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Polarized second-order Raman scattering spectra of CuO single crystals are reported. It is shown that for some scattering geometries the second-order processes dominate the inelastic light scattering spectra. Group-theoretical symmetry analysis of the selection rules for the first- and second-order scattering processes is performed and phonon dispersion relations are calculated within density functional theory. The main spectral features of the two-phonon spectra are assigned to overtones of the vibrational branches at various special points across the Brillouin zone.

Copper-divanadate Cu2−yZnyV2O7 comprises trans-edge sharing chains of CuO5 polyhedra where Cu spins S= 1 2 are antiferromagnetically coupled. Zn substitution for Cu induces a structural phase transition which affects strongly the magnetic properties. In particular, a substantial magnetic anisotropy found in one of the structural phases is strongly suppressed in the other one, owing to the changes of the local bonding geometry.

Cs4K2CuSi2O8: Synthesis, Crystal Structure, UV-Vis-IR Data Cs4K2CuSi2O8 may be obtained via a redox reaction of KCuO2 in the presence of Cs2O and SiO2 with the container material (Cu) at 450 °C as blue single crystals which are sensitive to moisture. Powder samples were obtained by annealing intimate mixtures of the binary oxides under an inert gas atmosphere (Ar) in sealed Ag containers at 500 °C. The crystal structure contains isolated trimeric anions of [O2SiO2CuO2SiO2]6–. Cu2+ in square-planar coordination share trans-edges with [SiO4] tetrahedra. Spectroscopic investigations focus on the bonding situation of the [CuO4] unit (AOM) and characteristic vibrational modes of the silicate.

Measurements of magnetization, electrical resistivity and nuclear- and electron spin resonance in In2VO5 reveal a remarkable interplay of different degrees of freedom in the zigzag V-0 chains (V4+, 3d1, S = 1/2) which are realized in this material. At high temperatures the d electrons are itinerant and magnetic interactions are ferromagnetic. Below a crossover temperature T* ~120 K the d states get localized and interact predominantly antiferromagnetically. Though magnetic resonance data clearly indicate the slowing down of the spin-spin correlations by approaching a characteristic temperature Tsro ~ 20 K the system does not long-range order magnetically. We attribute these peculiar crossover phenomena to the unusual anisotropic thermal contraction of the lattice which controls the localization of the d-states, magnetic exchange and frustration.

In the crystal structure of [NdCl(NO3)2(tetraglyme)] (triclinic, P1, Z = 2, a = 7.814(1); b = 7.9832(9); c = 15.322(2) A; α = 87.38(1); β = 84.88(1); γ = 79.83(1)°), neodymium is ten coordinate with two transoid chelating nitrate ligands, a chlorine and the five oxygen atoms of the tetraglyme ligand in an irregular array.

Crystal Structure and Absorptionspectrum of Cs4CuSi2O7, EPR Spectra of K6CuSi2O8 and A4CuSi2O7 (A = Rb, Cs), a Comparison with Egyptian Blue, CaCuSi4O10 Cs4CuSi2O7 is obtained by annealing intimate mixtures of Cs2O, CuO and SiO2 in sealed Ag containers at 500 °C as a greenish-blue powder which is sensitive to moisture. The crystal structure (triclinic, P1) contains chains of [CuSi2O7] with Cu2+ in square-planar coordination. The absorption and EPR spectra of Cs4CuSi2O7, K6CuSi2O8 and Rb4CuSi2O7 are discussed in terms of the Angular-Overlap-Model (AOM) and compared with Egyptian blue, CaCuSi4O10.

The orbital excitations of a series of transition-metal compounds are studied by means of optical spectroscopy. Our aim was to identify signatures of collective orbital excitations by comparison with experimental and theoretical results for predominantly local crystal-field excitations. To this end, we have studied TiOCl, RTiO3 (R=La, Sm, Y), LaMnO3, Y2BaNiO5, CaCu2O3, and K4Cu4OCl10, ranging from early to late transition-metal ions, from t_2g to e_g systems, and including systems in which the exchange coupling is predominantly three-dimensional, one-dimensional or zero-dimensional. With the exception of LaMnO3, we find orbital excitations in all compounds. We discuss the competition between orbital fluctuations (for dominant exchange coupling) and crystal-field splitting (for dominant coupling to the lattice). Comparison of our experimental results with configuration-interaction cluster calculations in general yield good agreement, demonstrating that the coupling to the lattice is important for a quantitative description of the orbital excitations in these compounds. However, detailed theoretical predictions for the contribution of collective orbital modes to the optical conductivity (e.g., the line shape or the polarization dependence) are required to decide on a possible contribution of orbital fluctuations at low energies, in particular in case of the orbital excitations at about 0.25 eV in RTiO3. Further calculations are called for which take into account the exchange interactions between the orbitals and the coupling to the lattice on an equal footing., published version, discussion of TiOCl extended to low T, improved calculation of orbital excitation energies in TiOCl, figure 16 improved, references updated, 33 pages, 20 figures

