Room Temperature Remnant Polarization Research Articles

Achieving ultralow coercive electric field in (Ca1-1.5xGdx)3Ti2O7 ceramics via dual inhibitory effects on oxygen vacancies

(Ca1-1.5xGdx)3Ti2O7 ceramics with ultralow coercive field were obtained by the flowing oxygen sintering combined with donor doping, and their microstructure, dielectric properties ferroelectric properties, and negative piezoelectric properties were studied. The Gd3+ was introduced into A sites of Ca3Ti2O7 ceramics when x is less than 0.75%, but the Gd3+ occupied B sites of Ca3Ti2O7 ceramics when x is above 0.75%. The introduction of Gd3+ suppresses grain growth and leads to a transition from rod-like grain to irregularly shaped grain. The variation of oxygen vacancy induced by the doping of Gd3+ leads to the change of dielectric and ferroelectric properties of (Ca1-1.5xGdx)3Ti2O7 ceramics. The ultralow coercive field of (Ca1-1.5xGdx)3Ti2O7 (x = 0.25%) sample obtained at PUND and DHM modes reached 58.80 kV/cm and 45.76 kV/cm, respectively, and the higher room-temperature remnant polarization (1.797 μC/cm2/PUND and 2.055 μC/cm2/DHM) was achieved simultaneously. These results indicate that the inhibition of oxygen vacancies contributes to realizing the ultralow coercive field in (Ca1-1.5xGdx)3Ti2O7 ceramics. These findings demonstrate that introducing rare-earth ions as donor dopants into the A site of Ca3Ti2O7 ceramics combined with the flowing oxygen sintering is an essential strategy to achieve ultralow coercive field for Ca3Ti2O7-based materials.

Flash Sintered Potassium Sodium Niobate: High-Performance Piezoelectric Ceramics at Low Thermal Budget Processing.

Alternative sintering technologies promise to overcome issues associated with conventional ceramic sintering such as high thermal budgets and CO2 footprint. The sintering process becomes even more relevant for alkali-based piezoelectric ceramics such as K0.5Na0.5NbO3 (KNN) typically fired above 1100 °C for several hours that induces secondary phase formation and, thereby, degrades their electrical characteristics. Here, an ability of KNN ceramics to be of high performance is successfully demonstrated, using an electric field- and current-assisted Flash sintering technique at 900 °C only. Reported for the first time, Flash sintered KNN ceramics have room-temperature remnant polarization Pr = 21 μC/cm2 and longitudinal piezoelectric coefficient d33 = 117 pC/N, slightly superior to that of conventional ones due to the reduced content of secondary phases. High-performance KNN ceramics Flash sintered at a low-thermal budget have implications for the development of innovative low carbon technologies, electroceramics stakeholders, and piezoelectric energy harvesters.

The enhanced ferroelectricity in Sr1-δTiO3/BaTiO3 superlattices with Sr deficiency

Here we report the tunable ferroelectricity in superlattices of (Sr1-δTiO3)n/(BaTiO3)8 with δ≈ 5% and the maximally enhanced ferroelectricity is found in the n= 6 superlattice. The room-temperature remnant polarization of n =6 is enhanced by 70% and 1120% compared to those of BaTiO3 and Sr1-δTiO3 thin films, respectively. The ferroelectric transition temperature of n =6 is 40 K higher than that of the BaTiO3 film, and is independent of the measurement frequency. The dependence of remnant field 2Pr on n coincides well with the n dependence of γ/α, which is ratio between out-of-plane and in-plane octahedral rotation angles. It thus suggests a strong correlation between the octahedral rotation pattern and the ferroelectric distortion. Our study demonstrates the importance of constructing superlattices to enhance the ferroelectric properties of the defect-engineered materials to be better than the pristine materials.

Lead zirconate titanate and barium titanate bi-layer ferroelectric films on Si

In this work, a novel method is proposed to integrate ferroelectric lead zirconate titanate (PZT) films on Si with highly tunable functionalities, through bi-layering with a barium titanate (BTO) film. First of all, the BTO film acts as a growth-promotion template layer which has successfully lowered the in situ deposition temperature of a ferroelectric PZT film. The PZT/BTO bilayer film deposited at 350 °C on LaNiO3-buffered Si substrate displayed a room temperature remnant polarization ∼24 μC/cm2, and its quality can be further improved via a rapid thermal annealing (RTP) process. Furthermore, by changing their thickness ratio, various ferroelectric hysteresis loops (P-E loops) can be created in the PZT/BTO films, thereby enabling a broad range of applications for this simple bi-layer structure. Examples including high performance piezoelectric energy harvesters and high energy density dielectric capacitors are demonstrated for the PZT/BTO bi-layer films.

