Lead‐Free Ferroelectric (Na_1/2Bi_1/2)TiO₃–BaTiO₃ Thin Films in the Morphotropic Phase Boundary Composition: Solution Processing and Properties

Abstract

Ferroelectric (Na1/2Bi1/2)TiO3–BaTiO3 (BNT–BT) single perovskite thin films have been prepared, for the first time, by chemical solution deposition onto Pt/TiO2/SiO2/(100)Si substrates. A solution process has been developed for the preparation of precursor solutions. The handling of all the chemical reagents, refluxes, and distillations was carried out in air. In addition, the resulting solutions are stable in air, presenting a low gelation and trend to the formation of precipitate. Solutions containing a 10 mol% of Na excess, and a 10 mol% excess of Na+10 mol% excess of Bi, were prepared. These solutions were spin‐coated onto the substrates, obtaining amorphous layers that were crystallized in O2 by rapid thermal processing. Multiple deposition and crystallization were carried out to grow crystalline films with a thickness between 125 and 140 nm. At temperatures below 600°C, the perovskite phase coexists with a pyrochlore phase. At temperatures over 700°C or soaking times over 60 s, an interdiffusion substrate/film interface is formed. Single perovskite BNT–BT thin films are obtained at 650°C, with soaking times of only 6 s. There is an effect of the Na excess and Na+Bi excess on the film microstructure and the dielectric/ferroelectric properties. The films containing Na+Bi excess have a larger grain size, higher dielectric permittivities (at room temperature K′∼400), and higher saturation and polarization values (Ps∼23 μC/cm2 and Pr∼12 μC/cm2). The results of this work prove the feasibility of preparing these lead‐free compositions in thin film form, resulting in materials with promising functional properties when integrated with Si semiconductor substrates.

Enhanced ferroelectric and piezoelectric properties in doped lead-free (Bi0.5Na0.5)0.94Ba0.06TiO3 thin films

“…[5][6][7] In spite of the numerous studies on BNT-based single crystals and ceramics, literature tackling with the growth and characterization of BNT-based, especially BNBT-based thin films, still remains at an infancy stage. [8][9][10][11][12] Consequently, doping effects on the electrical properties of thin film BNBT materials are still unclear. Abazari et al 13 has recently reported epitaxial potassium modified BNBT thin films grown on SrRuO 3 coated SrTiO 3 substrates by pulsed laser deposition ͑PLD͒.…”

Reduced leakage current and large polarization of Na0.5Bi0.5Ti0.98Mn0.02O3 thin film annealed at low temperature

“…No diffraction peaks of NBTMn can be detected in the film annealed at 450 °C, meaning that the film is amorphous. When the annealing temperature increases to 500 °C, the evident crystalline diffraction peaks of NBTMn thin film being observed, which is among the lowest heat treatment temperature in the NBT-based thin films ever reported [21,22]. This can be ascribed to the following two factors.…”

Investigation of thickness dependence of electric properties of sol–gel BNT–BT thin films with stepwise crystallization

“…10),12)17) BNTBT bulk ceramics show good dielectric (relative dielectric constant at room temperature of 1200 and maximum values of 7000), ferroelectric (remanent polarization of P r ³45¯C/cm 2 and coercive field of E c ³35 kV/cm), and piezoelectric (d 33 ³110 pC/N) properties in the MPB composition, which make BNTBT lead-free material attractive for applications in electronics. 16), 17) The thin film form of the piezoelectric materials exhibit lots of advantages for micro electromechanical systems (MEMS) owing to the large motions generated in films and high energy densities.…”

“…As reported, chemical solution deposition, 16), 19) pulse laser deposition, 1),20),21) RF magnetron sputtering, 22) metal organic decomposition 23) and solgel deposition 24) are among the most widely used methods to fabricate the BNTBT thin films. The solgel method can offer good stoichiometry control of the film composition.…”