Microstructure,ferroelectric and piezoelectric properties of Bi4Ti3O12 platelet incorporated 0.36BiScO3-0.64PbTiO3 thick films for high temperature piezoelectric device applications

Bi₄Ti₃O₁₂ (BiT) platelet incorporated 0.36BiScO₃-0.64PbTiO₃ (BS-PT) thick films were successfully developed for high temperature piezoelectric device applications. Their microstructure and ferroelectric and piezoelectric properties were systematically investigated to demonstrate the effect of the BiT template. It was found that the incorporation of BiT template was not responsible for textured grain growth of the BS-PT thick films; however, it could result in grain growth and densification of the BS-PT thick films by optimizing the sintering temperature and amount of BiT template. In particular, a 4 wt% BiT-incorporated BS-PT thick film sintered at 1000°C exhibited a pure perovskite structure and excellent piezoelectric properties of d₃₃ (440 pC/N) and k_p (53%), despite the presence of micro-pores caused by molten BiT. The BS-PT thick film, exhibiting good ferroelectric characteristics of P_r of 39.4 μC/cm² and E_c of 3.0 kV/mm at 1 kHz, also had an extremely high T_c of approximately 402°C. This implies that the BiT platelet incorporated BS-PT thick film is applicable for high temperature piezoelectric devices.     

Structural and electrical properties of Na0.5Bi4.0RE0.5Ti4O15 (RE=Tm,Yb and Lu) thin films

In the current study, a series of lanthanide ions, Tm, Yb and Lu, were used for doping at the Bi-site of the Aurivillius phase Na_0.5Bi_4.5Ti₄O₁₅ (NaBTi) to investigate the structural, electrical and ferroelectric properties of the thin films. In this regard, Na_0.5Bi_4.5Ti₄O₁₅ and the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5i₄O₁₅ (RE=Tm, Yb and Lu, denoted by NaBTmTi, NaBYbTi, and NaBLuTi, respectively) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of the Aurivillius phase orthorhombic structures for all the thin films were confirmed by X-ray diffraction and Raman spectroscopic studies. Based on the experimental results, the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5Ti₄O₁₅ thin films exhibited a low leakage current and the improved ferroelectric properties. Among the thin films, the NaBLuTi thin film exhibited a low leakage current density of 6.96×10⁻⁷ A/cm² at an applied electric field of 100 kV/cm and a large remnant polarization (2P_r) of 26.7 μC/cm² at an applied electric field of 475 kV/cm.     

Dielectric and ferroelectric properties of Ta-modified Bi3.25La0.75Ti3O12 ceramics

B-site modified Bi_3.25La_0.75Ti_3-xTa_xO₁₂ ceramics were prepared by the conventional solid-state reaction method. The influence of Ta₂O₅ on microstructure and electric properties of the ceramics was investigated. The results demonstrated that Ta⁵⁺ ions were dissolved into the perovskite lattice and homogeneously distributed in the matrix without forming any minority phase. The conduction mechanism and dielectric response behavior were transformed with Ta substation, which is triggered by varied structural distortion characteristics and defect diploes. The Curie temperature decreased gradually with increasing Ta content and a relaxor-like behavior was observed for x = 0.09 sample. The internal bias field is decreased with Ta doping, because the substitution of Ta⁵⁺ at B-site contributes to release the involved oxygen vacancies in defect diploes. Moreover, further increasing Ta content causes a reduction in the oxygen vacancies located at lattice misfits, resulting in a decrease of coercive fields. An improved ferroelectric properties were obtained for x = 0.09 sample with a relatively lower coercive field and a larger spontaneous polarization.     

Pyrochlore structure and dielectric properties of bismuth zinc niobate thin films prepared by RF sputtering

Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films with thickness from 60 nm to 200 nm were prepared by radio-frequency magnetron sputtering and post-annealed from 550 °C to 650 °C. The x-ray diffraction results indicated that the BZN thin films possessed a cubic pyrochlore phase. The BZN thin films exhibited thickness-independent dielectric properties with dielectric constant of ~180 and low loss tangent less than 1% at 10 kHz as the film thickness decreased to 60 nm. The BZN thin films with thickness of 200 nm and post-annealed at 650 °C had a tunability of 32.7% at a DC bias field of 1.5 MV/cm. The results suggest that the BZN thin films have promising applications on the embedded capacitors, tunable devices and energy storage devices.     