Lead-free perovskite ferroelectric thin films with narrow direct band gap suitable for solar cell applications

[KNbO3]0.9[BaNi1/2Nb1/2O3]0.1 (KBNNO) perovskite ferroelectric thin films with narrow band gap (up to 1.39eV) and good ferroelectric properties are prepared successfully by pulsed laser deposition. The emergence of Ni 3d gap states is confirmed to be responsible for the narrowing down of band gap of KBNNO, which correlates almost linearly with the increase of Ni content. Via a linear fit, a quantitative relationship between the Ni content and the band gap is established, laying a foundation for future design of new KBNNO-based materials with narrow band gap. The room-temperature remnant polarization (up to 1.4μC/cm2) of the KBNNO thin film is by an order of magnitude higher than that (0.1μC/cm2) of previously reported thick film with 20μm thickness. Both narrow band gap and large room-temperature remnant polarization make KBNNO thin films very attractive for developing ferroelectric photovoltaic devices with high conversion efficiencies.

Metalorganic solution deposition of lead zirconate titanate films onto an additively manufactured Ni-based superalloy

Recent advances in additive manufacturing of high-temperature alloys for structural aerospace applications has led to interest in integrating additional functionality into such parts. Lead zirconate titanate (PZT) is a prototypical ferroelectric ceramic used as the electro-active material in many piezoelectric sensors and actuators. In this study, 300 nm thick PbZr0.2Ti0.8O3 (PZT 20/80) films were grown using metalorganic solution deposition onto additively manufactured substrates of Inconel 718. The microstructures of the films and the nature of the film/substrate interfaces were characterized using a combination of X-ray diffraction and electron microscopy techniques. Electrical measurements were performed to determine the ferroelectric, dielectric, and conductive responses of the PZT films. Our findings show that the PZT films exhibit robust ferroelectricity characterized by well-defined polarization-applied electric field (P-E) hysteresis loops. The samples display internal bias of up to ∼40 kV/cm. The room temperature remnant polarization and the small signal dielectric permittivity are ∼70 μC/cm2 and 205, respectively. The dielectric loss (tan δ) and the leakage current at 1 kHz are 9% and 1 nA at 1 V, respectively. We attribute the internal bias observed in the hysteresis loops and the overall large dielectric losses to the presence of an intermediate oxide layer at the PZT/Inconel interface, which forms during the high temperature crystallization of the ferroelectric film. These results show that it is possible to grow functional oxides with promising electrical properties onto additively manufactured metallic substrates.

Ferroelectric and magnetic properties in 85 nm-thick Bi6Fe2Ti3O18 thin films by a modified sol-gel processing

Bi6Fe2Ti3O18 thin film on Pt/Ti/SiO2/Si substrate with a thickness of 85 nm is successfully prepared by a monoethanolamine-modified sol-gel processing. The prepared thin film is polycrystalline and shows dense morphology. The room temperature remnant polarization is higher than 10 μC cm−2 at 5 V driving voltage both from polarization-voltage hysteresis loop and positive-up negative-down measurements. The polarization after 107 switching cycles and a retention time of 104 s shows no obvious degradation, suggesting good fatigue-resistant characteristics. Weak ferromagnetism is observed at 5 K with a saturated magnetic moment of 11.7 emu/cm3. The results will provide an effective route to optimize Bi6Fe2Ti3O18 thin films with thickness below 100 nm by low-voltage driving.

The structural and in-plane dielectric/ferroelectric properties of the epitaxial (Ba, Sr)(Zr, Ti)O3 thin films

Epitaxial (Ba1-xSrx)(Zr0.1Ti0.9)O3 (BSZT, x = 0 – 0.45) thin films were deposited on (LaAlO3)0.3(Sr2AlTaO6)0.35 (LSAT) substrates by pulsed laser deposition. The experimental results demonstrate that the structural, dielectric, and ferroelectric properties of the BSZT thin films were greatly dependent on the strontium content. The BSZT thin films transformed from tetragonal to cubic phase when x ≥ 0.35 at room temperature. The Curie temperature and room-temperature remnant polarization decrease with increasing strontium concentration. The optimal dielectric properties were found in (Ba0.55Sr0.45)(Zr0.1Ti0.9)O3 thin films which is in paraelectric state, having tunability of 47% and loss tangent of 0.0338 under an electric field of 20 MV/m at 1 MHz. This suggests that BSZT thin film is a promising candidate for tunable microwave device applications.

