Broadband dielectric spectroscopy of mixed $CuInP_2(S_xSe_{1-x})_6$ crystals

TL;DR

This study used broadband dielectric spectroscopy to map the phase diagram of mixed CuInP$_2$(S$_x$Se$_{1-x}$)$_6$ crystals, revealing asymmetric ferroelectric and dipolar glass phases, including relaxor behavior at phase boundaries.

Contribution

First comprehensive dielectric spectroscopy analysis of CuInP$_2$(S$_x$Se$_{1-x}$)$_6$ crystals, establishing their phase diagram and phase transitions.

Findings

Asymmetric phase diagram with flat ferroelectric transition decrease

Observation of dipolar glass phase in middle composition range

Nonergodic relaxor phase at boundary regions with small sulphur content

Abstract

In this article mixed CuInP$_2$(S$_x$Se$_{1-x}$)$_6$ crystals were investigated by broadband dielectric spectroscopy (20 Hz - 3 GHz). The complete phase diagram has been obtained from these results. The phase diagram of investigated crystals is strongly asymmetric - the decreasing of ferroelectric phase transition temperatures in CuInP$_2$(S$_x$Se$_{1-x}$)$_6$ is much more flat with small admixture of sulphur then with small admixture of selenium. In the middle part of the phase diagram (x=0.4-0.9) the dipolar glass phase has been observed. In boundary region between ferroelectric order and dipolar glass disorder with small amount of sulphur (x=0.2-0.25) at low temperatures the nonergodic relaxor phase appears. The phase diagram was discussed in terms of random bonds and random fields.