Reentrant Dipole Glass-Like Ordering in Weakly Concentrated KTaO₃:Nb

Abstract

Recently we reported that a very small admixture of Li^☎ dipole impurities into moderately concentrated KTaO₃:Nb leads to an unusual sequence of ferroelectric-type phase transitions with a reentrant glass phase formation at the lowest temperatures [1], Here, we present dielectric permittivity and Raman scattering study for nearly the same composition as used in Ref. [1], but without Li admixture, for KTa_0.982Nb_0.018,O₃ (KTN1.8). It is found that the presence of strong Li dipole defects is not an essential condition for the reentrant glass formation. Above T_c (27 K) KTN1.8 behaves as a conventional soft mode displacive type ferroelectric in paraelectric phase. However, below T_c a crossover to the order-disorder polar microregion dynamics and a state at which a reentrant glass phase coexists with long-range ordering occurs.

Keywords:

• Impurities
• Phase transitions
• Permittivity
• Raman scattering