Antiferroelectric PbZrO3 Thin Films Research Articles

The differences in phase transition characteristics of antiferroelectric PbZrO3 thin films via grain size engineering

PbZrO3 (PZO) possesses a unique antiferroelectric-ferroelectric (AFE-FE) phase transition under an external electric field and engages more attention in understanding and regulating the phase transition behavior. In this work, changing annealing temperature (600–750 °C) and ultralow content (5‰) ions doping are used to optimize the phase transition of PZO films via grain size engineering. As annealing temperature increases, the maximum polarization Pmax increases but forward/backward switching fields EF/EA reduce accompanied by the average grain size enhances from 622 to 686 nm. Following, 5‰ mol aliovalent ion La3+ or K+ doped PZO-650 films both enhance Pmax and EF/EA indicating the strengthened antiferroelectricity, and meanwhile the grain size enhances to ∼800 nm. A high discharge density of 31 J/cm3 is achieved for 5‰ mol La-doped PZO films at a low electric field of 1 MV/cm, which is ∼100 % higher than those of pure PZO films at different annealing temperatures. This work compares the phase transition characteristics changes in PZO films by changing annealing temperature and ultra-low content ion doping strategy, which would provide new thinking in grain size-engineered antiferroelectric materials for energy storage applications.

High energy storage of PbZrO3 antiferroelectric thin films via constructing phase composition

In this paper, we fabricated PbZrO3 (PZ) thin films by the way of sol–gel spin on LaNiO3 buffered SiO2/Si substrates, and annealed them at different given temperatures by rapid thermal annealing (RTA). By controlling annealing temperature, PZ thin films showed different microstructures and phase compositions, whose impact of electrical properties and energy storage performance were researched. According to the research findings, the phase composition of film presents a general rule with the decrease of annealing temperature: PZ thin films crystallize into perovskite phase, pyrochlore phase, and amorphous phase. The films annealed at 620 °C crystallized into a state of coexistence of pyrochlore phase and perovskite phases, which also show moderate recoverable energy density and the highest energy storage efficiency (8.7 J cm−3 and 93.1%). This energy storage performance can be attributed to the synergistic effect of high electric breakdown strength of dense pyrochlore phase structure and high maximum polarization of perovskite phase. The findings of this paper help to explain the influence of pyrochlore phase on the energy storge performance of thin films. Thus, it is useful way to improve the energy storage performance of thin films.

Phase Competition in High-Quality Epitaxial Antiferroelectric PbZrO3 Thin Films.

Antiferroelectric PbZrO3 has attracted renewed interest in recent years because of its unique properties and wide range of potential applications. However, the nature of antiferroelectricity and its evolution with the electric field and temperature remain controversial, mostly due to the difficulty of obtaining high-quality single-crystal samples. The lack of consensus regarding the phase transition in PbZrO3 is not only important on a fundamental side but also greatly hinders further applications. Herein, high-quality PbZrO3 epitaxial thin films are successfully fabricated by pulsed laser deposition. The structural and physical properties of the films are systematically studied via a combination of electric property measurements, X-ray diffraction, scanning transmission electron microscopy imaging, and second-harmonic generation studies. Our studies unveil the noncentrosymmetric nature of PbZrO3 films at room temperature. Moreover, the Curie temperature increased to 270°, ∼40° higher than that in the bulk, and no intermediate ferroelectric phase was observed. Besides, an incipient ferroelectric with relaxor-like behavior above the Curie temperature due to the existence of a local polar cluster in the high-temperature paraelectric phase is experimentally observed for the first time. Our studies provide a better understanding of PbZrO3 thin films and pave the way for practical applications of antiferroelectric material in modern electronic devices.

