TiO3 BaTiO3 Thin Films Research Articles

Ferroelectric and piezoelectric response in (100)-oriented Mn-doped Bi0.5Na0.5TiO3–BaTiO3 thin films

In this work, high-quality Mn-doped 0.935Bi0.5Na0.5TiO3–0.065BaTiO3 (Mn-BNBT) ferroelectric film was prepared on the SrRuO3-buffered (100)-oriented SrTiO3 single-crystal substrate using pulsed laser deposition method. The phase structure, morphology, domain and electrical properties were studied. Large remnant polarization Pr up to 35 μC/cm2, moderate dielectric constant ɛ33 /ɛ0 of 800 and low dielectric loss tanδ of 0.037 at 1 kHz was obtained at room temperature along with excellent local piezoelectric response. The temperature dependence of the ferroelectric hysteresis loop measurements indicates the ferroelectric long-range order can be sustain as high as 150 °C. The excellent global properties make the present Mn-BNBT thin film quite potential in environmental-friendly piezoelectric integrated device applications.

Excellent thermal stability of large polarization in (Bi0.5Na0.5)TiO3-BaTiO3 thin films induced by defect dipole

This work reports the large saturation polarization (Pm) of ~80 µC/cm2 and remnant polarization (Pr) of ~60 µC/cm2 in Mn-doped (Bi0.5Na0.5)TiO3-BaTiO3 (BNBTMn) thin films at elevated temperatures, which are substantially higher than the best values of the bulk counterparts, i.e. Pm (~40 µC/cm2) and Pr (~30 µC/cm2). The positive-up-negative-down (PUND) data suggested the contribution of switchable ferroelectric Pr is less than 50% in the overall Pr obtained in P-E loops at 300 K and keeps decreasing when heating. Thus, the observed large and thermally stable macroscopic polarizations in P-E loops is mainly attributed to the contribution of conformed local defect dipoles, namely MnTi′-Vo•• (oxygen vacancy), under a strong electric field. The evolution of Raman spectra with temperature further confirm the presence of symmetry breaking associated with local polar in our BNBTMn thin films can be remained up to 750 K, much higher than previous reported Curie temperature. This work will shed light on the development of high-temperature nano-scale ferroelectric memories and other related devices with eco-friendly materials.

Influence of oxygen pressure on the electrical properties of Mn-doped Bi0.5Na0.5TiO3BaTiO3 thin films by pulsed laser deposition

Ferroelectric Mn-doped 0.935Bi 0.5 Na 0.5 TiO 3 -0.065BaTiO 3 (MnBNBT) thin films were fabricated on (111)Pt/Ti/SiO 2 /Si substrates via pulsed laser deposition under different oxygen pressures. (100)-preferred orientation and dense films with perovskite structure were grown. The MnBNBT thin film deposited at an optimized oxygen pressure of 25 Pa exhibited a well-defined ferroelectric P - E loop with an average remnant polarization P r of 27 μC/cm 2 , a coercive field E c of 5.7 kV/mm, and a high relative dielectric constant of 1295. The leakage current characteristics were assessed, demonstrating that the ohmic conduction behaviors and Fowler-Nordheim tunneling were the main mechanisms of the MnBNBT thin films. Piezoelectric force microscopy indicated that the MnBNBT films possessed favorable local piezoelectric responses and multidomain states. The results suggest that the lead-free thin film produced is potentially applicable in ferroelectric and piezoelectric devices.

Temperature and composition dependent phase transitions of lead-free piezoelectric (Bi0.5Na0.5)TiO3-BaTiO3 thin films.

Extensive studies on (Bi0.5Na0.5)TiO3-BaTiO3 piezoceramics have aroused growing interest in developing high-performance piezoelectric films based on this promising lead-free piezoelectric system. High quality (1 - x%) (Bi0.5Na0.5)TiO3-x% BaTiO3 (x = 0-15) thin films were synthesized on Pt(111)/Ti/SiO2/Si(100) substrates via a sol-gel method. The phase transitions as functions of composition and temperature were investigated by X-ray diffraction (XRD) and temperature-dependent Raman spectra analysis. A morphotropic phase boundary (MPB) located at 5 ≤ x ≤ 10 was found in the films, being identical to that in bulk materials. Additionally, complicated structural changes with temperature in a wide composition range were observed, which correspond to the evolution from a low-symmetry ferroelectric phase or a relaxor phase to high-symmetry relaxor phases. The ferroelectricity and piezoelectricity were also systematically studied with an emphasis on the influence of composition and phase structure. A phase diagram focusing on the above two kinds of phase transitions has been proposed in this work.

Effect of annealing temperature on piezoelectric and mechanical properties of (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3–BaTiO3 thin films

Polycrystalline piezoelectric lead-free 85mol% (Bi0.5Na0.5)TiO3–10mol% (Bi0.5K0.5)TiO3–5mol% BaTiO3 (85BNT–10BKT–5BT) thin films were fabricated at different annealing temperatures by a chemical solution deposition method on Pt/Ti/SiO2/Si substrates. Perovskite phase was achieved during annealing at 650–800°C. The effect of annealing temperature on piezoelectric and mechanical properties was investigated. The results show that 85BNT–10BKT–5BT thin films annealed at 700°C exhibit the largest effective d33 value of 140.4pm/V, and the highest elastic modulus 142.0GPa. The optimal properties can be attributed to dense domain and homogenous microstructure. Results show that 85BNT–10BKT–5BT thin films may be a good candidate for lead-free piezoelectric-based micro-electromechanical systems.

