PbTiO3 Films Research Articles

Structure and Nanoscale Polarization Switching Induced by High Frequency Alternating Current in PbTiO<sub>3</sub> Polycrystalline Films

PbTiO3(PTO) films were successfully fabricated by sol-gel method. We studied the structure and the nanoscale polarization switching property using XRD and Piezoresponse Force Microscopy. The results reveal that the PTO films are single perovskite phase grain films with tetragonal structure, and are polycrystalline materials with no evidence of preferential orientation. The average grain size is about 150nm and a striped multi-domain structure is exhibited in individual grains. Under 15 kHz alternating current of PFM, a significant asymmetry of switching pattern was observed. We suggest that the cooperative action of the built-in electric field at the bottom interface and the PFM ac-voltage lead to the asymmetry switching.

Engineering 180° ferroelectric domains in epitaxial PbTiO3 thin films by varying the thickness of the underlying (La,Sr)MnO3 layer

Epitaxial ferroelectric thin films of PbTiO3 (PTO) grown on top of nominally La0.7Sr0.3MnO3 (LSMO) submicron hillocks on Nb-doped SrTiO3 (100) substrate were investigated by means of scanning transmission electron microscopy. 180° ferroelectric domains were observed in the c-axis oriented PTO films. The formation and configuration of ferroelectric domains and domain walls were found to exhibit strong correlation with the thickness of the underlying LSMO hillocks. The domain walls start at the locations of the hillocks where the LSMO layer has a thickness of about 3 nm. Our results demonstrate that controlling the thickness variation (shape) of the LSMO hillocks can manipulate the position and density of the ferroelectric domain walls, which are considered to be the active elements for future nanoelectronics.

Stress Modulation and Ferroelectric Properties of Nanograined PbTiO3 Thick Films on the Different Substrates Fabricated by Aerosol Deposition

Nanograined PbTiO3 (PT) thick films were deposited on Si, yttria‐stabilized zirconia (YSZ), and Ni substrates using an aerosol deposition (AD) method at room temperature. The AD PT thick films on each different substrate were annealed at 500°C and 700°C for 1 h to increase the crystallinity. The stresses in the PT film were modulated by controlling the difference in the coefficient of thermal expansion (CTE) between the films and substrates during the thermal annealing process. The morphology of the AD PT films was examined from the polycrystalline dense structure (thickness ~8 μm), and the changes in the crystallographic phase, in‐plane stresses, and ferroelectric properties in annealed films were investigated. In‐plane stress analysis showed that the PT films annealed at 500°C and 700°C on each substrate exhibited compressive stress. Owing to the effects of compressive stress in the PT film, the film showed less tetragonality (c/a ratio) and enhanced ferroelectric behaviors. The change in the polarization–electric field (P–E) hysteresis loop of the PT films was explained by the stress induced from CTE mismatch between the films and substrates.

Fe(III) doped and grafted PbTiO3 film photocathode with enhanced photoactivity for hydrogen production

The photoelectrochemical activity of the PbTiO3 film photocathode deposited on indium tin oxide-coated quartz substrate was significantly improved through modifying the film surface by both the Fe(III) doping and grafting. Doping the PbTiO3 with Fe(III) ions narrows its band gap thus increases the visible light utilization, while the surface-grafted Fe(III) ions on the doped PbTiO3 surface are helpful to improve the charge transfer on the photocathode/electrolyte interface. Consequently, the photocurrent was increased from 38 μA/cm2 to 220 μA/cm2 under the irradiation of 100 mW/cm2 Xe lamp by using 0.1M Na2SO4 as an electrolyte and zero-potential versus saturated calomel as a reference electrode. The corresponding increase in open circuit voltage was 0.95–1.11 V.

The potential role of amorphous lead titanate thin films as nanodielectric layer for capacitor applications

A Study of thin films preparation faces many challenges due to the environmentally sensitivity that could initiate effect towards device performance. Requirement to fabricate the passive device like capacitor at such nanoscaled thickness is quite challenges that would initiate the effect on the device performance. Nowadays, capacitor not just only existed by conventional dielectric material, it can become a complex device when ferroelectric materials get involved. This material promotes useful knowledge of their polarization behavior which contains switching element that premier contribution for memory storage applications. The present study demonstrates the potential of amorphous PbTiO3 thin films as nanodielectric layer for high performance capacitor at low voltage applications. This unique characteristic of amorphous structure performs such incredible high dielectric constant value about ~100 and tangent loss of 4-5%, measured at 1 kHz. The PbTiO3 films also involve other electrical measurement like P-E hysteresis loop.