Structural and electrical characterizations of Bi(Zn0.5Ti0.5)O3 doped lead zirconate titanate ferroelectric films with enhanced ferroelectric properties

Bi(Zn0.5,Ti0.5)O3 (BZT) doped Pb(Zr0.4,Ti0.6)O3 (PZT) films were fabricated using a chemical solution deposition method and were characterized intensively in the present work. It was discovered that the room temperature remnant polarization and zero-field longitudinal piezoelectric constant of the BZT-doped PZT film were enhanced by 23% and 30%, respectively, as compared with those of the undoped PZT film prepared under the same experiment conditions. In order to explain the improved ferroelectric properties, the phase structures of the BZT–PZT and undoped PZT films were experimentally investigated in a broad temperature range (from 30 to 600°C) by using the high temperature two-dimensional X-ray diffraction method. It was found that the improvement in ferroelectricity does not correspond to an elevated Curie temperature (TC) or a substantially larger tetragonality (c/a). The difference on the change of TC by doping of Bi-based perovskites in PZT solid solutions between this work and some previous investigations was explained on the basis of Zr/Ti ratio, and the necessity of an in-depth theoretical investigation was addressed.

Structural, ferroelectric and impedance spectroscopy properties of Y3+ modified Pb(Fe0.5Nb0.5)O3 ceramics

Some ceramic samples of Pb1−xYx(Fe0.5Nb0.5)1−x/4O3 (PYFN) (0.00≤x≤0.08) were synthesized by a mixed oxide route. X-ray diffraction patterns of all the above samples confirm the formation of single phase material crystallizing in monoclinic structure. Dielectric properties (εr and tanδ) were analyzed in a wide temperature (30–350°C) and frequency range (100Hz–1MHz). Ferroelectric properties of these compounds were confirmed from polarization (P–E hysteresis loop) measurements at room temperature. All the room temperature hysteresis loops of PYFN ceramics were well simulated using the ferroelectric capacitor model. Yttrium substitution resulted in notable enlargement of room temperature remnant polarization (2Pr). The 2Pr of PYFN (x=0.02) reaches to a large value (23μC/cm2), which is nearly 5 times greater than that of PFN ceramic (4.6μC/cm2). All the compounds exhibits negative temperature coefficient of resistivity (NTCR) type behavior as that of semiconductors. Dc conductivity (estimated via bulk resistivity) variation with temperature of all the samples follows Arrhenius type of electrical conductivity.

Dielectric and ferroelectric properties of strain-relieved epitaxial lead-free KNN-LT-LS ferroelectric thin films on SrTiO3 substrates

We report the growth of single-phase (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrRuO3 coated ⟨001⟩ oriented SrTiO3 substrates by using pulsed laser deposition. Films grown at 600°C under low laser fluence exhibit a ⟨001⟩ textured columnar grained nanostructure, which coalesce with increasing deposition temperature, leading to a uniform fully epitaxial highly stoichiometric film at 750°C. However, films deposited at lower temperatures exhibit compositional fluctuations as verified by Rutherford backscattering spectroscopy. The epitaxial films of 400–600nm thickness have a room temperature relative permittivity of ∼750 and a loss tangent of ∼6% at 1kHz. The room temperature remnant polarization of the films is 4μC∕cm2, while the saturation polarization is 7.1μC∕cm2 at 24kV∕cm and the coercive field is ∼7.3kV∕cm. The results indicate that approximately 50% of the bulk permittivity and 20% of bulk spontaneous polarization can be retained in submicron epitaxial KNN-LT-LS thin film, respectively. The conductivity of the films remains to be a challenge as evidenced by the high loss tangent, leakage currents, and broad hysteresis loops.

Solid film lubricants

Recent advances in additive manufacturing of high-temperature alloys for structural aerospace applications has led to interest in integrating additional functionality into such parts. Lead zirconate titanate (PZT) is a prototypical ferroelectric ceramic used as the electro-active material in many piezoelectric sensors and actuators. In this study, 300 nm thick PbZr0.2Ti0.8O3 (PZT 20/80) films were grown using metalorganic solution deposition onto additively manufactured substrates of Inconel 718. The microstructures of the films and the nature of the film/substrate interfaces were characterized using a combination of X-ray diffraction and electron microscopy techniques. Electrical measurements were performed to determine the ferroelectric, dielectric, and conductive responses of the PZT films. Our findings show that the PZT films exhibit robust ferroelectricity characterized by well-defined polarization-applied electric field (P-E) hysteresis loops. The samples display internal bias of up to ∼40 kV/cm. The room temperature remnant polarization and the small signal dielectric permittivity are ∼70 μC/cm2 and 205, respectively. The dielectric loss (tan δ) and the leakage current at 1 kHz are 9% and 1 nA at 1 V, respectively. We attribute the internal bias observed in the hysteresis loops and the overall large dielectric losses to the presence of an intermediate oxide layer at the PZT/Inconel interface, which forms during the high temperature crystallization of the ferroelectric film. These results show that it is possible to grow functional oxides with promising electrical properties onto additively manufactured metallic substrates.