Low-temperature dielectric behavior of disordered and ordered langasite family single crystals LGS, LGT, SNGS and STGS

Dielectric measurements of disordered La3Ga5SiO14 (LGS), La3Ga5,5Ta0,5O14 (LGT) and ordered Sr3NbGa3Si2O14 (SNGS), Sr3TaGa3Si2O14 (STGS) single crystals of the langasite family performed at frequencies from 10 Hz to 1 MHz at temperatures between 4.2 and 300 K are reported. Temperature dependences of dielectric permittivity ε33 and ε11 are obtained. It is shown that ε33 in LGS and LGT exhibits incipient ferroelectric-like behavior. SNGS and STGS demonstrate ordinary dielectric temperature dependences as dielectric permittivity decreases down to helium temperatures.