Electric field induced critical points and field gradient by trapped electrons in Li-doped KTa1-xNbxO3 single crystals

Abstract

The effects of electric field and trapped electrons on a ferroelectric phase transition of the 5%Li-doped KTa0.74Nb0.26O3 crystals were investigated by micro-Brillouin scattering and dielectric measurements. In micro-Brillouin scattering, the remarkable changes of the central peak (CP) intensity were observed at the paraelectric cubic to ferroelectric tetragonal phase transition. The critical electric fields to induce the paraelectric to ferroelectric phase transition were found to shift to higher values with increasing temperature. From these CP results, we estimated lines of critical points for phase transitions including critical end point (CEP), (E, T) = (1.6 kV/cm, TC-T+3.4 °C) in the composition-temperature-electric field (x-T-E) phase diagram. The clear difference of the CEP was observed between Brillouin result at a fixed small area and dielectric result averaged over all area of a sample. It can be caused by the field gradient, which is induced by the trapped electrons. The existence of gradient of electric field was also discussed using the observed result of position dependence of the CP intensity.

Brillouin Scattering Study of Electro-Optic KTa1−xNbxO3 Crystals

“…A study of the temperature dependence of the CP behavior was carried out to show the effect of injected electrons on the CEP. In this study, titanium electrode pairs were used to inject electrons into the KLTN/0.05/0.26 crystals by the application of voltages along the [ 100 ] direction [ 116 ]. The electric voltage dependence of the CP intensity at some selected temperatures of the KLTN/0.05/0.26 crystal in the paraelectric cubic phase is shown in Figure 11 a [ 116 ].…”

“…In this study, titanium electrode pairs were used to inject electrons into the KLTN/0.05/0.26 crystals by the application of voltages along the [ 100 ] direction [ 116 ]. The electric voltage dependence of the CP intensity at some selected temperatures of the KLTN/0.05/0.26 crystal in the paraelectric cubic phase is shown in Figure 11 a [ 116 ]. Significant variation in the intensity of the CP was found at the critical voltages, reflecting the paraelectric cubic to the ferroelectric tetragonal phase transition.…”

“…We also studied the position dependence of the Brillouin scattering spectra of the KLTN/0.05/0.26 crystal to clarify the effect of trapped electrons on the critical voltages. Figure 11 g shows a schematic illustration of three positions in the crystal [ 116 ]. The electric voltage dependence of the CP intensity at three positions is shown in Figure 11 d–f.…”

“…The detailed calculation procedure of the position-dependent critical electric field was reported in Ref. [ 116 ]. Figure 11 h shows the position dependence of the critical field of the KLTN/0.05/0.26 crystal.…”

Low DC Electric-Field-Induced Phase Transition in KTa0.59Nb0.41O3 Crystal

“…Potassium tantalate niobate, KTa 1– x Nb x O 3 (KTN) crystals, a solid solution of potassium tantalate and potassium niobate, have attracted much attention for their large linear and quadratic electro-optic coefficients, , photorefractive properties, and ferroelectric properties. , The ferroelectric properties and phase evolution of KTN crystals can be controlled by the ratio of Ta/Nb . Recently, the phase transitions including cubic to tetragonal phase, tetragonal to orthorhombic phase, and orthorhombic to rhombohedral phase in perovskite structure crystals have been studied by measuring their relative permittivity, ,− Fröhlich entropy, , and Raman spectrum. , Due to their practical device applications, many efforts are focused on cubic (paraelectric) to tetragonal (ferroelectric) phase transition which occurs at room temperature. − Among these works, the deformation of electric displacement–electric field ( D – E ) hysteresis curve from single curved line to double hysteresis loops, was considered as the indicator of cubic to tetragonal phase transition ( P C–T ) induced by electric field. However, the conventional D – E hysteresis curves only present averaged values over time and spatial domains and thus provide a general assessment of the resultant phase transition.…”