Dielectric and ferroelectric properties of strain-relieved epitaxial lead-free KNN-LT-LS ferroelectric thin films on SrTiO3 substrates

Abstract

We report the growth of single-phase (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrRuO3 coated ⟨001⟩ oriented SrTiO3 substrates by using pulsed laser deposition. Films grown at 600°C under low laser fluence exhibit a ⟨001⟩ textured columnar grained nanostructure, which coalesce with increasing deposition temperature, leading to a uniform fully epitaxial highly stoichiometric film at 750°C. However, films deposited at lower temperatures exhibit compositional fluctuations as verified by Rutherford backscattering spectroscopy. The epitaxial films of 400–600nm thickness have a room temperature relative permittivity of ∼750 and a loss tangent of ∼6% at 1kHz. The room temperature remnant polarization of the films is 4μC∕cm2, while the saturation polarization is 7.1μC∕cm2 at 24kV∕cm and the coercive field is ∼7.3kV∕cm. The results indicate that approximately 50% of the bulk permittivity and 20% of bulk spontaneous polarization can be retained in submicron epitaxial KNN-LT-LS thin film, respectively. The conductivity of the films remains to be a challenge as evidenced by the high loss tangent, leakage currents, and broad hysteresis loops.

Lead-Free KNN-Based Piezoelectric Materials

“…For the films deposited at 750 C, a single perovskite phase with intense (001) oriented peaks is observed in the y-2y scan. The phi-scan of the (011) pole consists of four peaks separated by 90 which indicates the locking of in-plane orientational symmetry and confirms that the films are grown epitaxially [105].…”

“…At lower temperatures, the RBS profile shows a considerable discrepancy between the experimental and simulated data caused by low atomic mobility and higher surface roughness of the film [105].…”

“…With increasing the oxygen pressure, the domain wall mobility is made higher and the (110) pole of KNN-LT-LS for 600 and 750 C deposited films. A <001> oriented epitaxial thin film with single perovskite phase is achieved at 750 C [105] closer the A-site cation concentration comes to its ideal stoichiometry which results in a higher dielectric constant and spontaneous polarization [106]. Abazari et al reported that 1 mol% doping of KNN-LT-LS films increases the remnant polarization from 4 to 10 mC cm…”

“…As can be observed, at low temperatures (600 C), the film exhibits a columnar structure along the [001] direction pointing out of the surface of the film with a grain size of about 200 nm. By increasing the deposition temperature, the columnar grains coalesce and form a uniform dense structure with a smooth surface [105]. Figure 5.11 shows the XRD spectra and phi-scans of the (011) pole of KNN-LT-LS films deposited at different temperatures.…”

Properties of (K,Na)NbO3-based lead-free piezoelectric films prepared by pulsed laser deposition

“…2(d). The leakage current of Mn-doped KNN-KNT-LS and KNN-KNT-LS films reported in the literatures are two and five order magnitudes higher than our KNN-KNT-LT film, respectively [7,9]. Hence, the defect contributions to the polarization and dielectric constant should be small.…”