The dc field dependence of dielectric permittivity in Pb(Sc1/2Ta1/2)O3 (PST) has been investigated near room temperature. The phase boundary on the temperature–field phase diagram in PST has been determined, where the ferroelectric critical endpoint (CEP) under the dc field applied along the [111]c direction (in the cubic coordinate) has been estimated to be between 20 and 25 °C. A high dielectric tunability of 92% in the field of 20 kV/cm along the [111]c direction has been obtained at 20 °C. The dielectric tunability above the critical temperature in the case of the first-order phase transition has been discussed on the basis of the Landau theory.
The temperature–field phase diagram and the temperature dependence of the spontaneous polarization in Pb(Sc1/2Ta1/2)O3 (PST) have been investigated by measuring the permittivity in the dc biasing field and observing the p–E hysteresis loop, respectively. X-ray diffraction studies to clarify the B-site cation ordering have also been performed. We have confirmed the PST single crystal used in our experiment to be a disordered PST. We have also determined that the ferroelectric critical endpoint (CEP) on the temperature–field phase diagram in the dc biasing field applied along the [111]c direction (in the cubic coordinate) was at 19.3 °C and 4.85 kV cm−1. Our experimental results of the ferroelectric CEP and the spontaneous polarization in disordered PST are discussed in this paper on the basis of the Landau-type phenomenological theory.
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