Crystal Growth and Dielectric Study of the Niobate Series K3Sr2RNb10O30 (R = Lanthanide) of Tungsten Bronze Structure

Abstract

Fibre single crystals of K3Sr2RNb10O30 (R = La, Nd, Eu, Gd, Sm) have been successfully grown using the μ-pulling down method. Single crystal X-ray diffraction technique has confirmed that all isolated compounds crystallize with the tetragonal tungsten bronze structure. The elemental analyses of Nd- and Eucrystals using EDX has evidenced the presence of some inclusions corresponding to the composition KNb3O8. The presence of such compound in the matrix of the grown fibres could be interpreted as a revelation of the quaternary equilibrium involved during the crystal growth. Dielectric and Raman investigations within a wide temperature range [–150 °C; 400 °C], tend to confirm the existence of the same thermal anomalies. Although these anomalies are found at almost the same temperatures, the nature and the mechanisms of the so-revealed phase transitions are not yet totally evidenced.