Mechanism of the Phase Change in PbK2LiNb5O15: Dielectric, structural, and Raman scattering studies

TL;DR

This study investigates the phase transition mechanisms in PbK2LiNb5O15, revealing a complex interplay of displacive and order-disorder behaviors associated with its ferroelectric and ferroelastic phases through dielectric, structural, and Raman scattering analyses.

Contribution

It provides new insights into the complex structural and phase change mechanisms in PbK2LiNb5O15, combining multiple experimental techniques to elucidate its ferroelectric and ferroelastic behavior.

Findings

Identification of paraelectric and ferroelectric phases with different symmetries.

Evidence of a displacive and order-disorder mechanism in phase transition.

Observation of a low frequency Raman mode without a clear soft mode.

Abstract

Experiments reveal that PbK2LiNb5O15 which belongs to the tetragonal tungsten bronze family presents paraelectric and ferroelectric phases and a complex structural change between them. High and low temperature phases are of symmetry P4/mbm and Pba2 respectively, so that this change is also of ferroelastic type. As presented here, crystallographic results hint at a displacive character of the ferroelectric ordering but show a more complex behaviour, with a clear order-disorder mechanism which accompanies the appearance of ferroelasticity. To complete our knowledge of this material, we have performed Raman experiments which exhibit a low frequency mode, but no clear soft mode is observed.