Ferroelectricity in K_0.992Rb_0.008Ta_0.96Nb_0.04O₃

Abstract

We report on the first crystal growth and Raman scattering studies in K_0.992Rb_0.008Ta_0.96Nb_0.04O₃ (KRTN) and KTaO₃:Rb (3% mol. in the melt), in which Rb⁺ ions (ionic radius 1.47 Åt) substitute K⁺(1.33 Åt). The experiments were performed in the range 10–300 K and focused on the behavior of TO₁ and TO₄ modes. The results confirm indications by previous dielectric permittivity data about the ferroelectric nature of the phase transition in KRTN. It appears that a small amount of Rb changes the character of the phase transition induced by Nb from mainly displacive to mainly order-disorder, whereas no evidence of ferroelectricity is revealed in the KTaO₃:Rb sample.

Keywords:

• Potassium-rubidium tantalate-niobate
• Raman scattering
• ferroelectricity
• phase transition

PACS:

• 77.84.Dy
• 78.30.Hv
• 77.80−e

Acknowledgments

This work has been supported by Grant FIRB RBNE01KZ9 from the Italian Ministry of Education. We are grateful to Dr. R. Oberti for compositional analysis in KRTN.