Quantum paraelectric state and critical behavior in Sn(Pb)$_2$P$_2$S(Se)$_6$ ferroelectrics

• Main Authors: Zamaraite, I, Liubachko, V, Yevych, R, Oleaga, A, Salazar, A, Dziaugys, A, Banys, J, Vysochanskii, Yu
• Format: Journal Article
• Language: English
• Published: 22-03-2020
• Subjects: Physics - Materials Science
• DOI: 10.48550/arxiv.2003.09966

The dipole ordering in Sn(Pb)$_2$P$_2$S(Se)$_6$ materials may be tuned by
chemical substitution realizing a ferroelectric quantum phase transition and
quantum glassy or relaxor type phenomena on different parts of the phase
diagram. The introduction of Ge impurity increases the temperature of the phase
transitions and initiates a more pronounced Ising type critical anomaly in
Sn$_2$P$_2$S$_6$ crystal, does not shift the coordinate of the Lifshitz point
$x_{\textrm {LP}}$ in Sn$_2$P$_2$(Se$_x$S$_{1-x}$)$_6$ mixed crystals, induces
the appearance of a ferroelectric phase transition in quantum paraelectrics
Pb$_2$P$_2$S$_6$ and inhomogeneous polar ordering in
(Pb$_{0.7}$Sn$_{0.3}$)$_2$P$_2$S(Se)$_6$ crystals. For Pb$_2$P$_2$S$_6$
crystal, the real part of the dielectric susceptibility in the quantum critical
regime varies as $1/T^2$ instead of the expected $1/T^3$ behavior for uniaxial
materials. This can be partially explained by a screening phenomenon in the
semiconductor materials of the Sn(Pb)$_2$P$_2$S(Se)$_6$ system, which weakens
the long range electric dipole interactions, and also provides, at high
temperatures, a critical behavior near the Lifshitz point (studied by thermal
diffusivity) similar to the one predicted in the case of systems with short
range interactions. At low temperatures, a quantum critical behavior in
Pb$_2$P$_2$S$_6$ crystal can be established by the nonlinear coupling between
polar and antipolar fluctuations. An increase in thermal conductivity is
induced by Ge impurity in Pb$_2$P$_2$S$_6$ crystal, which is explained through
the weakening of the acoustic phonons resonance scattering by soft optic
phonons because of the appearance of ferroelectric phase polar clusters.