Impact of thermal stress on the piezoelectric and dielectric properties of PbTiO3 thick films on various substrates

The impact of thermal stress on the polarization, as well as dielectric and piezoelectric properties of (001) oriented PbTiO3 (PTO) thick films deposited on various substrates was investigated based on Landau-Devonshire thermodynamic model. The results showed that dielectric and piezoelectric properties of PTO films depend strongly on the thermal stress in PTO films decided by the deposition temperature TG and the thermal expansion coefficients' difference between PTO films and substrates. For IC-compatible substrates such as Si, c-sapphire, and a-sapphire that induce tensile in-plane thermal stresses, the dielectric and piezoelectric responses and tunabilities of PTO films were enhanced. Whereas for PTO films on MgO, compressive thermal in-plane stresses can degraded the dielectric and piezoelectric responses and tunabilities of the films.

Upshift of phase transition temperature in nanostructured PbTiO3 thick film for high temperature applications.

Thick polycrystalline pure PbTiO3 films with nano size grains were synthesized for the first time by aerosol deposition. Annealed 7 μm thick films exhibit well-saturated ferroelectric hysteresis loops with a remanent polarization and coercive field of 35 μC/cm(2) and 94 kV/cm, respectively. A large-signal effective d33,eff value of >60 pm/V is achieved at room temperature. The measured ferroelectric transition temperature (Tc) of the films ∼550 °C is >50 °C higher than the reported values (∼490 °C) for PbTiO3 ceramics. First-principles calculations combined with electron energy loss spectroscopy (EELS) and structural analysis indicate that the film is composed of nano size grains with slightly decreased tetragonality. There is no severe off-stoichiometry, but a high compressive in-plane residual stress was observed in the film along with a high transition temperature and piezoelectric response. The ferroelectric characteristics were sustained until 200 °C, providing significant advancement toward realizing high temperature piezoelectric materials.

The effects of strain relaxation on the dielectric properties of epitaxial ferroelectric Pb(Zr0.2Ti0.8)TiO3 thin films

We study the effects of strain relaxation on the dielectric properties of epitaxial 40 nm Pb(Zr0.2Ti0.8)TiO3 (PZT) films. A significant increase in the defect and dislocation density due to strain relaxation is observed in PZT films with tetragonality c/a < 1.07 grown on SrTiO3 (001) substrates, which results in significant frequency dispersion of the dielectric constant and strong Rayleigh type behavior in those samples. This combined structural-electrical study provides a framework for investigating strain relaxation in thin films and can provide useful insights into the mechanisms of fatigue in ferroelectric materials.

Bi(Ni1/2Zr1/2)O3-PbTiO3 relaxor-ferroelectric films for piezoelectric energy harvesting and electrostatic storage

In this Letter, we demonstrated that both a high energy-storage density and a large piezoelectric response can be attained simultaneously in relaxor-ferroelectric 0.4Bi(Ni1/2Zr1/2)O3-0.6PbTiO3 films prepared by chemical solution deposition. The as-prepared films had a pure-phase perovskite structure with an excellent crystalline morphology, featuring a moderate relative permittivity (εr ∼ 800–1100), a low dissipation factor (tan δ < 5%) and strong relaxor-like behavior (γ = 1.81). An ultra-high energy-storage density of 39.8 J/cm3 at 2167 kV/cm was achieved at room temperature. Moreover, the 0.4Bi(Ni1/2Zr1/2)O3-0.6PbTiO3 films exhibited a considerably large effective piezoelectric coefficient of 83.1 pm/V under substrate clamping, which is comparable to the values obtained for lead zirconate titanate films. Good thermal stabilities in both the energy-storage performance and the piezoelectric properties were obtained over a wide range of temperatures, which makes 0.4Bi(Ni1/2Zr1/2)O3-0.6PbTiO3 films a promising candidate for high energy-storage embedded capacitors, piezoelectric micro-devices, and specifically for potential applications in next-generation integrated multifunctional piezoelectric energy harvesting and electrostatic storage systems.

In-situ Raman Spectroscopic Investigation of the Effect of Cooling Speed on Domain Formation in PbTiO3 Films

The influence of the post-deposition cooling speed on the domain formation process of PbTiO3 films was investigated using MOCVD equipment combined with in-situ Raman spectroscopy. The accumulation and relaxation of strain during the post-deposition cooling process is responsible for the domain structure. The Curie temperature for fast cooling is lower than that for slow cooling. Additionally, the residual strain with fast cooling is smaller than that with slow cooling. These observations suggest that the volume fraction of the c-domain is larger for fast cooling and that the atmospheric conditions during the first post-deposition cooling process may control the domain structure.

