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

In this paper we report a dielectric study on four single crystals Pb2P2S6, (Pb0.98Ge0.02)2P2S6, (Pb0.7Sn0.3)2P2S6 + 5% Ge and (Pb0.7Sn0.3)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.