Synthesis, single crystal structure and lattice parameters

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The isostructural R2X2Z2O(BO3)3 borates (RCOB) crystallize in the acentric space group Cm. They are potential high-temperature piezoelectrics, which show an unknown structural instability. The present project focuses on the synthesis and Czochralski growth of RCOB (X, Z = Ca, R = La, Y, Gd, Pr, Nd, Er). As a second part structure and lattice parameters will be determined as a function of temperature. Based on the lattice parameters, an atomistic model of thermal expansion will be established. The qualitative evaluation of the crystals by determination of dislocation densities and point defects is planned. In addition, the chemical composition of RCOB should be expanded by variations in the cation positions, which are recently limited to Ca and rare-earth elements. The close collaboration with the project partners should provide information concerning the structure-property-relationships.