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 Pb 2 P 2 S 6 , (Pb 0.9 8Ge 0.02 ) 2 P 2 S 6 , (Pb 0.7 Sn 0.3 ) 2 P 2 S 6 + 5% Ge and (Pb 0.7 Sn 0.3 ) 2 P 2 Se 6 + 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 T 2 temperature dependences of inverse dielectric permittivity were observed. The dielectric constants of Pb 2 P 2 S 6 -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.