Dielectric Properties of SrTiO3at Low Temperatures

Abstract

We have measured the temperature dependence of the dielectric constants for singledomain SrTi0 3 crystals. Dielectric anisotropics and deviations from the simple Curie-Weiss law have been observed and are discussed in connection with the structural phase transitions at 110 and 65°K.The structural phase transition at T a~ 110°K in SrTi0 3 is a direct consequence of the condensation of the r 25 optical-phonon mode at the Brillouin-zone boundary. 1 " 4 The dielectric constant of this crystal was reported to obey a simple form, e = C(T-T c )~1 9 with paraelectric Curie temperature T C «35°K. At lower temperatures, an appreciable departure from the Curie-Weiss law was observed, which was ascribed to the quantum effect of ionic polarizability. 5 " 8 Hitherto, the dielectric properties were obscured by the presence of multiple domains when the crystal is cooled through T a . The nonferroelectric structural transitions were generally considered not to affect the dielectric behavior. Recently, it was demonstrated that a uniaxial compressive stress can produce a single-domain crystal at low temperatures. 9,10 We report here dielectric measurements on single-domain crystals produced by this technique.A tetragonal prism with surfaces of (110), (ITO), and (001) and of size 2x2x3 mm 3 was cut from a pure single crystal. Geometries of the crystal axes, electrodes for dielectric measurement, and the direction of compressive stress are shown in Fig. 1, Samples were always cooled from room temperature to liquid-helium temperature under an applied stress higher than 10 kg/ mm 2 and the stress was released during dielectric measurement in order to avoid the pressure dependence of the permittivity. This procedure (a) (b) (c) (d) FIG. 1. Geometries of crystal axes, electrodes, external uniaxial stress (thick arrows) and the direction of c axes in the sample (thin arrows), for measuring (a) e a , (b) € c , (c) € 110 , and (d) efo.Dielectric permittivity was measured by a threeterminal method using a GR model 1615A capacitance bridge at 10 kHz with a field level of 5 V/ cm. Temperature inside the sample cryostat was raised slowly, at the rate of 0.2°C/min.Components of the dielectric permittivity tensor for crystals subjected to the stress treatment were determined as functions of temperature, with results as shown in Fig. 2. In this figure we notice that the dielectric tensor becomes anisotropic below T a9 with e a larger than e c . Furthermore, the dielectric anisotropy in the plane perpendicular to the c axis was found to develop around T b ^65°K 12_14 ; that is, [110] and [1T0] axes I-i-i-i-i-|-i-i-i-i-|-i-i-i-i-|-i-i-i-r 0 50 100 150 200 TEMPERATURE (°K) FIG. 2. Temperature dependence of the dielectric constants in SrTi0 3 for various orientations (see Fig. 1). The insets show the details of the dielectric anisotropics near T a and T b9 respectively. 851

Thermally activated recovery of electrical conductivity inLaAlO3/SrTiO3

“…Therefore, it appears that the trapping sites are related to crystal imperfections of similar length scales. Possible candidates are dislocations that were found to reduce conductivity and mobility of the LAO/STO interface with unusual temperature dependence during warming which is reminiscent to our results [18], or twin boundaries in SrTiO 3 which form due to structural phase transitions of the STO [24][25][26].…”

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO3 Overlayers

“…The second channel, instead, could be further away from the interface, where a lessdefected STO determines a higher electron mobility. In this picture, the depopulation of ρ II might be linked to the drop of the STO dielectric constant upon warming [32] (Supplementary Fig. 6).…”

Tunable photovoltaic effect and solar cell performance of self-doped perovskite SrTiO3

“…An additional advantage of using STO single crystals in PV devices is the high dielectric constant (ε r ∼ 300 at room temperature, and it can reach 10 4 at low temperatures). 38 Such a high dielectric constant not only facilitates the formation of the depletion layer and the photogeneration of electron-hole pairs, but also reduces carrier scattering by screening charged defects, overall enhancing the PV efficiency.…”