Microstructure and ferroelectric properties of Ta-doped Bi3.25La0.75Ti3O12/ZnO thin film capacitors

Ta-doped Bi_3.25La_0.75Ti₃O₁₂(BLTT)/ZnO films were fabricated on Pt(111)/Ti/SiO₂/Si substrates by a magnetron sputtering method. Firstly, ZnO crystal thin films were grown on the substrates by a reactive sputtering method. Then, BLTT thin films were deposited on the ZnO layers at room temperature and post-annealed at 600 °C. The micromorphology, ferroelectric and dielectric properties of BLTT/ZnO films were analyzed. The XRD analysis shows that ZnO buffer layer significantly reduces the crystallization temperature of BLTT thin film. The TEM results show that lamellar BLTT grains are grown on ZnO layer at a certain angle with few elements diffusion at the interface of ZnO phase and Bi₄Ti₃O₁₂ phase. The ferroelectric properties indicate that BLTT/ZnO films exhibit different remanent polarization and coercive fields under electric field with different directions. The novel mechanism of tailoring ferroelectric properties may open new possibilities for designing special ferroelectric devices.     

Enhanced pyroelectric and piezoelectric responses in W/Mn-codoped Bi4Ti3O12 Aurivillius ceramics

The pyroelectric and piezoelectric properties of 4 at% Mn-doped Bi₄Ti_2.9W_0.1O₁₂ (BiTW-Mn) Aurivillius ceramic were investigated and compared to Bi₄Ti_2.9W_0.1O₁₂ (BiTW) counterpart, which were fabricated using a conventional solid state reaction method. High resistivities of 4.9?×?10¹² and 2.5?×?10¹¹ Ω?cm at 100?°C were obtained in the W-doped and W/Mn-codoped BiT ceramics, respectively. They showed similar activation energies and ionic-p-type mixed conduction mechanisms. Higher pyroelectric coefficients of 57.1?μC/m²K and piezoelectric coefficients of 21 pC/N, as well as much lower dielectric loss of 0.003 were achieved in W/Mn-codoped ceramics. These property changes were mainly induced by $\text{M}{\text{n}}_{\text{Ti}}^{}?{\text{V}}_{\text{o}}^{}$ defect dipoles. The effect of acceptor doping was evidenced by an internal bias field, shown by a horizontal offset in the polarization-field behavior. The improved properties together with high thermal stability indicate that BiTW-Mn may be a promising candidate for pyroelectric and piezoelectric devices at elevated temperatures.     

Temperature dependence of electrical and electromechanical properties of Pb(Mg1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 thin films

The electrical and electromechanical properties of Pb(Mg_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ (PMN–PNN–PZT, PMN/PNN/PZT = 20/10/70) on Pt/Ti/SiO₂/Si substrates by chemical solution deposition was investigated. The PMN–PNN–PZT films annealed at 650 °C exhibited slim polarization hysteresis curves and a high dielectric constant of 2100 at room temperature. A broad dielectric maximum at approximately 140–170 °C was observed. The field-induced displacement was measured by scanning probe microscopy, the bipolar displacement was not hysteretic, and the effective piezoelectric coefficient (d₃₃) was 66 × 10⁻¹² m/V. The effective d₃₃ decreased with temperature, but the value at 100 °C remained 45 × 10⁻¹² m/V.     

Fabrication of CaLa4(Zr0.05Ti0.95)4O15 thin films by RF magnetron sputtering

Crystalline CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films deposited on n-type Si substrates byRF magnetron sputtering at a fixed RF power of 100 W, an Ar/O₂ ratio of 100/0, an operating pressure of 3 mTorr, and different substrate temperatures were investigated. The surface structural and morphological characteristics analyzed by X-ray diffraction and atomic force microscopy were sensitive to the deposition conditions, such as the substrate temperature. The diffraction pattern showed that the deposited films had a polycrystalline microstructure. As the substrate temperature increased, the quality of the CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films improved, and the kinetic energies of the sputtered atoms increased, resulting in a structural improvement of the deposited CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films. A high dielectric constant of 16.7 (f=1 MHz), a dissipation factor of 0.19 (f=1 MHz), and a low leakage current density of 3.18×10⁻⁷ A/cm² at an electrical field of 50 kV/cm were obtained for the prepared films.     