Preparation and piezoelectric properties of self-polarized (Na,Bi)TiO3–BaTiO3 thin films on Si substrate

The c-axis oriented polycrystalline thin film of (Na,Bi)TiO3–BaTiO3 (NBT–BT) around the morphotropic phase boundary (MPB) was prepared on an LaNiO3-buffered Si substrate by rf magnetron sputtering. The NBT–BT film showed a large crystal lattice distortion in the out-of-plane direction, and a voltage shift of the hysteresis loop along the negative field axis as large as −200 kV/cm, which indicates that the film is internally biased and strongly self-polarized towards the top electrode. Owing to the large internal bias field, the NBT–BT film exhibited a linear piezoelectric response with the piezoelectric coefficient, , reaching −4.8 C/cm2 in the unipolar excitation and a low dielectric permittivity of 230. The temperature-dependent dielectric properties revealed that the permittivity maximum temperature, Tm, of the NBT–BT film was significantly enhanced to ∼550 °C from the ∼300 °C of bulk NBT–BT, accompanied by the disappearance of the depolarization temperature, Td, which is confirmed by the structural data where the crystal lattice remained unchanged up to ∼400 °C. These stable temperature properties would lead to an expansion of the temperature range of use of NBT–BT film.

Effect of Rb doping on ferroelectric and piezoelectric properties of Bi0.5Na0.5TiO3–BaTiO3 thin films

Rb doped 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNT–BT–Rbx) thin films with xmol% Rb (x=0, 2.5, 5, 7.5, 10) were deposited on Pt/Ti/SiO2/Si substrate by metal-organic solution deposition method. Experiments were conducted to investigate the effect of Rb doping on phase formation, microstructure, leakage current, and the resulting ferroelectric and piezoelectric property. It was found that substantial enhancement in structural, morphological and electrical properties can be achieved by Rb doping of BNT–BT thin films. Optimal electrical properties were obtained for 5mol% Rb doped BNT–BT thin films, with a dielectric constant, remnant polarization, and effective piezoelectric constant of ∼681, ∼28.9μC/cm2 and ∼86pm/V, respectively. It was suggested that the enhanced electrical properties in the case of 5mol% Rb BNT–BT thin films can be attributed to domain wall movement induced by A-site substitutions, large grain size, and lattice distortion.

Ferroelectric and piezoelectric properties of lead-free Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BaTiO3-thin films near the morphotropic phase boundary

Abstract Lead-free Bi0.5Na0.5TiO3 (BNT)–Bi0.5K0.5TiO3 (BKT)–BaTiO3 (BT) piezoelectric thin films with compositions near the morphotropic phase boundary (MPB) were deposited by metal-organic solution deposition on Pt/Ti/SiO2/Si (1 0 0) substrates. The compositional dependences of their microstructure and ferroelectric/piezoelectric properties were investigated. The results indicated that all the thin films have a single-phase perovskite structure and show outstanding electrical properties at room temperature. We found that the thin film with a composition of 0.884BNT–0.08BKT–0.036BT showed the best structural and electrical properties, with a dielectric constant, remnant polarization, and effective piezoelectric constant of ∼638, ∼27 μC/cm2 and ∼79 pC/N, respectively. We suggest that these superior properties are due to this sample’s high degree of alignment of ferroelectric domains in the MPB region and largest grain size.

Dielectric and ferroelectric properties of (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3–BaTiO3 thin films deposited via chemical solution deposition

Polycrystalline ferroelectric lead-free 85mol% (Bi0.5Na0.5)TiO3–10mol% (Bi0.5K0.5)TiO3–5mol% BaTiO3 (85BNT–10BKT–5BT) thin films were fabricated via chemical solution deposition on platinized silicon substrates. The permittivity and dielectric loss at 1kHz were 610 and ∼3.5%, respectively. The ferroelectric properties at room temperature and as a function of the temperature up to 125°C were also investigated. The polarization hysteresis loop at room temperature showed a PMAX of 31μC/cm2 and Pr of 6μC/cm2 at 200Hz. The shapes of the hysteresis loops at room temperature and 125°C were nearly identical, indicating good temperature stability. A dense surface morphology was observed and cross sectional microscopy revealed equiaxed grain growth. Based on these measurements, 85BNT–10BKT–5BT thin films may be a good candidate for lead-free piezoelectric-based microelectromechanical systems (MEMS).

Thermo-electrical energy conversions in Bi0.5Na0.5TiO3–BaTiO3 thin films prepared by sol–gel method

Solid solution (1−x)Bi0.5Na0.5TiO3–xBaTiO3 (BNT–xBT) thin films with x=0, 0.1, 0.9 and 1.0 are synthesized by sol–gel method. The as-prepared BNT–xBT films are crystallized into a single perovskite phase. The temperature-dependent polarizations of the thin films are measured to characterize their performances in thermo-electrical energy conversions. In BNT–0.1BT it is found that the electro-caloric refrigeration temperature change is 3.3°C with the application of an electric field of 862kV/cm at 46°C. The density of electrical energy generating from a 10°C temperature variation cycle is 0.68J/cm3. The results demonstrate that BNT–0.1BT lead-free ferroelectrics are excellent environmental-friendly energy materials for electro-caloric refrigeration and pyroelectric energy harvesting applications near room temperature.