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The structures of the new compound La(1.2)Sr(2.7)IrO(7.33) and the recently discovered La(1.2)Sr(2.7)RuO(7.33) have been solved using a combination of X-ray and neutron diffraction. Both compounds crystallize in the trigonal space group Rm and consist of isolated MO6 (M = Ru, Ir) octahedra, which are arranged in well-defined hexagonal perovskite slabs. These slabs are separated by (Sr2O(1+delta)) layers containing both O2- and (O2)2- ions. The composition can therefore be written as La(1.2)Sr(2.7)MO(7-delta)(O2)delta with delta = 0.33. Results of the magnetic susceptibility and XANES measurements show that the transition metal cations are in a pentavalent state. While in La(1.2)Sr(2.7)RuO(7.33) an antiferromagnetic interaction between the Ru5+ ions is found, La(1.2)Sr(2.7)IrO(7.33) shows a very small temperature-independent paramagnetism down to 1.8 K due to the strong spin-orbit coupling characteristic for the 5d element iridium.

The origin of spin-dimerization and concomitant spin-gap opening in the triclinic phase of poly-and single-crystalline La 2 RuO 5 at unusually high temperatures was investigated using magnetic susceptibility and specific-heat measurements. From the low-temperature crystal structure the formation of antiferromagnetically coupled Ru 4+ (S = 1) dimers within the quasi-two-dimensional magnetic system can be deduced, resulting in a nonmagnetic singlet state. It was found that the antiferromagnetic coupling within the dimers is much stronger than the interaction with neighboring dimers. La 2 RuO 5 exhibits a step-like change in the magnetic susceptibility at 161 K, indicating a first-order transition of combined magnetic and structural character. The size of the spin-gap has been estimated from the thermally activated behavior in the low-temperature dimerized phase and was found to be significantly different in the polycrystalline sample when compared to the results obtained from the single crystals. The magnetic entropy obtained from specific-heat measurements amounts to roughly 0.5R ln(3), reflecting solely the contribution of spin degrees of freedom to the entropy change during the phase transition.

Simultaneous thermogravimetry and thermomicroscopy were performed on Ca-oxalates which play an important role in the appearance of oxalate films connected with lichens superficially growing on human artefacts. Ca-oxalate exists in two well-described modifications: as the more stable monoclinic monohydrate whewellite and the less stable tetragonal dihydrate weddelite. Weddelite serves for lichens as a water absorbing and accumulating substrate which transforms to wheweUite when humidity drops. To follow these morphological changes optically and the water loss gravimetrically at the same time, a combination of thermomicroscopy and thermogravimetric analysis was constructed. The reflection light microscope was connected to a video camera and computer so that the morphological changes and the thermogravimetric curves could be shown simultaneously on the screen as function of time and temperature.Lichens -double organisms composed of algae and fungi -form surface layers not only on natural organic and inorganic material but also on human artefacts. In calcareous artefacts such as the famous Chinese terracotta soldiers or Egyptian epigraphs they lead to a destruction of the surface by forming Ca-oxalate layers and thus to a deterioration of the historian work of art. But in places where the surface is covered by some blue colours (Egyptian and Chinese Blue, Chinese Purple) the growth of lichens is inhibited and the artefacts are well preserved. The copper ion contained in the pigments is responsible for this effect since copper is a strong poison for microorganism.As lichens exhibit an extremely slow growth under natural and laboratory conditions the two lichen components: algae and fungi were investigated separately. The three mentioned ancient pigments have very low solubility products and thus do not act on the quickly growing fungi. But under special experimental conditions Egyptian Blue formed clear halos on the growth plates of the algae Chlorella minutissima and Trebouxia glomerata. These halos were compared with those of the easily soluble copper sulphate as a standard.