Structural and electrical properties of La3+-doped Na0.5Bi4.5Ti4O15-Bi4Ti3O12 inter-growth high temperature piezoceramics

New lead-free inter-growth piezoelectric ceramics, Na_0.5Bi_8.5-xLa_xTi₇O₂₇ (NBT-BIT-xLa, 0.00≤x≤1.00), were prepared by the conventional solid-state method. Structural and electrical properties of NBT-BIT-xLa were studied. All the NBT-BIT-xLa samples exhibited a single inter-growth structured phase. XRD and Raman spectroscopy revealed a reduced orthorhombicity, which strongly supports the variation of dielectric and ferroelectric properties. Plate-like grains were found to decrease with the increasing x contents. Impedance spectra analysis indicated that oxygen vacancy defects dominated the contributions to the electrical conductivity. The increased activation energies for dc conductivity evidenced the reduction of oxygen vacancy concentration after La substitution, inducing the enhancement in piezoelectric constant (d₃₃) and remanent polarization (2P_r). The studies of thermal depoling indicated that the optimal d₃₃ of NBT-BIT-0.50La ceramics still remained 22 pC/N at 500 °C, implying that this ceramics could be potentially applied into high temperature devices.     

Preparation of ferroelectric Pb(Zr0.52 Ti0.48)O3 thin films by sol-gel processing

Ferroelectric Pb(Zr_0.52 Ti_0.48)O₃ thin films were prepared by sol-gel processing on the Pt/Ti/SiO₂/Si(100) substrates. Effects of the concentration (0.2–0.8 M) of the starting solution (Pb/Zr/Ti= 1.1/0.52/0.48) and the sintering temperature (500–700 ‡C) on crystallinity, microstructure and electrical properties of PZT thin films were investigated. For the thin film prepared at 0.4 M starting solution, the highest crystallinity appeared at a sintering temperature of 650 ‡C. The average grain size of the PZT thin films was about 0.17 Μm. The film thickness was about 0.2 Μm. The relative dielectric constant and the dissipation factor of the film measured at 1 kHz were about 750 and 4.3%, respectively. The remnant polarization (Pr) and coercive field (Ec) of the film measured at the applied voltage of 5 V were about 49 ΜC/cm² and 134 kV/cm, respectively.     

The effect of the annealing atmosphere on the properties of Sr2Bi4Ti5O18 ferroelectric thin films

The Sr₂Bi₄Ti₅O₁₈ (SBT-5) ferroelectric thin films were prepared on Pt/Ti/SiO₂/Si substrate using the sol-gel method and annealing in oxygen, air, and nitrogen. Their properties were measured. After annealing in oxygen, the films showed good crystallization and a larger average grain size of approximately 34.05 nm. XPS analysis clearly showed that annealing in oxygen inhibited the generation of oxygen vacancies in the films, which contributed to the melioration of the ferroelectric properties. The remanent polarization was 20.09 μC/cm² and the coercive field was 75 kV/cm. When the electric field was 15 kV/cm, the leakage current density was approximately 3.88 × 10⁻⁷A/cm², while the Ohmic conduction was the dominating leakage mechanism. Because the content of the oxygen vacancy in the samples annealed in oxygen atmosphere was lower, the fixing effect on the domain structure was weaker and the volume effect was not obvious, so the aging degree of the samples was low. The larger relative dielectric constant was 742, while the dielectric loss was 0.037 when the test frequency was 2.0 × 10⁵ Hz.     

Enhancing the thermal stability of switched domains in lithium niobate single-crystal thin films

Lithium niobate on insulator (LNOI) is widely used in optical, acoustic, domain wall current (DWC)-based integrated circuits and other domain engineering devices, enabling higher material performance, higher domain integration density and more advanced applications. However, there are hidden dangers of thermal failure in these highly integrated domain engineering devices. Therefore, maintaining thermal stability of domain structures in ferroelectric single-crystal thin films is an important and challenging task. Here, thermally induced structure reconstruction of tailored metastable switched domains was research in a 500 nm thick congruent lithium niobate (CLN) thin film, and a method for enhancing the thermal stability of switched domains was proposed. Piezoresponse force microscopy (PFM) and a polyheater are used to accurately monitor the thermal evolution of switched domains in CLN thin film sample. The results indicate the switched domain structures determine the thermal stability, and the enhanced thermal stability of the switched domains increases from 55 to 85 °C–150 °C. In this contribution, the thermal failure in domain engineering devices can be avoided effectively. The investigation paves the way for the development of domain engineering devices based on lithium niobate (LN) thin films.     

