Critical Point of Relaxor K_1−xLi_xTaO₃ Under an Electric Field

Abstract

Optical second harmonic (SH) intensities and dielectric constants of Li doped KTaO ₃ are measured under an external electric field. Applying the Landau-Devonshire phenomenological theory to the temperature dependence of SH intensities, we find that the order of ferroelectric phase transition changes from 2nd to 1st with the increase of Li concentration. The dielectric measurement reveals that a critical behaviour similar to Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ is observed. Additionally, we find that the critical electric field depends on the frequency of electric field and the effect becomes conspicuous in lower frequencies in Li doped KTaO ₃ .

Keywords:

• Quantum paraelectrics
• relaxor
• critical behaviour
• (KLi)TaO₃

Acknowledgments

One of the authors H.Y. is grateful for the support of Grants-in-Aid for JSPS fellows of MEXT, Japan and the 21st century COE program “Physics of systems with self-organization composed of multi-elements” of MEXT.