Niobium-doped Lead Zirconate Titanate Research Articles

Additive Manufacturing of Piezoelectric Niobium-Doped Lead Zirconate Titanate (PZT-N) by Binder Jetting

Binder jetting is an emerging indirect additive manufacturing technique for ceramic materials, which could be employed to produce application-oriented designed components impossible to achieve with traditional processes and featuring enhanced performances. In our study, niobium-doped lead zirconate titanate (PZT-N) powder, usually processed through the standard press-and-sinter route, was employed as the raw material. First, the powder was characterized in terms of granulometry and flowability to assess its suitability for the printing process. Then, shaping by binder jetting was studied, and the effect of three levels of binder saturation (75–90–105%) on the green bodies was assessed. Finally, the microstructure of the sintered samples was studied using SEM, to investigate the effect of thermal treatments on the grain size distribution and residual porosity (~40%). The piezoelectric properties were measured and compared to those of conventionally processed material. The piezoelectric charge and voltage constants (d33 and g33) were evaluated to determine the possible use of printed parts as porous piezoelectric components to be exploited in hydrophones in the direct mode.

Resistive properties of CuInS<sub>2</sub> quantum dots regulated by niobium-doped lead zirconate titanate ferroelectric films

As a new type of non-volatile memory, quantum dot resistive random access memory (RRAM) has attracted much attention for its easy preparation, fast responding time, high storage density, and smaller device size. CuInS<sub>2</sub> quantum dot (CuInS<sub>2</sub> QD) is a kind of excellent resistive functional material with abundant electron capture sites, high optical absorption coefficient, and high carrier mobility. In this work, CuInS<sub>2</sub> QDs/Nb:Pb (Zr<sub>0.52</sub>Ti<sub>0.48</sub>)O<sub>3</sub> (PNZT) films are prepared by spin-coating CuInS<sub>2</sub> QDs on PNZT films. The results show that the resistive properties of CuInS<sub>2</sub> QDs RRAMs can be effectively improved by introducing PNZT films and can be controlled by changing the polarization direction. The CuInS<sub>2</sub> QDs/PNZT film in the negative polarization state promotes the interfacial electrons to enter into the PNZT film, which will reduce the height of the interfacial barrier and the thickness of the interfacial depletion region. And it will reduce the resistance of the composite film at the low resistance state (LRS). Compared with the switching voltage and resistive switching ratio of the pure CuInS<sub>2</sub> QDs film (10<sup>3</sup>), the switching voltage of the device decreases to –4.1/3.4 V and the resistive switching ratio increases to 10<sup>6</sup>. Furthermore, it maintains good stability in the 10<sup>3</sup> cycle durability test. In contrast, the CuInS<sub>2</sub> QDs/PNZT film interface has a larger barrier height and depletion-layer thickness when the PNZT is in the positive polarization state, which increases the resistance of the composite film in the LRS state. As a result, the switching voltage of the device increases to –6.4/5.7 V with a resistive switching ratio of 10<sup>4</sup>. The resistive properties of the CuInS<sub>2</sub> QDs/PNZT film can be tuned by changing the polarization direction, as the polarization direction of the PNZT changes the interfacial energy band structure and affects the conduction mechanism. This work reveals the feasibility of using ferroelectric thin films to improve the resistive properties of quantum dots RRAMs and thus providing an approach to further developing RRAMs.

Influence of graded doping on the long-term reliability of Nb-doped lead zirconate titanate films

Niobium doped lead zirconate titanate (PNZT) films show potential in piezoelectric microelectromechanical systems (piezoMEMS); their long-term reliability is important for successful application. This work describes how variations in the doping profile through the film depth can significantly increase the long-term reliability of PNZT films, while retaining excellent piezoelectric properties. Chemical solution derived {100} textured PNZT films were prepared with a Mn-doped lead zirconate titanate (PMZT) layer at the film top or bottom surface (PNZT + x mol% PMZT, or x mol% PMZT + PNZT). No significant differences were found in the baseline dielectric, ferroelectric and piezoelectric properties of the films. As the Mn-doping concentration increased, the medium time to failure (t50) of PNZT + x mol% PMZT and x mol% PMZT + PNZT films gradually increased from 14.4 h to 93.9 hours, and from 27.7 to 94.6 hours, respectively, under aggressive test conditions (200°C, 300 kV/cm) where the Mn doped layer served as the cathode. Current – voltage measurement on pristine PNZT + 2 mol% PMZT films showed Schottky emission-controlled conduction. After a 23 hours degradation period at 200°C, 300 kV/cm (field up), Poole-Frenkel conduction became dominant. The trap energy level increased from 0.45 ± 0.01 eV for PNZT to 1.27 ± 0.03 eV for the PNZT + 2 mol% PMZT film. Furthermore, Ti4+ reduction was found in degraded PNZT near the top electrode, but not in degraded PNZT + 2 mol% PMZT, as recorded by electron energy loss spectroscopy data. Electron trapping by Mn ions showed strong contributions to suppression of the conduction and improvement of long-term reliability for the PNZT film with a PMZT (top or bottom) layer.

