFIR, are calculated and discussed.     

Silver Halide and Silver Chalcogenide Systems. IV. Excess enthalpies of the liquid mixtures of AgCl + Ag2Se,Agl + Ag2Se,AgCl + Ag2Te,AgBr + Ag2Te,and Agl + Ag2Te

The integral enthalpies of mixing of the liquid mixtures AgCl + Ag₂Se, AgI + Ag₂Se, AgCl + Ag₂Te, AgBr + Ag₂Te and AgI + Ag₂Te were determined in an isoperibolic calorimeter. The systems have endothermic effects which can be explained by a misfit energy, due to the substitution of ions of different size in the polymeric network of these melts.