Evolution of weak ferroelectricity dielectric response in PbZrO3 antiferroelectric thin films

Evolution of weak ferroelectricity dielectric response in PbZrO3 antiferroelectric thin films

Antiferroelectric-ferroelectric phase transition and negative electrocaloric effect in alkaline-earth element doped PbZrO3 thin films

Electrocaloric effect (ECE) in dielectric materials has attracted much attention due to its promising applications in solid-state cooling devices. In this work, alkaline-earth doped PbZrO3 antiferroelectric thin films (Pb0.9A0.1ZrO3 (A=Ca, Sr, and Ba)) were deposited by a sol-gel method and its antiferroelectric-ferroelectric phase competition as well as the negative ECE were studied. It is found that Ca2+ and Sr2+ expand the antiferroelectric phase region while Ba2+ reduces it, due to the different ion radii of these alkaline-earth elements. As a result, the Pb0.9Sr0.1ZrO3 thin film exhibits an enhanced negative ECE with ΔT of around − 10.6 K under 450 kV/cm whereas the Pb0.9Ba0.1ZrO3 thin film shows a decreased negative ECE with ΔT of around − 2.5 K under 200 kV/cm, as compared with the pristine PbZrO3 thin films (with ΔT of around −7.3 K under 300 kV/cm). This work provides an effective method to enhance the negative ECE of antiferroelectrics in electrical cooling applications by adjusting their antiferroelectric to ferroelectric phase transition.

Effect of ferroelectric domain walls on the dielectric properties of PbZrO3 thin films

In antiferroelectric PbZrO3 thin films, a weak residual ferroelectric phase is often observed on the double hysteresis loop and it is important to know its impact on the dielectric properties. To study this residual phase, a low and homogeneous electric field can be used because antiferroelectric domain walls are not sensitive to homogeneous fields; thus, contributions of ferroelectric domain wall motions to permittivity and dielectric losses can be isolated. In this paper, the hyperbolic law characterization is used on lead zirconate thin films, which present a residual ferroelectric phase. The study shows that domain wall contributions of the ferroelectric phase are small (less than 2% of the total permittivity), but their impacts are very important in the overall dielectric losses (≈26%). These losses are, however, lower than those obtained in pure ferroelectric materials due to a residual state composed of well distributed ferroelectric clusters of small size with no interactions between domain walls.

Tailoring the negative electrocaloric effect of PbZrO3 antiferroelectric thin films by Yb doping

A novel electrocaloric material system, Yb doped PbZrO3 (PYZ) antiferroelectric (AFE) thin films with the content of Yb from 0 to 3.0 mol% were fabricated by the sol-gel method. The influence of the Yb contents on the orientation degree and the negative electrocaloric effect (NECE) of PYZ AFE thin films were investigated. We found a giant NECE (ΔT = −12.01 K) and an entropy variation of −11.8 J kg−1 K−1 for the 1.0 mol% Yb doped PbZrO3 thin films at 70 °C with the applied electric of 800 kV cm−1 calculated on account of the Maxwell equation. These results suggested the large NECE can be acquired via Yb doping and raised hopes for the development mid- to large-scale solid-state cooling devices with high efficiency in combination with positive ECE.

Understanding the effects of electric-field-induced phase transition and polarization loop behavior on the energy storage performance of antiferroelectric PbZrO3 thin films

Antiferroelectric PbZrO3 (PZO) thin-films were fabricated by pulsed laser deposition (PLD) and sol-gel techniques to investigate the effect of antiferroelectric-ferroelectric (AFE-FE) phase transition on the energy storage performance. The (100)-oriented PLD thin-films have a square-double polarization-electric field (P-E) hysteresis loop with a sharp-phase transition and the (111)-oriented sol-gel thin-films have a slanted P-E loop with a diffused-phase transition. The difference in the phase transition fields between PLD and sol-gel thin-films could be attributed to their difference in crystalline orientations. In this case, the antipolar AFE phase is along the [110]-direction of the original tetragonal-cell under zero electric-field, while the antipolar AFE phase switches into the polar FE phase under a strong enough electric-field and the tetragonal-cell becomes rhombohedral with the polar direction of [111]. Due to the larger maximum polarization and slimmer P-E loop, the higher recoverable energy-storage (Ureco) of 19.4 J/cm3 and larger energy-efficiency (η) of 70.8%, are achieved in sol-gel thin-films. More importantly, this film shows excellent charge-discharge cycling endurance of both Ureco and η values after 1010 cycles and good thermal-stability under a wide operating temperature. From the viewpoint of applications, the sol-gel method is considered to be a promising approach towards producing low-cost PZO thin-films for high-efficiency energy-storage devices over a broad temperature range.