Gamma-ray irradiation effects on electrical properties of ferroelectric PbTiO3 and Pb(Zr0.52Ti0.48)O3 thin films

We investigated gamma-ray irradiation effects on electrical properties of ferroelectric PbTiO3 (PTO) and Pb(Zr0.52Ti0.48)O3 (PZT) thin films. PTO and PZT thin films were prepared on the Pt/Ti/SiO2/Si substrates by using a sol–gel method with a spin-coating process. The prepared PTO and PZT thin films were subjected to gamma radiation with various total doses from 0kGy to 300kGy. There were no noticeable morphological and structural changes in PTO and PZT films before and after irradiation. As a total dose increases up to 300kGy, a larger degradation behavior of electrical properties was observed in the PZT films rather than in the PTO films. About 35% of remanent polarization value decreased for the PZT films, while just 10% of that decreased for the PTO films. Dielectric constant of PZT films decreased much from 850 to 580, but that of the PTO films decreased just a little from 400 to 340. This degradation behavior of polarization and dielectric properties can be explained by the pinning of domain walls by some radiation-induced defects. These results suggest that the PTO films have higher radiation hardness properties than the PZT films.

Interfacial charge and strain effects on the ferroelectric behavior of epitaxial (001) PbTiO3 films on (110) DyScO3 substrates

In-situ synchrotron x-ray observations reveal that the ferroelectric behavior of epitaxial (001) PbTiO3 thin films grown on (110) DyScO3 substrates depends on both film thickness and interfacial electrical properties. A 92-nm-thick film was found to exhibit an a/c domain structure with a ferroelectric Curie temperature similar to that theoretically predicted based on the strain state. In contrast, 6-nm-thick films contained only c-oriented domains, and the ferroelectric behavior was found to depend strongly on the nature of the electrical boundary condition at the buried interface.

Atomic-scale mapping of dipole frustration at 90° charged domain walls in ferroelectric PbTiO3 films.

The atomic-scale structural and electric parameters of the 90° domain-walls in tetragonal ferroelectrics are of technological importance for exploring the ferroelectric switching behaviors and various domain-wall-related novel functions. We have grown epitaxial PbTiO3/SrTiO3 multilayer films in which the electric dipoles at 90° domain-walls of ferroelectric PbTiO3 are characterized by means of aberration-corrected scanning transmission electron microscopy. Besides the well-accepted head-to-tail 90° uncharged domain-walls, we have identified not only head-to-head positively charged but also tail-to-tail negatively charged domain-walls. The widths, polarization distributions, and strains across these charged domain-walls are mapped quantitatively at atomic scale, where remarkable difference between these domain-walls is presented. This study is expected to provide fundamental information for understanding numerous novel domain-wall phenomena in ferroelectrics.

Tailoring properties of ferroelectric ultrathin films by partial charge compensation

Partial charge compensation in ferroelectric nanostructures is known to play a critical role in stabilizing equilibrium domain patterns. We use first-principles-based simulations to study the effect of partial charge compensation on the response of polarization to the electric field in PbTiO3 and BaTiO3 ultrathin films. Computational data predict that the response can be altered at the qualitative level by tailoring partial charge compensation. We report an unusual transition from ferroelectric to antiferroelectric to dielectric behavior induced by the change in the amount of compensating charge. Interestingly, films with antiferroelectric features exhibit superior potential for energy storage applications.

Síntese e caracterização de pós e filmes de titanato de chumbo obtidos através do método Pechini

The lead titanate, PbTiO3 (PT), is a material in its amorphous phase has photoluminescent properties, dielectric, piezoelectric and electromechanical and ferroelectric properties, which give the PT various applications. In this work PT powders and films were obtained and the influence of pH and heat treatment of sols were investigated in order to minimize the appearance of a secondary phase in the amorphous phase of PT. The PT powders were characterized via thermal analysis, infrared spectroscopy, X-ray diffraction, while the PT films were characterized by diffraction of x-rays by scanning electron microscopy. The thermal analysis of powders PT suggested the beginning of its crystallization temperature of 600o C, confirmed by measurements of XRD which indicated to obtain the disordered phase of PbTiO3 at annealing temperature of 400° C starting from the resin precursor pH 2 and 10. The analyzes in the film PT to indicate that certain factors should be considered for films to have the expected properties such as pH, heat treatment time and the number of deposited layers.

