Field-induced sharp ferroelectric phase transition in ${\mathrm{K}}_{0.937}$${\mathrm{Li}}_{0.063}$${\mathrm{TaO}}_3$

Sharp first-order ferroelectric phase transitions as indicated by sharp peaks of the dielectric permittivity arise in ${\mathrm{K}}_{0.937}$ ${\mathrm{Li}}^{0.063}$ ${\mathrm{TaO}}_3$ upon cooling or heating in electric fields 75<E<300 kV/m. They cancel the random dipolar fields due to frozen-in off-center ${\mathrm{Li}}_{+}$ ions, which destroy the phase transition and give rise to low-temperature domain states if E=0. Sharp zero-field transitions with a dispersionless peak of ε’ at ${\mathrm{T}}_{\mathrm{c}}^{+}$=104.5 K, which accurately follows the Landau-Devonshire theory at T<${\mathrm{T}}_{\mathrm{c}}^{+}$, are observed after field cooling with E>75 kV/m.