Na10[CoO3]{[CoO3](OH)2} wurde durch Redoxreaktion zwischen metallischem Cobalt und CdO in Anwesenheit von NaOH und Na2O bei 600 °C (21 d) in Form roter Einkristalle erhalten. Die Kristallstruktur wurde anhand von Einkristalldaten bestimmt (IPDS-Daten, Pnma, Z = 4, a = 988, 5(1) pm, b = 1013, 9(2) pm, c = 1186, 3(2) pm, wR2 = 0, 079). Weiterhin werden schwingungsspektroskopische Ergebnisse und Betrachtungen zum Madelung-Anteil der Gitterenergie prasentiert. A Sodium-Oxocobaltate(II)-Hydroxide: Na5[CoO3]OH ≡ Na10[CoO3]{[CoO3](OH)2} Na10[CoO3]{[CoO3](OH)2} has been obtained from a redox reaction between cobalt metal and CdO in the presence of NaOH and Na2O at 600 °C (21 d) as red single crystals. The structure has been determined from single crystal data (IPDS-data, Pnma, Z = 4, a = 988.5(1) pm, b = 1013.9(2) pm, c = 1186.3(2) pm, wR2 = 0.079). Furthermore IR data and aspects of the Madelung part of the lattice energy are presented.

Na9[FeO3][FeO4]a Mixed Valent Oxoferrat(II, III) with Isolated [FeO3]4— — and [FeO4]5— Anions Na9[FeO3][FeO4] has been formed and obtained from a redox reaction between CdO and iron metal (reaction container) and Na2O in the presence of NaOH at 450 °C as orange-red transparent single crystals. The crystal structure determination (IPDS data: Pca21, a = 956.2(2) pm, b = 999.1(2) pm, c = 1032.3(2) pm, Z = 4, Rall = 0.0455) reveals the presence of isolated complex anions, [FeO3]4— and [FeO4]5—.

K3[Fe2O4] wurde erstmals beim Tempern von „Cs3K3CdO4” in verschlossenen Fe-Zylindern (36 d bei 450–480 °C) in Form dunkelroter, transparenter Einkristalle erhalten. Die Strukturaufklarung (IPDS-Diffraktometerdaten, MoKα, vermessene Reflexe: 1891, davon 234 symmetrieunabhangig, R1 = 0,033, wR2 = 0,088) belegt die Raumgruppe Fddd; a = 596,11(9), b = 1140,3(1) c = 1717,9(3) pm; Z = 8. In der Struktur, die als eine aufgefullte Variante des KFeO2-Typs aufgefast werden kann, liegen dreidimensional uber Ecken verknupfte tetraedrische [FeO4]-Einheiten vor. K2[Fe2O4] wurde durch Oxidation von metallischem Eisen mit KO2 in Gegenwart von Na2O in Form schwarzer Einkristalle erhalten (520 °C) und kristallisiert in der Raumgruppe Pbca (a = 559,18(7), b = 1122,1(1), c = 1592,8(2) pm; Z = 8; IPDS-Diffraktometerdaten, MoKα, vermessene Reflexe: 9543, davon 1213 symmetrieunabhangig, R1 = 0,043, wR2 = 0,102). The Mixed-Valent Oxoferrate(II,III) K3[Fe2O4] – A Stuffed Variant of the K2[Fe2O4] Type of Structure K3[Fe2O4] has been obtained by tempering “Cs3K3CdO4” in sealed Fe containers (36 d at 450–480 °C) as dark red transparent single crystals of rectangular shape. The structure determination (IPDS diffractometer data, MoKα, 1891 collected reflections, 234 symmetry independent, R1 = 0.033, wR2 = 0.088) confirms the space group Fddd; a = 596.11(9), b = 1140.3(1), c = 1717.9(3) pm; Z = 8. K3[Fe2O4] exhibits a structure with [FeO4] tetrahedra connected via corners leading to a three-dimensional network closely related to the KFeO2 type of structure. From the oxidation at 520 °C of iron metal with KO2 in the presence of Na2O black single crystal of K2[Fe2O4] have been obtained. K2[Fe2O4] crystallizes in the space group Pbca with Z = 8 and a = 559.18(7), b = 1122.1(1), c = 1592.8(2) pm (IPDS diffractometer data, MoKα, collected refelctions: 9543, 1213 symmetry independent, R1 = 0.043, wR2 = 0.102).