Microstructure development of BiFeO3–PbTiO3 films deposited by pulsed laser deposition on platinum substrates

BiFeO3–PbTiO3 films around the morphotropic phase boundary were deposited by pulsed laser deposition on polycrystalline Pt/TiOx/SiO2/Si substrates. X-ray analysis confirms that 0.6BiFeO3–0.4PbTiO3 films are (001) tetragonal preferentially orientated due to lattice matching with the underlying substrate. The misfit strain at the substrate–film interface is relieved by a ∼19% orientation transformation from (001) to (100) due to the lattice mismatch at the substrate–film interface and the difference in thermal expansion coefficients of the substrate and deposited film. 0.7BiFeO3–0.3PbTiO3 films are mixed-phase rhombohedral-tetragonal with (001)/(111) preferential orientation due to the lattice match to the (111) and (100) of the underlying platinum as well as to being close to the morphotropic phase boundary. Inconsistent structural and electrical properties in reported BiFeO3–PbTiO3 films are explained in terms of film morphology and diffusion of bismuth into platinum. Films below ∼220nm thickness produce short circuits due to a Volmer–Weber growth mechanism which results in physical defects within the films. Films above this critical thickness also produce variable electrical properties due to diffusion of bismuth into the underlying platinum electrode which has been confirmed by energy dispersive X-ray spectroscopy.

Ferroelectric property of a hydrothermally-grown PbTiO3 film with an aerosol-deposited seed layer

The hydrothermal method is a unique method for the growth of ferroelectric materials because their materials can be grown at a relatively low reaction temperature below 250 °C. To grow a PbTiO3 (PT) film on a metal Ni substrate, we first deposited a PT seed layer on the Ni substrate by using the aerosol deposition (AD) method; then we grew PT film on top of the PT seed layer by using the hydrothermal process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that the AD PT film acted well as a seed layer and that a highly-dense PT film had been successfully grown following the crystal structure of the seed layer. Both the PT seed layer and the hydrothermally-grown PT film had distorted crystal structures with decreased tetragonality. The output voltage due to impact on the film confirmed that the hydrothermally-grown PT film had a spontaneous polarization along the ‘c’ axis. The hydrothermally-grown PT film exhibited ferroelectric hysteresis loops without mechanical breakage during several cyclic measurements.

Influence of the interfacing with an electrically inhomogeneous bottom electrode on the ferroelectric properties of epitaxial PbTiO3

The influence of an electrically inhomogeneous epitaxial bottom layer on the ferroelectric and electrical properties has been explored in epitaxial PbTiO3 (PTO)/La0.7Sr0.3MnO3 (LSMO) submicron structures using atomic force microscopy. The submicron LSMO-dot structures underneath the ferroelectric PTO film allow exploring gradual changes in material properties. The LSMO interfacial layer influences significantly both electrical and ferroelectric properties of the upper PTO layer. The obtained results show that the as-grown polarization state of an epitaxial ferroelectric layer is strongly influenced by the properties of the layer on top of which it is deposited.

Thickness scaling of ferroelastic domains in PbTiO3 films on DyScO3

We report on the thickness dependence of the ferroelastic domains of PbTiO3 films grown on (110)-DyScO3 with low thicknesses (up to 240 nm), which fall outside the validity range of the square root law proposed by Roytburd. For slow-grown films, the data reveal the linear thickness dependence predicted by Pertsev and Zembilgotov, using a complete elastic description, while a 2/3 scaling exponent is found for fast-grown films. Extremely long domains running all through the samples have been observed in the latter case, compared to the short domains observed in slow-grown films. These differences are ascribed to the in-plane anisotropy for domain wall nucleation, which is likely caused by the anisotropic elastic modulus of the substrate.

Characterization of Nanomechanical, Ferroelectric, and Piezoelectric Properties by Nanoindentation and Piezoresponse Force Microscopy of PbTiO3 Thin Films

Lead titanate PbTiO3 films were deposited onto Pt(111)/Ti/SiO2/Si(100) substrates by the aerosol assisted chemical vapor deposition (AA-CVD) process followed by thermal annealing at 550 °C for 12 h. Piezoresponse force microscopic observations revealed a nano laminar domain structure in the PbTiO3 grains, and we attribute the lamellar domains to 180 and 90° ferroelectric domains. The polarization-switching mechanism of the domains in the representative PbTiO3 film under an external electric fields has also been studied, and it was revealed that a large-area polarization switching is usually accompanied by the appearance of a new direction of 90° domains in order to reduce the stress in the grains. Finally, nanomechanical properties such as the elastic modulus and hardness were evaluated by nanoindentation using the continuous stiffness measurement technique.