Field-induced effects and ferroelectric critical endpoint in (K0.95Li0.05)(Nb1–x Ta x )O₃single crystals

Dielectric permittivities under dc biasing fields in the temperature range between –169 °C and 75 °C have been investigated in (K 0.95 Li 0.05 )(Nb 1– x Ta x )O 3 (KLNT– x , x = 71% and 74%). Field-induced ferroelectric phase transitions in KLNT– x have been clarified in the dc field applied along the [001] c direction (in the cubic coordinate). The ferroelectric critical endpoints in KLNT–71% and KLNT–74% have been determined to be 43.5 °C, 3.0 kV cm −1 , and 30.3 °C, 2.0 kV cm −1 , respectively. The tricritical point at which the first-order phase transition changes to the second-order phase transition has been estimated at 10.4 °C and x = 77.4% in the temperature–concentration phase diagram. The field-induced phase transitions and dielectric tunabilities have been discussed on the basis of the Landau-type free energy density.