Fabrication and Evaluation of One-Axis Oriented Lead Zirconate Titanate Films Using Metal–Oxide Nanosheet Interface Layer

Abstract

Nanosheet Ca2Nb3O20 (ns-CN) layers with pseudo-perovskite-type crystal configuration were applied on the surface of polycrystalline metal substrates to achieve preferential crystal orientation of Pb(Zr,Ti)O3 (PZT) films for the purpose of enhanced ferroelectricity comparable to that of epitaxial thin films. PZT films with tetragonal symmetry (Zr/Ti=0.40:0.60) were fabricated by chemical solution deposition (CSD) on ns-CN-buffered Inconel 625 and SUS 316L substrates, while ns-CN was applied on the the substrates by dip-coating. The preferential crystal growth on the ns-CN layer can be achieved by favorable lattice matching between (001)/(100)PZT and (001)ns-CN planes. The degree of (001) orientation was increased for PZT films on ns-CN/Inconel 625 and ns-CN/SUS 316L substrates, whereas randomly-oriented PZT films with a lower degree of (001) orientation were grown on bare and Inconel 625 films. Enhanced remanent polarization of 60 µC/cm2 was confirmed for the PZT films on ns-CN/metal substrates, ascribed to the preferential alignment of the polar [001] axis normal to the substrate surface, although it also suffered from higher coercive field above 500 kV/cm caused by PZT/metal interfacial reaction.

Polar-axis-oriented crystal growth of tetragonal PZT films on stainless steel substrate using pseudo-perovskite nanosheet buffer layer

“…15,16,18,21 The nanosheets consisted of rectangular crystallites with thicknesses of approximately 2 nm and lateral sizes of approximately several hundred nanometers that expose the (001) plane of pseudo-perovskite-type lattice normal to the sheet surfaces [see high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and electron diffraction (ED) images in Fig. 1].…”

“…The Pt layer was applied as a diffusion barrier as well as a bottom electrode. 21 Ferroelectric PZT films with thickness of approximately 300 nm and Zr/Ti ratio = 40/60, Pb(Zr 0.40 Ti 0.60 )O 3 , were fabricated on ns-CN-supported Pt/SUS (ns-CN/Pt/SUS) and Pt/SUS by a conventional chemical solution deposition (CSD) technique. Detail of the CSD coating was reported elsewhere.…”

“…Detail of the CSD coating was reported elsewhere. 21 The crystal orientation of the films was confirmed by X-ray diffraction (XRD) using a Rigaku RINT2000 diffractometer (for 2θ − ω scan) and Philips X'Pert PRO MRD high resolution X-ray diffractometer equipped with an X-ray convergent poly capillaries (X-ray Lens) as an incident beam conditioner (for reciprocal space mapping). The dielectric and ferroelectric properties were evaluated using an Agilent technology 4294A impedance analyzer and a Toyo FCE-3 ferroelectric system, respectively.…”

“…Some researchers have reported successful results (e.g., using CeO 2 /YSZ or SrTiO 3 buffer layers, 4,7,12 or one-axis-oriented (100)LaNiO 3 template 13,14 ) in which the preferential c-/a-domain formation was realized together with the variation of their ferroelectric/piezoelectric properties. Single-crystal nanosheets of calcium niobate (Ca 2 Nb 3 O 10 ) that possess a pseudo-perovskite-type crystal structure 15,16 are currently being utilized for the buffer layers to control the crystal orientation of perovskite-or layer-perovskite-type dielectric films (SrTiO 3 21 etc.) because of its suitable unit cell size (lattice parameter: a = 0.3853 nm, b = 0.3868 nm) and convenient coating process by dip coatings using aqueous dispersion.…”

Fabrication of (100)_c-oriented Mn-doped bismuth ferrite films on silicon and stainless steel substrates using calcium niobate nanosheets

“…Such ns-CN-coated glass substrates have been fabricated for achieving preferential crystal growth of (100)SrTiO 3 films 18) and (100)PZT/(100)LaNiO 3 heterstructures. 19) Furthermore, our group has reported that the ns-CN layer aligned the crystal orientation of PZT (simple perovskite) 20) and SrBi 4 Ti 4 O 15 (layered perovskite) films 21) on platinized silicon and stainless steel substrates. We expected the ns-CN layer would also align the crystal orientation of the BFO-and related materials because the unit size of BFO is significantly close to that of ns-CN.…”