Synthesis and Crystal Chemistry of New Transition Metal Tellurium Oxides in Compounds Containing Lead and Barium
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Synthesis and Crystal Chemistry of New Transition Metal Tellurium Oxides in Compounds Containing Lead and Barium Boris Wedel, DOWA Mining Company Ltd., Central Research Laboratory, Hachioji, Japan, Katsumasa Sugiyama, Kimio Itagaki, Tohoku University, Institute for Advanced Materials Processing, Sendai Japan. Hanskarl Müller-Buschbaum, Christian Albrechts University, Institute for Inorganic Chemistry, Kiel, Germany. ABSTRACT During the past decades the solid state chemistry of tellurium oxides has been enriched by a series of quaternary metallates. Interest attaches not only to the chemical and physical properties of these compounds, but also to their structure, which have been studied by modern methods. The partial similarity of earth alkaline metals and lead in solid state chemistry and their relationships in oxides opens a wide field of investigations. Eight new compounds in the systems Ba-M-Te-O (M= Nb, Ta) and Pb-M-Te-O (M = Mn, Ni, Cu, Zn) were prepared and structurally characterized: Ba2Nb2TeO10, Ba2M6Te2O21 (M = Nb, Ta) and the lead compounds PbMnTeO3, Pb3Ni4.5Te2.5O15, PbCu3TeO7, PbZn4SiTeO10 and the mixed compound PbMn2Ni6Te3O18. The structures of all compounds are based on frameworks of edge and corner sharing oxygen octahedra of the transition metal and the tellurium. Various different channel structures were observed and distinguished. The compounds were prepared by heating from mixtures of the oxides, and the single crystals were grown by flux method or solid state reactions on air. The synthesis conditions were modified to obtained microcrystalline material for purification and structural characterizations, which were carried out using a variety of tools including powder diffraction data and refinements of X-ray data. Relationships between lead transition metal tellurium oxides and the earth alkaline transition metals tellurium oxides are compared. INTRODUCTION So-called ‘lone pair’ cations such as Pb2+ or Te4+, contain two valence electrons in their outer occupied s2-orbital. This s2-orbital can be stereoactiv. The influence of the stereoactiv s2orbital becomes obvious by a distortion the local coordination environment. In crystal chemistry, the lone pair can be treated as a ligand of the cation. The shift of the lone pair cation out of the center of its coordination polyhedron results in an asymmetric coordination environment, which can lead to a variety of interesting physical properties. The tellurium oxide compounds are more and more attractive to the researcher, because of the interesting structural chemistry of Te(IV) and as alternative material for tungsten or 4th an 5th group transition metals as solid state device materials. Quaternary earth alkaline tellurium oxides with 4th period transition elements crystallize in numerous variants of the perovskite type. The earth alkaline metal can be substituted by lead in these systems and the perovskite structure is retained. Pure lead quaternary 4th period transition elements tellurium oxides were hitherto unknown. Our study includes high temperatur
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