Fabrication and characterization of intergrown Bi4Ti3O12-based thin films using a metal-organic precursor solution

Ferroelectric intergrowth-structured Bi₄Ti₃O₁₂-based thin films have been fabricated by chemical solution deposition. Bi₄Ti₃O₁₂–SrBi₄Ti₄O₁₅ (BiT–SBTi) and SrBi₂Nb₂O₉–Bi₄Ti₃O₁₂ (SBN–BiT) precursor films crystallized in the desired intergrown BiT–SBTi and SBN–BiT structures on Pt/TiO_x/SiO₂/Si substrates by optimizing the processing conditions. Synthesized BiT–SBTi and SBN–BiT thin films exhibited ferroelectric P–E hysteresis loops. The BiT–SBTi thin films crystallized at 750 °C showed a 2P_r value approximately 20 μC/cm². Although a little smaller P_r value was observed for the SBN–BiT thin films, the squareness of a P–E hysteresis loop was superior to that of BiT–SBTi thin films. Also, the SBN–BiT thin films had a smoother surface morphology compared with BiT–SBTi thin films.     

Dielectric and magnetic studies of 0.5Bi2/3Cu3Ti4O12 - 0.5Bi3LaTi3O12 nano-composite ceramic synthesized by semi-wet route

A nano-composite electro ceramic with the chemical composition of 0.5Bi_2/3Cu₃Ti₄O₁₂ - 0.5Bi₃LaTi₃O₁₂ was synthesized by a semi-wet route using high purity metal nitrate and solid TiO₂ in a stoichiometric ratio. X-ray diffraction (XRD) analysis showed the presence of Bi₃LaTi₃O₁₂ (BLTO) and Bi_2/3Cu₃Ti₄O₁₂ (BCTO) phases in the composites sintered at 900 °C for 8 h. Transmission electron microscope (TEM) analysis of the composite shows the presence of nanoparticles in the range of 55±3 nm. Atomic force microscopy (AFM) study also substantiates the presence of nanoparticles in the composite. Scanning electron microscope (SEM) images show that the surface morphology consists of plates like and spherical grains. The study of PE hysteresis loop revealed no saturation polarization which suggested lossy capacitor behavior of the composite. Magnetic behavior of the composite shows the weak ferromagnetic nature in M-T and M-H curve. The High observed value of dielectric constant (ε’=13.94×10³) of the composite may be due to the presence of space charge polarization.     

Electronic structure and transport properties of sol-gel-derived high-entropy Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 thin films

High-entropy perovskite thin films, as the prototypical representative of the high-entropy oxides with novel electrical and magnetic features, have recently attracted great attention. Here, we reported the electronic structure and charge transport properties of sol-gel-derived high-entropy Ba(Zr_0.2Sn_0.2Ti_0.2Hf_0.2Nb_0.2)O₃ thin films annealed at various temperatures. By means of X-ray photoelectron spectroscopy and absorption spectrum, it is found that the conduction-band-minimum shifts downward and the valence-band-maximum shifts upward with the increase of annealing temperature, leading to the narrowed band gap. Electrical resistance measurements confirmed a semiconductor-like behavior for all the thin films. Two charge transport mechanisms, i.e., the thermally-activated transport mechanism at high temperatures and the activation-less transport mechanism at low temperatures, are identified by a self-consistent analysis method. These findings provide a critical insight into the electronic band structure and charge transport behavior of Ba(Zr_0.2Sn_0.2Ti_0.2Hf_0.2Nb_0.2)O₃, validating it as a compelling high-entropy oxide material for future electronic/energy-related technologies.     

Selective formation of crystal polymorphs in Er3+-doped Bi2O3 thin films and their photoluminescence properties

