Quantum paraelectricity and induced ferroelectricity by germanium doping of (PbySn1–y)2P2S(Se)6 single crystals

Abstract

In this paper we report a dielectric study on four single crystals Pb₂P₂S₆, (Pb_0.98Ge_0.02)₂P₂S₆, (Pb_0.7Sn_0.3)₂P₂S₆ + 5% Ge and (Pb_0.7Sn_0.3)₂P₂Se₆ + 5% Ge down to 20 K. A new quantum paraelectric state was reported in the Ge-doped samples at low temperatures. In all of these materials the non-classical T² temperature dependences of inverse dielectric permittivity were observed. The dielectric constants of Pb₂P₂S₆-based single crystals were measured between 20 and 300 K. The temperature dependences of dielectric permittivity were analysed on the basis of Barrett’s model as a signature of quantum paraelectricity.