BaTiO3 Thick Films Research Articles

Towards lower annealing temperatures and enhanced functional properties in aerosol-deposited piezoelectric thick films: A study of the effect of Li additive on BaTiO3 films

The effect of incorporating Li additive (Li2CO3) into aerosol deposited BaTiO3 thick films was investigated. The addition of Li2CO3 to the deposited powder facilitated grain growth during post deposition process, even for low annealing temperatures (≤ 700 °C). Therefore, this additive decreased the threshold for ferro/piezoelectricity recovery from 800 °C to 650 °C. Furthermore, annealing at temperatures ≥ 800 °C yielded grain sizes ranging from 100 nm to 700 nm, unprecedented in our previous investigations. Substantially improved ferroelectric and piezoelectric responses were obtained in the 800–900 °C range, with Pr values doubling to 12 µA.cm−2 for films annealed at 900 °C. Moreover, the use of this additive improved leakage behavior, achieving a leakage current density of 0.1 µA.cm−2 and an electrical resistivity of 1011 Ω.cm at 700 °C. Microscopic analyses revealed a carbon containing secondary phase at grain boundaries, probably corresponding to Li2CO3.

Preparation of Pb(Mg1/3Nb2/3)TiO3–PbTiO3 thick films with highly preferred orientation via screen printing

Rhombohedral 0.75Pb(Mg1/3Nb2/3)TiO3–0.25PbTiO3 (PMN-25PT) and tetragonal 0.65Pb(Mg1/3Nb2/3)TiO3–0.35PbTiO3 (PMN-35PT) thick films with a highly preferred orientation were prepared via screen printing on MgO and YSZ ceramic substrates. The use of oriented BaTiO3 thick films as template layers was effective in forming the oriented PMN-25PT and PMN-35PT thick films. The orientation degrees of both thick films were over 0.85. The formation process of the thick films was examined using electron backscatter diffraction. PMN-25PT grains grew on the BaTiO3 template layers and aligned with the BaTiO3 orientation direction. Finally, the PMN-25PT and PMN-35PT thick films prepared on MgO had better electrical properties than the thick films fabricated on YSZ.

Enhanced grain growth and dielectric properties in aerosol deposited BaTiO3

Piezoelectric ceramics are envisioned as cell stimulating materials for in-vivo, load-bearing applications. To compensate for their brittle nature developing ceramic films on medically accredited metals is a promising approach. However, high temperature consolidation is often required to achieve highly dense ceramics with suitable functional properties, which can compromise the metal substrate integrity. With aerosol deposition highly dense thick films can be produced at room temperature. Still, an annealing step is required to enhance the functional properties of piezoelectric ceramics. Thermal annealing of dense, aerosol deposited BaTiO3 thick films on 304SUS stainless steel gave a clear enhancement of the dielectric properties. An increase in saturation polarization and the adoption of ferroelectric hysteresis at 750 °C coincided with a significant reduction in mechanical properties. The simultaneous appearance of grain growth and diffusion of chromium from the substrate at 750 °C suggests that chromium acts as a sintering aid.

Grain engineering of high energy density BaTiO3 thick films integrated on Si

Ferroelectric (FE) ceramics with a large relative dielectric permittivity and a high dielectric strength have the potential to store or supply electricity of very high energy and power densities, which is desirable in many modern electronic and electrical systems. For a given FE material, such as the commonly-used BaTiO3, a close interplay between defect chemistry, misfit strain, and grain characteristics must be carefully manipulated for engineering its film capacitors. In this work, the effects of grain orientation and morphology on the energy storage properties of BaTiO3 thick films were systematically investigated. These films were all deposited on Si at 500 °C in an oxygen-rich atmosphere, and their thicknesses varied between ~500 nm and ~2.6 μm. While a columnar nanograined BaTiO3 film with a (001) texture showed a higher recyclable energy density Wrec (81.0 J/cm3vs. 57.1 J/cm3 @3.2 MV/cm, ~40% increase) than that of a randomly-oriented BaTiO3 film of about the same thickness (~500 nm), the latter showed an improved energy density at a reduced electric field with an increasing film thickness. Specifically, for the 1.3 μm and 2.6 μm thick polycrystalline films, their energy storage densities Wrec reached 46.6 J/cm3 and 48.8 J/cm3 at an applied electric field of 2.31 MV/cm (300 V on 1.3 μm film) and 1.77 MV/cm (460 V on 2.6 μm film), respectively. This ramp-up in energy density can be attributed to increased polarizability with a growing grain size in thicker polycrystalline films and is desirable in high pulse power applications.