The process conditions for selectively forming crystal polymorphs in Er³⁺-doped Bi₂O₃ films deposited on Si, SiO₂, and C-plane sapphire substrates were systematically investigated. Bi₂O₃:Er films were deposited at either room temperature or 300 °C and subsequently post annealed to promote crystallization. The critical factor controlling the crystal polymorphs was Er content. When the Er content was less than 1.5 at.%, only α-Bi₂O₃ phase nucleated upon post annealing. Deposition at 300 °C somewhat lowered the oxidization state, under which β-Bi₂O₃ structure appeared at lower temperatures and α-Bi₂O₃ structure appeared at higher temperatures. When the films were doped with over 2 at.% Er³⁺ ions, the excess Er₂O₃ stabilized the δ-Bi₂O₃ structure as the lowest temperature phase. The universal phase transition scheme with increasing annealing temperature was δ-Bi₂O₃ → β-Bi₂O₃ → α-Bi₂O₃. The δ → β transition proceeded through splitting each diffraction peak of δ-Bi₂O₃ into two components of β-Bi₂O₃, indicating a correlation between the structures of β-Bi₂O₃ and δ-Bi₂O₃. The γ-Bi₂O₃ phase appeared only in films on Si(100) substrates and after vacuum annealing, suggesting the formation of sillenite (Bi₁₂SiO₂₀). Deposition on C-plane sapphire by using H₂O as the oxygen source gas produced a highly (111)-oriented δ-Bi₂O₃ structure, whereas deposition with O₂ yielded a randomly oriented δ-Bi₂O₃ structure. At Er content exceeding 4 at.%, δ-Bi₂O₃ was the primary phase in the films on SiO₂. The photoluminescence (PL) activity of dopant Er³⁺ under excitation at a wavelength of 532 nm strongly depended on the crystal polymorphs. α-Bi₂O₃:Er exhibited intense and stable PL spectra consisting of eight Stark splitting lines. PL from γ-Bi₂O₃:Er exhibited much weaker two emission lines. δ-Bi₂O₃:Er and β-Bi₂O₃:Er films were not emission-active at all. However, δ-Bi₂O₃:Er film on SiO₂ with an Er content of 4 at.% exhibited an intense and broad emission at 1530 and 1560 nm.     

Effects of LiF addition on microstructure and dielectric properties of CaCu3Ti4O12 ceramics

The effects of small amounts of lithium fluoride sintering aid on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics were investigated. CCTO polycrystalline ceramics with 0.5 and 1.0 mol% LiF, and without additive were prepared by solid state synthesis. Good densification (>90% of the theoretical density) was obtained for all prepared materials. Specimens without the sintering aid and sintered at 1090 °C exhibit secondary phases as an outcome of the decomposition reaction. The mean grain size is controlled by the amount of LiF in specimens containing the additive. Impedance spectroscopy measurements on CaCu₃Ti₄O₁₂ ceramics evidence the electrically heterogeneous nature of this material consisting of semiconductor grains along with insulating grain boundaries. The activation energy for grain boundary conduction is lower for specimens prepared with the additive, and the electric permittivity reached 53,000 for 0.5 mol% LiF containing CCTO.     

Band structure and thermoelectric properties of inkjet printed ZnO and ZnFe2O4 thin films

The band structure and thermoelectric properties of inkjet printed ZnO and ZnFe₂O₄ thin films have been investigated. The bulk pellets were prepared by a solid-state method and thin films were deposited using an inkjet printing method. Multiple print cycles were required to fabricate homogeneous films and the composition of the thin films can be varied by varying the relative amounts of liquid deposited. It was possible to obtain high thermoelectric properties of ZnO by controlling the ratios of dopant added and the temperature of the heat treatments. XRD analysis showed that the fabricated samples have a wurtzite structure and an additional ZnAl₂O₄ phase was formed with increasing Al content and sintering temperature. It was found that the band gap of Al doped ZnO becomes smaller with increasing Al content and thus the electrical conductivity of Al_x doped ZnO (x=0.04) thin films showed the highest electrical conductivity (114.10 S/cm). The ZnFe₂O₄ samples were compared against the ZnO samples. The formation of single phase cubic spinel structure of the sintered ZnFe₂O₄ samples was found and confirmed by X-ray diffraction technique. Secondary phase Fe₂O₃ was also detected for compositions with Zn (x≤0.4). Finally, we want to report that the electrical conductivity of Zn_xFe_3−xO₄ was lower than the conductivity of the Al-doped ZnO.     

Influence of secondary phases on ferroelectric properties of Bi0.5Na0.5TiO3 ceramics

The effects of secondary phases on ferroelectric properties of Bi_0.5Na_0.5TiO₃ (BNT) have been studied. Ceramic powders were prepared by solid state reaction employing different sintering temperatures and characterized by X-ray diffraction (XRD), Scanning Electron Microscopy and impedance spectroscopy. The perovskite structure was detected by XRD; together with small peaks corresponding to a secondary phase assigned to the Na₂Ti₆O₁₃-based phase in calcined powders. In addition, morphology and the content of the secondary phase were modified by the sintering temperatures, affecting the ferroelectric properties, and ac and dc conductivities. We believe that our results can benefit not only the understanding of BNT ceramics, but also expand the range of applications.