Tantalum borate (TaBO,) has the zircon structure with unusual Coordination for the cations: Ta5+ in eight-and B3+ in four-coordination. The infrared and Raman spectrum is reported and discussed. The symmetrical and asymmetrical B0:valence stretching lics a t much lower energy than usually observed in borates. A comparison with other compounds with zircon structure is made. TaBO, shows a bluish-white luminescence under ultraviolet excitation at temperatures below liquid N, temperature. The emission consists of at least two snbbands. A comparison with YTaO, is made. Tantalborat (TaBO,) ist rnit Zirkon isotyp. Es liegt jedoch eine nicht iibliche Boordinationszahl fur die Kationen vor : Tast hat die Koordinationszahl acht und Bs+ vier. Die IRund Raman-Spektren dieses Borats werden mitgeteilt und diskutiert. Die symmetrische und asymmetrische BOi--Valenzschwingung liegt bei niedrigerer Energie als iiblich in Boratverbindungen. Diese Spektren werden mit Literaturangaben f iir andere Verbindungen mit Zirkonstruktur verglichen. TaBO, zeigt eine blaulich-weiBe Emission unter Anregring mit ultravioletter Strahlung bei Teniperaturen unterhalb des fltissigen Stickstoffs. Diese Lumineszenz enthalt mindestens zwei Subbanden. Ein Vergleich mit der Lumineszenz von Yttrinnitantalat wird diskutiert.
The Raman and infrared spectra of compounds NaLnTi04 (Ln = lanthanide, including yttrium) are reported and discussed. Their most striking feature is a strong band in both spectra at about 900 cm-'. This band is ascribed to a vibration localized in the Ti-0 bond directed towards the Na-0 layers. The relevant oxygen anion is very poorly charge compensated, and the X-0 bond is, therefore, very strong. Pauling's electrostatic valence rule appears to be of great use in these considerations. These compounds do not show ferroelectricity.
The infrared, Raman and luminescence spectra of cubic Na3NbO4 are reported. From this we conclude that the structure is that of rocksalt with a more or less disordered distribution of the N~ and Nb s+ ions among the cation sites.
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