Temperature‐induced changes of the electrical and mechanical properties of aerosol‐deposited BaTiO3 thick films for energy storage applications

AbstractAerosol deposition (AD) is a room‐temperature film deposition method for the fabrication of scalable ferroelectric ceramic films on different substrates, which is particularly appealing for thick film energy storage applications. However, the electrical and mechanical properties of AD ferroelectric films are not yet satisfactorily understood. Here, we report the dielectric, energy storage, and mechanical properties of aerosol‐deposited BaTiO3 (AD‐BT) thick films with nanosized grains by combining macroscopic electric measurements with indentation tests. We find that thermal annealing is an effective way to improve dielectric permittivity and polarization of the AD‐BT film, as well as to increase the hardness and Young's modulus of the film. However, crack formation in the annealed AD‐BT film is promoted in comparison to the as‐processed sample, suggesting that the interplay between the nanosized grains and release of the internal stress during annealing may have major consequences for the mechanical properties and hence should be taken into consideration in application.

Effect of MnO2 addition on temperature-dependent properties of tetragonal (Bi,Na)TiO3–BaTiO3 thick films prepared on MgO ceramic substrates

The temperature-dependent properties of the (1–x)(Bi0.5Na0.5)TiO3–xBaTiO3 (BNT–100xBT, 0.14 ≤ x ≤ 0.40) thick films with MnO2 additives were investigated. The addition of 0.2 wt% MnO2 to the thick films increased the remanent polarization (P r) and improved the temperature stability of the P r. The P r value of the thick films was comparable to that of the thick films with the morphotropic phase boundary (MPB) composition. The depolarization temperatures (T ds) were higher than those of bulk ceramics. The highest T d of ∼300 °C was observed in the BNT–20BT thick films with MnO2 addition. To understand the change in T d with a composition x, the thermal expansions of BNT–100xBT were examined.

Effect of substrate thermal expansion coefficients on the properties of (Bi,Na)TiO3–BaTiO3 thick films around the morphotropic phase boundary

Lead-free (1–x)(Bi0.5Na0.5)TiO3–xBaTiO3 (abbreviated as BNT–100xBT) thick films around the morphotropic phase boundary composition (0.03 ≤ x ≤ 0.09) were prepared on Pt-coated substrates with different thermal expansion coefficients, and the properties of the films were analyzed. While BNT–100xBT (x ≤ 0.05) exhibit a rhombohedral structure, BNT–100xBT (0.07 ≤ x) exhibit a tetragonal structure. The BNT–100xBT (0.03 ≤ x ≤ 0.09) thick films prepared on the MgO substrate preferentially formed c-domains. The Pr of the BNT–100xBT (0.03 ≤ x ≤ 0.09) thick films has the maximum value at the composition of x = 0.07 at room temperature. The depolarization temperature of the BNT–100xBT thick films prepared on MgO substrates with Pt bottom electrodes (0.05 ≤ x) was larger than that of the BNT–100xBT thick films prepared on 3 mol% Y2O3-stabilized ZrO2, Al2O3 substrates with Pt bottom electrodes, or bulk ceramics. An increase in the depolarization temperature became larger with an increase in composition of x because the thermal expansion difference between BNT–100xBT and MgO became large with an increase in the composition of x.

