Abstract
The magnetic and electrical properties of some TTB type niobates and tantalates of Eu II with general formula Eu x NbO 3 (0.5⩽ x⩽ 0.6), Eu 0.5TaO 3 and EuBCM 5O 15 (M = Ta, Nb; B = Eu II, Sr, Ba; C = Na, K) have been investigated. Suceptibility measurements showed a large proportion of Eu 3+ ions among the Eu 2+ ions, and this was confirmed by Mössbauer spectroscopy. Mössbauer spectra also showed the absence of any magnetic ordering of the europium ions down to 4.2K, and the absence of any charge hopping phenomena up to room temperature. Conductivity and Seebeck coefficient measurements revealed typical semiconductor behaviour from 77 to 800 K. The Seebeck coefficient vs temperature curves showed a hopping conductivity regime at low temperature and an extrinsic semiconductor conductivity at high temperature. A Goodenough type of derived schematic energy level model for the tungsten bronze type structure was found to be qualitatively in agreement with the experimental results.
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