W. Gunsser

Structure and electrical conductivity of TCNQ-2,3,7,8-tetramethoxychalcogenanthrene complexes

Abstract Charge-transfer complexes formed by reaction of 2,3,7,8-tetramethoxychalcogenanthrenes(5,10-dichalcogenacyclo-diveratrylenes, ‘Vn 2 E 2 ’) with 7,7,8,8-tetracyanoquinodimethane (TCNQ) are prepared and their structures determined. Spin concentration, mobilities and gap energies of the polycrystalline samples are evaluated from e.s.r. intensities and electrical conductivity measurements. The influence of the different chalcogen atoms on physical properties is discussed.

Synthesis and magnetic properties of transition metal cyclotetraphosphates M2P4O12 (M = Mn, Co, Ni, Cu)

Abstract Polycrystalline samples of isomorphous divalent metal cyclotetraphosphates M2P4O12 (M = Mn, Co, Ni, and Cu) were prepared and their magnetic properties investigated. The compounds were further analyzed by X-ray diffraction, ESR spectroscopy, and neutron diffraction. For the Mn, Co, and Ni compounds, below the Neel temperatures of TN = 3.2, 8.1, and 13.5 K, overall antiferromagnetic ordering was found. The susceptibility of Mn2P4O12 is interpreted in terms of a one-dimensional Heisenberg S = 5 2 model with antiferromagnetic nearest-neighbor interaction ( J k B = −1.0(1) K ). Cobalt and nickel cyclotetraphosphate do not exhibit quasi-one-dimensional magnetic behavior. Magnetization measurements revealed a spin-flop transition of Ni2P4O12 and a two-step metamagnetic phase transition for Co2P4O12. χ(T) diagrams of the cobalt compound indicate a strong anisotropy of susceptibility. No magnetic long-range order was observed by ESR and neutron diffraction in the case of Cu2P4O12 down to 1.7 K. ESR spectra showed exchange-narrowing at room temperature for the manganese compound and below 7.9 K for the copper compound.

Structure and dielectric relaxation of 2,3,7,8-tetramethoxychalcogenanthrene-TCNQ complexes

Abstract 2,3,7,8-Tetramethoxychalcogenanthrenes (5,10-dichalcogena- cyclo -diveratrylenes, Vn 2 EE′) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) form charge-transfer (CT) complexes of composition Vn 2 EE′·TCNQ (E = E′ = S, Se; E = S, E′ = Se, Te). The structure of the hitherto unknown compound Vn 2 STe·TCNQ is described. The dielectric relaxation of the whole series of CT complexes is determined and the results are correlated with the structural data.

Short- and medium-range order in amorphous rare-earth iron garnets

Abstract Amorphous rare-earth iron garnets, prepared by coprecipitation of hydroxides in ultrasonic fields, have been investigated to determine their short- and medium-range order. 57 Fe Mossbauer spectra reveal the magnetic transition temperature which is reduced to 14–25 K. From EXAFS data the coordination and the bond length of the ions are available.

Über das temperaturverhalten der 7Li-, 23Na- und der 133Cs-resonanz an den lithium-, natrium- und cäsiumformen des synthetischen zeoliths linde 13 X IM H2O- und D2O-gesättigten zustand

Abstract The dependence of the line-widths of the 7 Li, the 23 Na and the 133 Cs resonances on temperature has been studied on three samples of the synthetic zeolite Linde 13X containing different cations. The resonances have been measured at two frequencies in the H 2 O- and the D 2 O-saturated state. The results may be explained as follows: The cations and the adsorbed water form some kind of cation solution, freezing at low temperatures in the holes of the zeolite. In the frozen state the sodium and the cesium ions are situated on the walls of the holes binding one and two to three molecules of water respectively. For the lithium ions the experiments imply at the same conditions a hydration shell of four to five water molecules.

Relaxation methods for the study of ion transport in halide systems

Abstract Successful tools for the study of structural and dynamic problems in solid state ionic materials are electric and magnetic resonance and relaxation as well as the ITC (TSD) technique. Some applications of these structure-sensitive methods on fluoro-conducting systems in a wide range of temperature are demonstrated. The advantages, especially of the PMFG-NMR techniques, for a direct study of diffusion coefficients in these substances are shown. Correlations between local structures and ion conductivities are established.

Magnetic short-range order and spin freezing in the quasi-2D system LuFeMgO4

Abstract Neutron diffraction performed on the insulating compound LuFeMgO 4 revealed a gradual onset of anisotropic short-range ordering of the moments inside the random diluted double layers. Spin freezing which was observed by a saturation of the static correlations, Mossbauer hyperfine splitting and by a susceptibility maximum is ascribed to the competition between several antiferromagnetic interactions.

A magnetic and Mössbauer-spectroscopic study on the reduction of iron(II)-A-zeolites

Abstract Mossbauer spectra of the iron zeolites show that they are completely reduced. Above 25 K approximately 10% of the iron was found to be superparamagnetic with a mean particle size of 1.0 nm 3 . Approximately 90% of the iron remained paramagnetic with a decrease of the susceptibility from 1.5 × 10 -5 at 170 K to 3.5 × 10 -9 at 205 K.

Transport processes in fluoride crystals under high pressure

Abstract The effect of hydrostatic pressure on the ionic conductivities in β-PbF2 β-Pb1−x Mx mF2+(m−2)x (where Mm = Na+, Cd+2, Tb+3, U+4), LaF3 and La1−xCaxF3-x has been investigated in the temperature range between 300 K and 700 K for pressures up to 0.25 GPa (for β-PbF2) and 0.8 GPa (for LaF3). The activation volumes of defect formation and migration, impurity defect segregation and dissociation were determined from the effect of pressure on the conductivity. Keyes’ treatment based on the strain energy Zener model in Gruenisen approximation was used to estimate theoretical values of activation volumes.

SUBSTRATE EFFECT ON THE GROWTH OF IRON CLUSTERS IN Y ZEOLITE

Abstract Investigation of the decomposition process and of the thermolytic products obtained from Fe(CO) 5 /faujasite adducts by thermogravimetric, IR-spectroscopic, Mossbauer spectroscopic and X-ray absorption measurements (EXAFS) provides evidence for a substrate effect on the growth process of iron clusters. CsY substrate increases the FeCO bond strength. The stabilized intermediates generated by this effect upon thermolysis at 500 K are easily oxidized to small iron(III) oxide clusters, whereas with NaY substrate to a large extent iron(O) particles are generated. The latter show Mossbauer effect and EXAFS spectra comparable to those obtained from bulk iron. An inner oxidation process is assumed to be involved in the generation of the zeolite-supported iron oxide.