I.G. Krogh Andersen

The crystal structure of lanthanum manganate(iii), LaMnO3, at room temperature and at 1273 K under N2

Abstract Orthorhombic stoichiometric LaMnO 3 is prepared by heating rhombohedral LaMaO 3+δ under N 2 at 1173 K and cooling to room temperature under N 2 . The thermal transformations of orthorhombic lanthanum manganate(III) were investigated using high-temperature X-ray powder diffraction. Transformations orthorhombic—cubic—rhombohedral were observed. The dependence of the unit cell parameters on temperature was determined. The crystal structures of LaMnO 3 at room temperature (orthorhombic) and at high temperature (rhombohedral at 1273 K in N 2 ) were determined using neutron powder diffraction.

Neutron diffraction determination of full structures of anhydrous LiX and LiY zeolites

Abstract Virtually monoionic LiX and LiY zeolites have been prepared by LiOH titration of parent NH 4 zeolites. Structural studies have been performed at room temperature on the anhydrous zeolites, Li 80.7 H 4.9 Na 0.4 Al 86 Si 106 O 384 and Li 46.0 H 5.8 Na 5.1 K 0.1 Al 57 Si 135 O 384 , by powder neutron diffraction profile refinement in order to locate Li + cations. The cell parameters are 24.6716(10) and 24.4498(12) A for LiX and LiY, respectively. Three positions have been found for Li + , sites I′ and II in the six-ring windows of the sodalite unit and site III′ in the supercage for the additional Li + of LiX.

Tin-mordenites, syntheses and ionic conductivity

Abstract Tin-mordenites were prepared by heating H-mordenite mixed with tin (II) chloride dihydrate in an oxygen atmosphere. Tin was ion exchanged into the mordenites with up to 3.6 molecules per unit cell. Excess tin (II) chloride was oxidized to tin (IV) oxide by oxygen. The ac and dc conductivities were measured in atmospheres with different water partial pressures. The conductivity measurements showed that the tin exchanged mordenites were proton conductors, that the conductivity was very dependent of the water content, but that the dehydration was reversible. The conductivity increased with increasing tin content until full ion exchange whereafter it remained virtually constant. Tin (IV) oxide in the preparates gave rise to additional grain boundary conduction. The highest conductivity measured was σ=0.6×10-1(ωcm)-1 at 120°C in a water saturated atmosphere.

Proton conduction in H2Ti4O9, 1.2 H2O

Abstract H 2 Ti 4 O 9 , x H 2 O was prepared from K 2 Ti 4 O 9 by hydrolysis with 0.4 M nitric acid as described by Marchand and co-workers. The K 2 Ti 4 O 9 was prepared by a conventional solid state reaction, and by a sol/gel procedure. The ac conductivity was measured conventionally, and also under a load of 0.5 V. The temperature range was from 20–100°C. The measuring cell was purged with gas (N 2 or H 2 ) saturated with water vapor at the measuring temperature. Carbon electrodes were used. The dc conductivity was measured on tablets with platinum black electrodes in an atmosphere of hydrogen saturated with water vapour at 75% RH. The maximum conductivity was 1.8 × 10 −3 (Ω cm) −1 .

α-zirconium hydrogenphosphate, monohydrate. preparation, chemical properties and ac conductivity

Abstract The preparation of zirconium hydrogenphosphate, monohydrate (αZrP) was performed by two methods giving materials with slightly different properties. It is shown that the particle size of αZrP depend upon the method of preparation and the washing procedures, and that the ac conductivity decreases with increasing particle size (5 x 10 -6 to 5 x 10 -5 Ω -1 cm -1 at 20°C). The activation energy has been determined to 0.25 eV/mol (between 20°C and about 100°C) independent of the particle size, showing αZrP to be a surface ion conductor.