Effect of substrate material to the properties of screen-printed lead free (Bi0.5Na0.5)TiO3-based thick films

Lead-free piezoelectric 0.83(Bi0.5Na0.5)TiO3-0.17BaTiO3 (BNT-17BT) thick films were grown on MgO ceramic substrates via screen printing. Thick films with compressive stress formed a c-domain preferentially with a volume fraction of 0.88. High-temperature X-ray diffraction and piezoresponse force microscopy and the temperature dependence of the piezoelectric coefficient d33 data indicated that the thick films had a preferred c-domain during the transformation from the tetragonal phase to the cubic phase with temperature increasing. Based on polycrystalline MgO substrates with high thermal expansion coefficients, the thick films displayed a higher phase transition temperature and larger remanent polarization (Pr) values over 220 °C than those of thick films on Al2O3 substrates. The ferroelectric properties of BNT-17BT/MgO were better than those of soft PZT/YSZ and hard PZT/YSZ over 220 °C. The results showed the possibility of applying BNT-17BT thick films in a wide temperature range.

Fabrication of porous thick films using room‐temperature aerosol deposition

AbstractA novel technique for the rapid room‐temperature deposition of porous ceramic, glass, or metal thick films using the aerosol deposition (AD) method is presented. The process is based on the co‐deposition of the desired film material and a second water‐soluble constituent, resulting in a ceramic‐ceramic composite. Following the subsequent removal of water‐soluble end member, a network of pores is retained. To demonstrate the process, porous BaTiO3 thick films were fabricated through co‐deposition with NaCl. Microstructural images show the clear development of a porous structure, which was found to enhance the dielectric properties over dense thick films, possibly related to the lower extent of internal residual stress. This simple but highly effective porous structure fabrication can be applied to any film and substrate material stable in water and is promising for the application of AD‐processed films in gas sensors, solid oxide fuel cells, and humidity sensors.

Fabrication and Characterization of High-Frequency Ultrasound Transducers Based on Lead-Free BNT-BT Tape-Casting Thick Film.

A lead-free 0.94(Na0.5Bi0.5) TiO3-0.06 BaTiO3 (BNT-BT) thick film, with a thickness of 60 μm, has been fabricated using a tape-casting method. The longitudinal piezoelectric constant, clamped dielectric permittivity constant, remnant polarization and coercive field of the BNT-BT thick film were measured to be 150 pC/N, 1928, 13.6 μC/cm2, and 33.6 kV/cm, respectively. The electromechanical coupling coefficient kt was calculated to be 0.55 according to the measured electrical impedance spectrum. A high-frequency plane ultrasound transducer was successfully fabricated using a BNT-BT thick film. The performance of the transducer was characterized and evaluated by the pulse-echo testing and wire phantom imaging operations. The BNT-BT thick film transducer exhibits a center frequency of 34 MHz, a −6 dB bandwidth of 26%, an axial resolution of 77 μm and a lateral resolution of 484 μm. The results suggest that lead-free BNT-BT thick film fabricated by tape-casting method is a promising lead-free candidate for high-frequency ultrasonic transducer applications.

