Ferroelectricity in K0.992Rb0.008Ta0.96Nb0.04O3

Abstract Abstract We report on the first crystal growth and Raman scattering studies in K0.992Rb0.008Ta0.96Nb0.04O3 (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-niobateRaman scatteringferroelectricityphase transitionPACS: 77.84.Dy78.30.Hv77.80−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.