Significantly improved energy storage properties and cycling stability in La-doped PbZrO3 antiferroelectric thin films by chemical pressure tailoring

In this work, Pb1−3x/2LaxZrO3 (x = 0–0.12) (PLZ-x) antiferroelectric thin films were fabricated on Pt(111)/TiO2/SiO2/Si substrates using chemical solution method. Smaller cations (La3+) and vacancies were introduced into A-sites of perovskite structure to construct chemical pressure. According to phenomenological theory, chemical pressure can increase the energy barrier between antiferroelectric (AFE) and ferroelectric (FE) phase, and enhance antiferroelectricity of the system. As a result, a large energy storage density (Wre) of 23.1 J cm−3 and high efficiency (η) of 73% were obtained in PLZ-0.10 films, while PLZ-0 films displayed lower Wre (15.1 J cm−3) and η (56%). More importantly, PLZ-0.10 films exhibited an excellent cycling stability with a variation of ˜2% after 1 × 108 cycles. The results demonstrate that heavily La-doped PbZrO3 films with high energy storage density, high efficiency and excellent cycling stability can be considered as potential candidates for energy storage applications.

Flexible high energy density capacitors using La-doped PbZrO3 anti-ferroelectric thin films

Flexible high energy density capacitors were fabricated by depositing 6 mol. % La-doped anti-ferroelectric PbZrO3 thin films using chemical solution deposition on ultra-thin metal foil substrates. The integration of a LaNiO3 buffer layer on the flexible austenitic metal foil substrate resulted in substantial improvements in microstructure uniformity and density of the La-doped PbZrO3 thin film capacitors. The recoverable energy density and the energy loss of the flexible thin film capacitors were 15.2 ± 0.2 J/cm3 and 4.8 ± 0.2 J/cm3 at 1 MV/cm, respectively. The La-doped PbZrO3 flexible thin film capacitors showed no noticeable degradation in ferroelectric hysteresis behavior and the energy storage density even after 1000 bending cycles.

Electrocaloric effect in PbZrO3 thin films with antiferroelectric-ferroelectric phase competition

Electrocaloric effect in antiferroelectric PbZrO3 thin films that undergo antiferroelectric-ferroelectric phase transition upon cooling down is investigated using atomistic first-principles-based simulations. It is found that such a phase transition is associated with a large positive electrocaloric response that can reach 13K under electric field of 500kV/cm. High tunability of the phase transition by the electric field leads to a wide range of temperatures associated with strong electrocaloric response. Epitaxial strain was found to provide further tunability to the electrocaloric properties. Large intrinsic electrocaloric effect at the antiferroelectric-ferroelectric phase transition and its high tunability by the electric field offer promising technological applications.

Development of High Energy Capacitors Using La-Doped PbZrO3 Anti-Ferroelectric Thin Films

Chemical solution-derived anti-ferroelectric (AFE) thin films for energy storage devices were investigated. In order to evaluate dielectric properties(dielectric constant and loss, leakage current density), anti-ferroelectric properties(energy storage density and loss, energy storage efficiency) of anti-ferroelectric thin films with lanthanum (La) as a dopant, ∼1 μm-thick anti-ferroelectric (PbLa)ZrO3 (PLZO) films as a function of La doping concentration (0 ∼ 6 mol.%) were deposited on Pt/Ti/SiO2/Si substrate. With the increase of La-doping concentration, the energy storage loss was reduced from ∼8.8 J/cm3 to ∼6.6 J/cm3, and the efficiency was increased from ∼59.2% to ∼80.7%. In terms of the lowest leakage current density, the maximum energy storage performance was observed in La 2 mol.% doped PLZO thin film capacitor with the energy storage density ∼16.9 J/cm3, energy loss ∼8.4 J/cm3 and energy storage efficiency ∼66.8% at an applied electric field ∼1 MV/cm with frequency ∼1 kHz at room temperature.

