Structure analysis of alkaline earth tellurates (IV)

Tellurates(IV) contain a non-bonded electron pair E which frequently is stereochemically active and induces an asymmetric environment in the crystal structure. Thus some of these compounds crystallize in one of the non- centrosymmetric space groups which is a precondition for ferroelectric or nonlinear optical (NLO) properties of respective materials. Indeed, two alkaline earth tellurates(IV), viz. CaTeO 3 and SrTe0 3 , exhibit ferroelectric behaviour. As a basic requirement for understanding and interpretation of ferroelectric properties of these materials, the knowledge of the underlying crystal structures and phase transition points is essential. The compounds of general formula MTeO3 (M = Ca, Sr and Ba) likewise show polymorphism, but only for two BaTeO 3 modifications the crystal structures are satisfactorily determined. For SrTe0 3 two polymorphs with apparently erroneous crystal structures are reported, and for three polymorphs of CaTeO 3 likewise dubious X-ray powder data are given. The present project aims at the preparation of single-phase material, and the characterisation, crystallography, thermal behaviour and electric properties of MTeO3 phases and solid solutions of the series M 1-x M` x TeO 3 (M, M` = Ca, Sr, Ba). One main focus is intended on the single crystal growth of respective phases utilizing various methods like flux techniques, hydrothermal treatment and chemical transport reactions. X-ray powder diffraction and high-resolution electron microscopy will supplement this analytical tool. Another main emphasis pertains to the thermal behaviour of MTeO3 phases with complementary in-situ techniques (DTA, DSC; temperature-dependent X-ray diffraction) which will allow identifying solid state reactions and phase transition points between ferroelectric and paraelectric phases. Further characterisation will make use of chemical-analytical, and spectroscopic methods. Measurement of the electric properties of ferroelectric MTeO3 phases and in particular of solid solutions M 1- x M` x TeO 3 will complete the project. The proposed research project will help to get a deeper insight into the structure-property relations of ferroelectric alkaline earth tellurates(IV) and their corresponding solid solutions.

Tellurates(IV) contain a non-bonded electron pair E which frequently is stereochemically active and induces an asymmetric environment in the crystal structure. Thus some of these compounds crystallize in one of the non- centrosymmetric space groups which is a precondition for ferroelectric or nonlinear optical (NLO) properties of respective materials. Indeed, two alkaline earth tellurates(IV), viz. CaTeO 3 and SrTe0 3 , exhibit ferroelectric behaviour. As a basic requirement for understanding and interpretation of ferroelectric properties of these materials, the knowledge of the underlying crystal structures and phase transition points is essential. The compounds of general formula MTeO 3 (M = Ca, Sr and Ba) likewise show polymorphism, but only for two BaTeO 3 modifications the crystal structures are satisfactorily determined. For SrTe0 3 two polymorphs with apparently erroneous crystal structures are reported, and for three polymorphs of CaTeO 3 likewise dubious X-ray powder data are given. The present project aims at the preparation of single-phase material, and the characterisation, crystallography, thermal behaviour and electric properties of MTeO3 phases and solid solutions of the series M 1-xM`x TeO 3 (M, M` = Ca, Sr, Ba). One main focus is intended on the single crystal growth of respective phases utilizing various methods like flux techniques, hydrothermal treatment and chemical transport reactions. X-ray powder diffraction and high-resolution electron microscopy will supplement this analytical tool. Another main emphasis pertains to the thermal behaviour of MTeO 3 phases with complementary in-situ techniques (DTA, DSC; temperature-dependent X-ray diffraction) which will allow identifying solid state reactions and phase transition points between ferroelectric and paraelectric phases. Further characterisation will make use of chemical-analytical, and spectroscopic methods. Measurement of the electric properties of ferroelectric MTeO 3 phases and in particular of solid solutions M 1- xM`x TeO 3 will complete the project. The proposed research project will help to get a deeper insight into the structure-property relations of ferroelectric alkaline earth tellurates(IV) and their corresponding solid solutions.