English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

For CuInP$_2$S$_6$ layered ferrielectric crystal, that is most investigatedamong wide family of van der Waals ferroics MM$'$P$_2$X$_6$ (M - Cu, Ag; M$'$ -In, Bi, Cr, $\dots$; X - S, Se), by Brillouin spectroscopy the temperaturedependence of the longitudinal hypersound velocity was investigated for theacoustic phonons propagated in the plane of crystal layers. Pronouncedsoftening of acoustic phonon branch is observed in the paraelectric phase below$T^{*} \approx 330~$K at cooling to temperature $T_C \approx 312~$K of thefirst order phase transition into ferrielectric phase. Below $T_C$ thehypersound velocity growth in correlation with spontaneous polarization riseand its temperature anomaly is similar to earlier observed temperature behaviorof longitudinal ultrasound velocity for acoustic wave propagated normally tothe structural layers. Determined anomalous part of the CuInP$_2$S$_6$ crystalthermal conductivity in the vicinity of ferrielectric transition alsodemonstrate lowering of the heat transferring phonons group velocity withcooling from $T^{*}$ to $T_C$. Observed acoustic softening obviously is inducedby flexoelectric coupling of relaxational soft polar optic and acousticbranches that is related to inhomogeneously polarized state appearing betweenparaelectric and ferrielectric phases.

Phonon Spectra and Phase Transitions in van der Waals Ferroics MM$'$P$_2$X$_6$