Effect of residual stress on energy storage property in PbZrO3 antiferroelectric thin films with different orientations

The effect of residual stress on energy storage property was investigated for a series of PbZrO3 thin films on SrTiO3 and Si substrates. Compressive or tensile residual stress influences the critical electric field EA for the ferroelectric-to-antiferroelectric phase transition, thus for films with (110)/(101) orientation, energy density W of films on SrTiO3 is 38% larger than films on Si; in contrast, (001)-oriented PbZrO3 films on SrTiO3 show slightly smaller W compared to films on Si. We conclude that the different responses of W to stress are related to the different constrain states in films with different orientations.

Structure and improved electrical properties of Pr-doped PbZrO3 antiferroelectric thin films with (111) preferential orientation

Pr-doped PbZrO3 antiferroelectric thin films have been fabricated on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. All the thin films with different Pr doping contents crystallized in perovskite phase with strong (111)-preferred orientation. When Pr doping amount was 1 mol%, the thin film exhibited a large saturation polarization of 59.4 μC cm−2, a high energy storage density of 14.2 J cm−3 at about 600 kV cm−1, and a dielectric constant of about 354 at 1 kHz. The high (111) orientation and occupying site of Pr ions were suggested to be responsible for the improved electrical properties of the thin films.

Effect of Nb doping on preferential orientation, phase transformation behavior and electrical properties of PbZrO3 thin films

Undoped and Nb-doped (1, 3, 5, 7 and 9mol%) PbZrO3 antiferroelectric thin films were deposited on Pt(111)/Ti/SiO2/Si substrates by using a sol–gel method. All the thin films had a perovskite phase structure and exhibited a distinct preferential orientation, phase transformation behavior and electrical properties, due to the effect of Nb doping. On the extent of Nb dopant, orientation of the films was changed from (100) to (111) gradually. Meanwhile, with increasing Nb content, a gradual change from AFE to ferroelectric at room temperature was observed. Dielectric constant as a function of Nb content was also reported. The dielectric constant increased with Nb content up to 7mol% and then decreased at 9mol% Nb. Dielectric loss remained quite low (less than 0.05) in the whole frequency or voltage ranges.

Electrical and Energy Storage Performance of Eu‐Doped PbZrO3 Thin Films with Different Gradient Sequences

The Eu‐doped compositionally graded multilayer PbZrO3 antiferroelectric thin films have been deposited on Pt(111)/Ti/SiO2/Si substrates by a sol–gel method. The effect of gradient sequence on microstructure, electrical properties, and energy storage performance has been investigated in detail. X‐ray diffraction patterns confirm that both thin films have crystallized into a unique perovskite phase. Down‐graded thin films have bigger grain sizes than up‐graded films, which is attributed to the influence of the gradient sequence of the thin films layer. The dielectric constant of down‐graded films is found to be higher than that of up‐graded films. Compared with up‐graded thin films, the energy storage density of down‐graded films is enhanced due to double hysteresis loop with small hysteresis switch, and high polarization.

Slim P-E hysteresis loop and anomalous dielectric response in sol-gel derived antiferroelectric PbZrO3 thin films

Sol-gel derived PbZrO3 (PZ) thin films have been deposited on Pt(111)∕Ti∕SiO2∕Si substrate and according to the pseudotetragonal symmetry of PZ, the relatively preferred (110)t oriented phase formation has been noticed. The room temperature P-E hysteresis loops have been observed to be slim by nature. The slim hysteresis loops are attributed to the [110]t directional antiparallel lattice motion of Pb ions and by the directionality of the applied electric field. Pure PZ formation has been characterized by the dielectric phase transition at 235°C and antiferroelectric P-E hysteresis loops at room temperature. Dielectric response has been characterized within a frequency domain of 100Hz–1MHz at various temperatures ranging from 40to350°C. Though frequency dispersion of dielectric behaves like a Maxwell–Wagner type of relaxation, ω2 dependency of ac conductivity indicates that there must be G-C equivalent circuit dominance at high frequency. The presence of trap charges in PZ has been determined by Arrhenius plots of ac conductivity. The temperature dependent n (calculated from the universal power law of ac conductivity) values indicate an anomalous behavior of the trapped charges. This anomaly has been explained by strongly and weakly correlated potential wells of trapped charges and their behavior on thermal activation. The dominance of circuit∕circuits resembling Maxwell–Wagner type has been investigated by logarithmic Nyquist plots at various temperatures and it has been justified that the dielectric dispersion is not from the actual Maxwell–Wagner-type response.