Preparation of 0.83(Bi0.5Na0.5)TiO3–0.17BaTiO3 thick films by screen printing

Preferentially oriented 0.83(Bi0.5Na0.5)TiO3–0.17BaTiO3 (BNT–17BT) thick films were prepared by adopting substrates with different thermal expansion coefficients, and the properties of the films were analyzed. The thick films were prepared by screen printing. The calcination temperature required to form BNT–17BT thick films without heterogeneous compounds was studied. The c-domain volume fraction (αc) of the BNT–17BT thick films prepared on 3 mol % Y2O3-stabilized ZrO2 (YSZ) substrates with Pt bottom electrodes (BNT–17BT/YSZ) was larger than that of the BNT–17BT thick films prepared on Al2O3 substrates with Pt bottom electrodes (BNT–17BT/Al2O3) because the BNT–17BT/YSZ exhibited greater compressive stress than the BNT–17BT/Al2O3. The temperature dependence curves of the dielectric constants of the bulk ceramics and BNT–17BT/Al2O3 showed a shoulder with frequency dispersion at approximately 200 °C, whereas this shoulder was not observed in the curves of the BNT–17BT/YSZ. The remanent polarization (Pr) of the BNT–17BT/YSZ was larger than that of the BNT–17BT/Al2O3. At temperatures higher than 180 °C, the Pr of the BNT–17BT/YSZ was larger than that of the bulk ceramics. The Pr of the BNT–17BT/YSZ was larger than that of the BNT–17BT/Al2O3 because the BNT–17BT/YSZ exhibited αc values larger than those of the BNT–17BT/Al2O3.

H2S Gas Sensing Properties of Sr Modified BaTiO3 Thick Films by Dipping and Doping Process

H₂S Gas Sensing Properties of Sr Modified BaTiO₃ Thick Films by Dipping and Doping Process

Electro-Optical Properties of Combined Dielectric Layers with BaTiO3 Thin Films Sputtered on BaTiO3 Thick Film

Electro-Optical Properties of Combined Dielectric Layers with BaTiO3 Thin Films Sputtered on BaTiO3 Thick Film

Effects of substrate materials on piezoelectric properties of BaTiO3 thick films deposited by aerosol deposition

Piezoelectric properties were evaluated for annealed BaTiO3 (BT) films formed by aerosol deposition on yttria-stabilized zirconia (YSZ) and Fe–Cr–Al-based heat-resistant stainless steel (SS). The piezoelectric constants d31 of BT films annealed at 1200 °C formed on YSZ and SS were −71 and −41 pm/V, respectively. The effects of different substrates on piezoelectric properties were investigated. The grain sizes of the films formed on YSZ and SS were 1.5 and 1.0 µm, respectively. X-ray diffraction analysis using a two-dimensional stress method revealed that the respective residual stresses of the films formed on YSZ and SS were −55 ± 8 and −32 ± 7 MPa, respectively, as compressive stresses. The c-domain structure was formed preferentially in the films on SS because of its larger compressive stress. These results suggest that differences in piezoelectric properties attributable to substrates result from differences in compressive stress magnitude and the volume fraction between the c- and a-domains.

Elaboration of lead-free Na0.5Bi0.5TiO3–BaTiO3 (NBT-BT) thick films by aerosol deposition method (ADM)

Thick and dense ceramic films of lead-free 0.94Na0.5Bi0.5TiO3-0.06 BaTiO3 (NBT-BT) composition were elaborated by aerosol deposition method (ADM) at room temperature. A powder of suitable grain size was elaborated by solid state reaction. Using this powder, two samples were elaborated by ADM respectively on glass and metallic substrates, in order to check for microstructure and electrical properties. This process allowed obtaining a thick film (3.2µm) with dense microstructure. Measurement of electrical properties revealed a lossy dielectric behavior indicating interfacial phenomena at the electrode–film interface. The measurement of the ferroelectric hysteresis cycle does not show any characteristics of a ferroelectric behavior, but corresponds well to the one of a lossy non-linear dielectric. The absence of ferroelectricity is probably due to the low grain size of the obtained thick film (130nm). Further experiments are in progress in order to try to obtain ferroelectric properties.

Growth of BaTiO3-PVDF composite thick films by using aerosol deposition

Barium titanate (BaTiO3)-polyvinylidene fluoride (PVDF) composite thick films were grown by using aerosol deposition at room temperature with BaTiO3 and PVDF powders. To produce a uniform composition in ceramic and polymer composite films, which show a substantial difference in specific gravity, we used PVDF-coated BaTiO3 powders as the starting materials. An examination of the microstructure confirmed that the BaTiO3 were well distributed in the PVDF matrix in the form of a 0 – 3 compound. The crystallite size in the BaTiO3-PVDF composite thick films was 5 ∼ 50 times higher than that in pure BaTiO3 thick films. PVDF plays a role in suppressing the fragmentation of BaTiO3 powder during the aerosol deposition process and in controlling the relative permittivity.

