Colossal Dielectric Permittivity in Tetragonal Pb(Fe1/2Nb1/2)1-xTixO3 Single Crystals

It has been a goal to find high dielectric permittivity and Curie temperature in high-strain crystals to enhance piezoelectric coefficient and thermal stability. Dielectric permittivity has been measured as functions of temperature and frequency in (001)-cut Pb(Fe_1/2Nb_1/2)_1-xTi_xO₃ (PFNTx) single crystals with starting composition at x=0.48. The tetragonal PFNT single crystals exhibit giant dielectric permittivity, high Curie (or depolarization) temperature, and low electric resistance, which are sensitive to Fe ion content, measured frequency, and thermal annealing treatment. A first-order-type tetragonalrarrcubic phase transition takes place at T_Ccong515 K. Ac electric conductivity increases with temperature dramatically, likely due to vacancy hopping and valance reduction of Fe3+ to Fe2+ ions. This study suggests that Fe ion is a promising candidate for dopant to enhance dielectric permittivity and depolarization temperature in Pb(Mg_1/3Nb_2/3)_1-xTixO₃ (PMNT) and Pb(Zn_1/3Nb_2/3)_1-xTixO₃ (PZNT) crystals.