Microstructure and electrical properties of (120)O-oriented and of (001)O-oriented epitaxial antiferroelectric PbZrO3 thin films on (100) SrTiO3 substrates covered with different oxide bottom electrodes

Epitaxial antiferroelectric PbZrO3 (PZO) thin films of two different crystallographic orientations were grown by pulsed laser deposition on (100)-oriented SrTiO3 single crystal substrates. The latter were covered either with SrRuO3 epitaxial bottom electrodes, or with an epitaxial BaZrO3 buffer layer and an epitaxial BaPbO3 bottom electrode, respectively. Their crystal orientation and microstructure were characterized by x-ray diffraction, transmission electron microscopy, and electron diffraction. The orthorhombic (index O) PZO films on SrRuO3∕SrTiO3 were predominantly (120)O oriented and consisted of four azimuthal domains forming 90° and 60° boundaries, whereas those grown on BaPbO3∕BaZrO3∕SrTiO3 were (001)O oriented. All films showed well-defined double P-E hysteresis loops, four distinct switching peaks in the current-voltage characteristics, and piezoelectric double loops recorded by piezoresponse scanning force microscopy. The values of the saturation polarization PS and the critical field EC of the (120)O-oriented PZO films (PS=41μC∕cm2; EC=445kV∕cm) are different from those of the (001)O-oriented films (PS=24μC∕cm2; EC=500kV∕cm). A transition temperature to the paraelectric phase of 260°C has been found, which is 30K higher than the bulk value, probably indicating a stabilization of the antiferroelectric phase by substrate-induced strain.

Antiferroelectric thin films phase diagrams

In this article the size effects of phase transitions and polar properties of the thin antiferroelectric films are considered. We modified the phenomenological approach proposed by Kittel. The Euler--Lagrange equations were solved by direct variational method. The free energy with renormalized coefficients depending on the film thickness has been derived. The approximate analytical expression for the coefficients dependence on film thickness, temperature, polarization gradient coefficient and extrapolation lengths were obtained. It is shown how the anti-ferroelectric “double” hysteresis loop transforms into the ferroelectric “single” one under the film thickness decrease. Proposed theoretical consideration explains the experimental results obtained in antiferroelectric PbZrO3 thin films.

Oxygen vacancy defects in antiferroelectric PbZrO3 thin film heterostructures after neutron irradiation

Neutron irradiation effects on highly oriented antiferroelectric PbZrO3 (PZ) thin films are investigated in view of their possible application as a temperature sensitive element in an alternative bolometer system for fusion devices such as the International Thermonuclear Experimental Reactor (ITER). All films were prepared by a sol-gel technique or by pulsed laser deposition (PLD). The dielectric properties were investigated in a frequency range from 1 to 250kHz and at temperatures up to 400°C, prior to and after irradiation to neutron fluences of 0.5×1022, 1×1022, 2×1022, and 3×1022m−2 (E>0.1MeV). After irradiation, the films were annealed in several steps up to 400°C in order to remove the radiation-induced defects. The results are discussed in terms of a phenomenological model of radiation effects in PZ films, which takes into account structural defects, such as oxygen vacancies, and radiation-induced charges. We find that the films are most sensitive to neutron irradiation in the vicinity of the phase transistion temperature Tc. In addition, the structural order of the films as well as the interfaces play an important role. We find that the PZ heterostructures prepared by PLD are radiation harder than the sol-gel films. The dielectric properties of the PLD films are more or less unaffected by neutron irradiation up to a fluence of 3×1022m−2 (E>0.1MeV).