Preparation of BaTiO3-based thick films with c-axis-preferred orientation using screen printing

Pb(Zr,Ti)O3 and related materials have been lauded for their piezoelectric properties, but their toxicity has driven the search for alternative materials with the same high performance in electronic devices. Among these, BaTiO3-based materials are regarded as excellent substitutes. Using a screen printing method, in this study, we prepare BaTiO3 thick films on ZrO2 stabilized with 3 mol % Y2O3 (YSZ) or MgO ceramics with Pt bottom electrodes. BaTiO3 thick films prepared on YSZ and MgO substrates preferentially oriented along the a- and c-axes, respectively. The remanent polarization Pr of the MgO-based films was higher than that of the YSZ-based films (10.8 µC/cm2 vs 6.5 µC/cm2) and comparable to that of BaTiO3 bulk ceramics. Thermal expansion measurements of BaTiO3, YSZ, and MgO ceramics suggested that compressive stress was exerted on the BaTiO3 thick films, causing them to orient along the c-axis. (Ba0.92Ca0.08)(Ti0.975Zr0.025)O3 thick films were also prepared on the YSZ and MgO substrates and showed similar preference for the c-axis on MgO. However, the remanent polarization of (Ba0.92Ca0.08)(Ti0.975Zr0.025)O3 thick films prepared on MgO was greater than that of bulk ceramics (14.9 µC/cm2 vs 11.0 µC/cm2).

Electric properties of BaTiO3 lead-free textured piezoelectric thick film by screen printing method

(h00)-textured BaTiO3 thick film was fabricated on Pt substrate by screen printing method. Effects of template content on grain orientation and electric properties of the thick film were investigated. Grain orientation degree of thick film was optimized to 81 % with 20 % template content. Saturate polarization and coercive field of the textured thick film were 7.5μC/cm2 and 2.9 kV/cm, respectively. A diffusion behavior was observed by the temperature dependence of dielectric constant of BaTiO3 thick films. Piezoelectric properties of the thick film were characterized by relationship of unipolar strain and applied electric field. Piezoelectric constant d 33 * of grain orientation thick film was 136 pm/V, which was higher than that of non-textured film (d 33 * = 92 pm/V).

Interfacial Magnetoelectric Switching in Multiferroic Heterostructures

Novel methods of switching magnetism with electric fields and vice versa, and aiming at magnetoelectric (ME) data processing are reported. First, the patented MERAM@ uses the electric field control of exchange bias via an epitaxial Cr2O3 layer and exchange coupling to a Pt/Co/Pt trilayer. It promises to crucially reduce Joule energy losses in RAM devices. Second, magnetic switching of the electric polarization by a transverse magnetic field in a 3-1 composite of a vertically poled BaTiO3 thick film embedding CoFe2O4 nanopillars produces a regular surface polarization pattern with rectangular symmetry. Its possible use for data processing is discussed.

Physical properties of A(Cu1/3Nb2/3)O3 (A = Ba, Sr, Ca)-substituted BaTiO3 system grown by using aerosol deposition

The physical properties of the lead-free piezoelectric material BaTiO3 (BT) with complex perovskite phase additives, i.e., A(Cu1/3Nb2/3)O3 (A = Ba, Sr, Ca), were investigated. The dense and crack-free thick films with thickness of > 5 µm were grown on platinized Si(100) wafers by using the aerosol deposition method (AD) at room temperature. Compared to pure BT grown by using AD, complex perovskite-substituted BT thick films showed improved physical properties and film quality even after post annealing. The optimal amount of the additives and the optimal post annealing temperature were determined in accordance with the dielectric and the ferroelectric properties.