Synthesis and structure of lithium cesium and lithium thallium cancrinites

X-ray powder diffraction studies of synthetic cancrinites were undertaken to elucidate the role of lithium ions and large cations (Cs, Tl) in zeolite crystallizations. Li 4.56 Cs 1.50 Al 6 Si 6 O 24 , 4.9 H 2 O (a = b = 12.4328 (12) A, c = 4.9692 (6) A, hexagonal, P6 3 , Z = 1). The structure was refined by the Rietveld diffraction-profile refinement technique. The cesium ions — located in the cancrinite cage only — are coordinated to 12 oxygen atoms (at distances 3.15–3.61 A). In accordance with their position, they are not exchangeable. The lithium ions are four coordinated to oxygen atoms (at distances 1.91 to 2.03 A). Li 2.75 Tl 3.23 Al 5.85 Si 6.13 O 24 , 2.0 H 2 O (a = b = 12.4419 (7) A, c = 4.9884 (4) A, hexagonal, P6 3 , Z = 1. The thallium ions are located on more than one position in the cancrinite cage, and there is also thallium on one position in the channels. This is in accordance with the thallium ions being partially exchangeable in this material. The structures are described and the action of small and large ion radius cations in cancrinite crystallization is discussed.

Study of preparation and ac/dc conductivity of tin-zeolite-Y materials

Abstract Tin-zeolite-Y materials were prepared by heating zeolite H-Y mixed with tin (II) chloride dihydrate. Excess of tin (II) was oxidized to tin (IV) oxide by oxygen. The ac and dc conductivities were measured in atmospheres of constant relative humidity in the temperature range 25°C to 116°C. The materials are protonic conductors. The highest measured conductivity was 0.9×10 -3 (Ω cm) -1 .

Tin-zeolites, syntheses and ionic conductivity

Abstract By preparation of tin-ferrierites, tin-silicalites, tin-mordenites and tin-zeolite-Ys it has been shown that the treatment of H-zeolites with tin (II) chloride dihydrate is a general method for preparing tin-zeolites. In the syntheses a part of the tin is ion-exchanged with protons in the H-zeolite and excess tin (II) chloride is converted in an oxygen atmosphere to tin (IV) oxide and tin(IV) chloride. Syntheses of the tin-zeolites on a thermobalance confirm the results. X-ray analyses show a small change in the b-axis for tin-mordenites and a transition from monoclinic to orthorhombic for the tin-silicalites. The highest ac bulk conductivity at 100% relative humidity is in the range from 10−2 (Ω cm)−1 for tin-mordenites to 10−3 (Ω cm)−1 for the other tin-zeolite s. All tin-zeolites are proton conductors.

Tin(IV) oxide containing mordenite; Syntheses and ionic conductivity measurements

Mordenites containing tin(IV) oxide were prepared by heating the mordenites with tin(IV) sulfate or tin(II) chloride dihydrate. The conductivities were measured in atmospheres with different water partial pressures. The conductivities of the tin(IV) oxide containing mordenites were higher than the conductivity of the pure mordenite. The highest conductivity was 2.5×10 −2 (Ω cm) −1 measured at 100°C and in an atmosphere with a relative humidity of 100%.

The ionic conductivity of alkalimetal-zeolite X

Zeolite X is an aluminosilicate. We have investigated a series of Na, Li-X zeolites with lithium contents between 0 and 96 mole%. They were prepared by exchange of Na-X in lithium chloride solutions at 100°C. The samples were carefully washed. After vacuum drying at 250°C, pellets were pressed and gold electrodes were evaporated on to them. The ac conductivity was measured in the frequency range from 65 kHz to 4 Hz. The conductivities were measured in the temperature range from room temperature to ≈300°C. Substitution of even a small amount of sodium with lithium decreases the conductivity significantly and increases the activation energy. de conductivity measurements with lithium electrodes of the most lithium rich samples have shown that they are lithium ion conductors. The logarithm of the preexponential factor plotted against the activation energy is linear. The slope of this line indicates that all the Arrhenius plots intersect at ≈360°C. Above this temperature the lithium-containing zeolites will have higher conductivity than the sodium form. Potassium and cesium containing zeolite X was prepared (the Cs-X sample contained 58 mole% Cs) and measured in the same way as the lithium form. AT 150°C the specific conductivities were in the range from 5×10 −10 for the cesium form to 3×10 −6 (ω cm) −1 for the sodium form. Na-X has the highest conductivity at temperatures below 360°C.