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Polarized far-infrared reflectivity and Raman scattering spectra of LiNaGe 4 O 9 single crystals were studied between 15 and 300 K. Even if the ferroelectric phase transition in this material is of order-disorder type and critical relaxation was estimated from our data in the region 0.13 to 13 cm -1 , pronounced phonon softening in four different symmetry spectra was observed near T c . This indicates changes in interatomic bonds caused by local Li and Na atom ordering and accompanying shifts of GeO polyhedra even above T c . Phonon anomalies observed about 45 K below T c in the E ∥ a far-infrared spectra might suggest another phase transition, but no corresponding dielectric anomaly was observed in previous dielectric measurements.

Room-temperature infrared (IR) reflectivity, terahertz transmission and evaluated effective complex dielectric response of four polycrystalline alumina ceramics (corundum) with highly anisotropic grains in the IR range were determined. The spectra were compared with modelled spectra based on the known IR response of sapphire single crystal and Bruggeman and Lichtenecker models of the effective medium approximation (EMA). The results are extremely sensitive to the surface treatment (polishing), but do not depend on the grain size in the range of ∼0.3–1 μm and on the weak doping, needed for processing of optically transparent ceramics. As all the samples show similar grain shapes and topology, no measurable differences among the fully dense samples were observed. Agreement with the modelled spectra is reasonable, but shows a higher effective mode damping. A weak geometrical resonance was revealed near 500 cm−1, better described by the Bruggeman model. The small sample porosity up to 6.2% is revealed mainly as a reduced reflectivity above ∼650 cm−1, which produces weak losses in the high-frequency range above the TO phonon modes, better described by the Lichtenecker model.

Fourteen new structural phase transitions are detected in layer-type monoalkylammonium hexachloro-stannates (CnH2n+1NH3)2SnCl6 (n = 2 to 8) by means of differential scanning calorimetry. The basic thermodynamic data are determined for the transitions. The infrared spectra of the compounds are measured in the range of molecular vibrations (500 to 4000 cm−1) at room temperature and in dependence on temperature (77 to 298 K) by the method of nujol mull. Vierzehn neue strukturelle Phasenumwandlungen werden in geschichteten Monoalkylammonium-hexachlorostannaten (CnH2n+1NH3)2SnCl6 (n = 2 bis 8) mittels dynamischer Leistungs-Differenzkalorimetrie entdeckt. Es werden die thermodynamischen Grunddaten fur diese Umwandlungen ermittelt. Die Infrarotspektren dieser Verbindungen werden im Bereich der Molekulschwingungen (500 bis 4000 cm−1) bei Raumtemperatur und in Abhangigkeit von der Temperatur (77 bis 298 K.) mit Hilfe einer Nujolsuspension gemessen.

Raman spectra of Rb2CoCl4 (RCC) single crystals, prepared by an improved method, are studied at 90 to 297 K. The results show that the temperature dependence of the spectra of RCC is analogous to that of Rb2ZnCl4 and Rb2ZnBr4. Eigenfrequencies of internal modes v1 and v3 vary with temperature in a manner well describable by a model, which is suggested by Rasing et al. for Rb2ZnBr4. Low-frequency lines at 20 and 37 cm−1 exhibit a pronounced temperature dependence. The broadness of spectral lines speaks for a high anharmonicity of oscillations in RCC. Zwischen 90 bis 297 K werden die Ramanspektren von Rb2CoCl4 (RCC)-Einkristallen, hergestellt nach einer verbesserten Methode, untersucht. Die Ergebnisse zeigen, das die Temperaturabhangigkeit von RCC zu dem von Rb2ZnCl4 und Rb2ZnBr4 analog ist. Die Eigenfrequenzen der inneren Moden v1 und v3 variieren mit der Temperatur in einer Weise, die gut durch ein von Rasing et al. fur Rb2ZnBr4 vorgeschlagenes Modell erklart werden kann. Die Niederfrequenzlinien bei 20 und 37 cm−1 zeigen eine ausgepragte Temperaturabhangigkeit. Die grose Breite der Spektrallinien weist auf eine hohe Anharmonizitat der Oszillationen in RCC hin.