Ferroelectric, piezoelectric, and leakage current properties of (K0.48Na0.48Li0.04)(Nb0.775Ta0.225)O3 thin films grown by pulsed laser deposition

Abstract

Lead-free ͑K 0.48 Na 0.48 Li 0.04 ͒͑Nb 0.775 Ta 0.225 ͒O 3 ͑KNLNT͒ thin films were deposited on Pt͑111͒ / Ti/ SiO 2 / Si͑001͒ substrates using pulsed laser deposition. The film exhibited a well-defined ferroelectric hysteresis loop with a remnant polarization 2P r of 22.6 C / cm 2 and a coercive field E c of 10.3 kV/mm. The effective piezoelectric coefficient d 33,f of the KNLNT thin films was found to be about 49 pm/V by piezoelectric force microscope. The dominant conduction mechanisms of Au/KNLNT/Pt thin film capacitor were determined to be bulk-limited space-charge-limited-current and Poole-Frenkle emission at low and high electric field strengths, respectively, within a measured temperature range of 130-370 K. © 2011 American Institute of Physics. ͓doi:10.1063/1.3535608͔Because of the increasingly environmental concerns and legislations against the use of lead-based piezoelectric materials in the immediate future, great efforts have been made to develop high performance lead-free piezoelectric materials. 1Among them, ͑K 1−x Na x ͒NbO 3 ͑KNN hereafter͒ is considered to be a promising candidate owing to its pronounced ferroelectric and piezoelectric properties, high Curie temperature, and biocompatible nature. KNN thin films have been grown on various substrates by both physical and chemical approaches.2-8 Pioneer works on thin film KNN materials were mainly focused on undoped compositions in the vicinity of morphotropic phase boundary ͑MPB͒. Good ferroelectricity and high resistivity at low electric field were reported.8 Recent breakthrough in the textured highly piezoelectric Li, Ta, Sb doped KNN ͑KNN-LT-LS͒ ceramics by Saito et al. 9 has triggered intensive studies on KNN-LT-LS based thin films. [10][11][12] In spite of relatively high ferroelectric and piezoelectric properties, the films yet suffered from a high leakage current ͑e.g., Ͼ10−1 A / cm 2 @10 kV/ mm͒ and details of conduction mechanisms remain unclear. Indeed, the participation of toxic Sb in KNN-LT-LS system does not meet the ecological strategy of development of lead-free piezoelectrics.Ours and Hollenstein's studies 13,14 have revealed that Li + and Ta 5+ dual dopants can dramatically enhance the piezoelectric properties of KNN ceramics. The specific composition ͑K 0.48 Na 0.48 Li 0.04 ͒͑Nb 0.775 Ta 0.225 ͒O 3 ͑KNLNT hereafter͒ possesses optimal piezoelectric properties at room temperature due to the coexistence of tetragonal and orthorhombic phases. This MPB-like behavior and less processing and compositional complexity, especially the absence of toxic Sb content, as compared with KNN-LT-LS, have made KNLNT a promising candidate for biocompatible piezoelectric device applications. In this letter, we reported the excellent ferroelectric and piezoelectric properties, and low leakage current density in KNLNT thin films grown by pulsed laser deposition ͑PLD͒. Conduction mechanisms of the KNLNT thin films were investigated in detail.The stoichiometric target of KNLNT used for laser ablation was fabricated by the conventional solid state reaction...

Microstructure-dependent leakage-current properties of solution-derived (K0.5Na0.5)NbO3 thin films

“…The latter conduction mechanism could be described using the space-charge-limited current (SCLC) model (˛∼2, in the case of shallow traps [19]). Similar behaviour, i.e., showing ohmic conduction and SCLC as the dominant mechanisms at low fields, was previously reported for KNN-based thin films [13,20,21]. At E > 100 kV/cm, an abrupt increase was observed, with slope values much higher than 2, which presumably indicates the presence of deep traps in the material [22].…”

Effect of A-site Excess on the Piezoelectric Properties of (K0.48Na0.52)1+x(Nb0.55Ta0.45)O3Thin Films

“…So, according to the XRD patterns, the piezoelectric response increases with the increase in the F factor of KNNT thin films and films with high preferential (001) orientation exhibit large piezoelectric coefficient. For PZT thin films, the d 33,f value varies from 10 to 110 pm/V [27][28] [29] and for KNLNT thin films produced by PLD the piezoelectric coefficient d 33,f = 49 pm/V [30]. These results indicate that KNNT thin films are good candidates for lead-free piezoelectric thin films.…”

Potassium‐Sodium‐Niobate‐Based Thin Films: Lead Free for Micro‐Piezoelectrics

“…At the meantime, other substitutions, such as Ca, Ba, and Zr, which are commonly used in KNN‐based ceramics, were also confirmed to enhance the piezoelectricity of KNN film …”