We present a thorough dielectric investigation of the hexagonal perovskites La 1.2 Sr 2.7 IrO 7.33 and La 1.2 Sr 2.7 RuO 7.33 in a broad frequency and temperature range, supplemented by additional infrared measurements. The occurrence of giant dielectric constants up to 10 5 is revealed to be due to electrode polarization. Aside of dc and ac conductivity contributions, we detect two intrinsic relaxation processes that can be ascribed to ionic hopping between different offcenter positions. In both materials we find evidence for charge transport via hopping of localized charge carriers. In the infrared region, three phonon bands are detected, followed by several electronic excitations. In addition, these materials provide further examples for the occurrence of a superlinear power law in the broadband ac conductivity, which recently was proposed to be a universal feature of all disordered matter.

Containing Peroxide Ions. -As revealed by powder X-ray and neutron diffraction the title compounds crystallize in the trigonal space group R3m with Z = 3. The structures contain isolated MO6 (M: Ru, Ir) octahedra, which are arranged in well-defined hexagonal perovskite slabs. These slabs are separated by [Sr2O1+δ] layers containing both O 2and ions. Compared to the Ru-compound, which shows Curie--Weiss behavior with an antiferromagnetic transition at 7 K, the magnetic susceptibility of the Ir compound is almost temperature-independent. -(GOETZFRIED*, T.; RELLER, A.; EBBINGHAUS, S. G.; Inorg.

Structure D 2000 Synthesis, Crystal Structure and Magnetic Properties of a New Ruthenium(V) Oxide: La1.2Sr2.7RuO7+δ. -The title compound is synthesized by solid state reaction of SrCO3, La2O3, and RuO2 (1250°C, 36 h). The samples are characterized by powder XRD, XANES, TGA, and magnetic measurements. La1.2Sr2.7RuO7+δ crystallizes in the trigonal space group R3m. The structure consists of uniform stacking of two AO3 layers and one A 2 O 1+δ layer (A: La/Sr). The A cations in the A 2 O 1+δ layer are trigonal-prismatically coordinated and the Ru ions occupy the octahedral sites between the AO3 layers. -(GOETZFRIED*, T.; RELLER, A.; EBBINGHAUS, S. G.; Solid State Sci. 6