Comparison of the Thermal Degradation of Heavily Nb-Doped and Normal PZT Thin Films.

The degradation of niobium-doped lead zirconate titanate (PZT) and two types of PZT thin films were investigated. Undoped PZT, two-step PZT, and heavily Nb-doped PZT (PNZT) around the morphotropic phase boundary were in situ deposited under optimum condition by RF-magnetron sputtering. All 2- [Formula: see text]-thick films had dense perovskite columnar grain structure and self-polarized (100) dominant orientation. PZT thin films were deposited on Pt/TiOx bottom electrode on Si wafer, and PNZT thin film was on Ir/TiW electrode with the help of orientation control. Sputtered PZT films formed on microelectromechanical system (MEMS) gyroscope and the degradation rates were compared at different temperatures. PNZT showed the best resistance to the thermal degradation, followed by two-step PZT. To clarify the effect of oxygen vacancies on the degradation of the film at high temperature, photoluminescence measurement was conducted, which confirmed that oxygen vacancy rate was the lowest in heavy PNZT. Nb-doping PZT thin films suppressed the oxygen deficit and made high imprint with self-polarization. This defect distribution and high internal field allowed PNZT thin film to make the piezoelectric sensors more stable and reliable at high temperature, such as reflow process of MEMS packaging.

Bilayer thick structures based on CoFe2O4/TiO2 composite and niobium-doped PZT obtained by electrophoretic deposition

In view of developing new structures and processes for the production of magnetoelectric materials, bilayer thick structures made of cobalt ferrite (CoFe2O4)/titanium dioxide (TiO2) composite and niobium-doped lead zirconate titanate (PZTN) were grown on silver-coated alumina substrates by electrophoretic deposition (EPD) from ethanol-based colloidal suspensions. A first co-deposition from a CoFe2O4/TiO2 suspension was followed, after heat treatments of the electrodeposited composite layer, by a second deposition from a PZTN suspension. Each deposition was performed at constant voltage while recording the current. High density structures keeping the same stoichiometry of the deposited particles were observed after sintering. Composition, thickness and relative density of the layers were investigated by Energy Dispersive X-ray Spectroscopy (EDXS) and Scanning Electron Microscopy (SEM) analyses, while the crystalline phases were identified by X-ray diffraction (XRD). Ferroelectric, hysteresis loops and piezoelectric response of the bilayer thick structures were measured resulting in good piezoelectric activity of the poled structures.

PZT-Based Thick Films Prepared by Electrophoretic Deposition from Suspensions with Different Alcohol-Based Solvents

Niobium-doped lead zirconate titanate (PZT-Nb) thick films have been prepared by electrophoretic deposition from suspensions with different alcohol-based solvents, namely ethanol or mixtures of ethanol and 10 vol.% of a co-solvent: butanol or 2-butoxyethanol. The co-solvent addition results in a modification of the suspension's properties. As a consequence, under the same deposition conditions the rate of deposit formation changes for the suspensions with different solvents. The deposits show a homogeneous packing of the particles without any appreciable variation in their green density regardless of the variations in the deposition rate. Nevertheless, the deposits with a similar mass prepared from the different suspensions show distinct morphologies, some of them being considerably thicker at the edges than at the centre. The peculiarities in the thickness uniformity observed for the as-deposited layers are ascribed to changes in the resistivity of the deposits. After sintering, the thick films obtained from the different suspensions show particular microstructures which may be related to the morphology of the as-deposited layers. Dense films with a grain size of about 2–3 μm and an enhanced ferroelectric response were obtained from the suspension containing butanol.

Lead zirconate titanate-based thick films for high-frequency focused ultrasound transducers prepared by electrophoretic deposition

An electrophoretic deposition (EPD) process with high deposition rate was used to fabricate a curved piezoelectric thick film devoted to high-frequency transducers for medical imaging. Niobium-doped lead zirconate titanate (PZTNb) powder was stabilized in ethanol to prepare a suspension with high zeta potential and low conductivity. A gold layer, pad-printed and fired on a curved porous PZT substrate, was used as the working electrode for the deposition of the PZTNb thick film. This substrate was chosen because it has the required properties (acoustic impedance and attenuation) to be used directly as a backing for the high-frequency transducer, leading to a simplified process for transducer assembly with this integrated structure. PZT-Nb thick films were also deposited by EPD on flat gold-coated alumina substrates as a reference. The thickness of the films was between 20 and 35 μm, and their electromechanical performance was comparable to standard PZT bulk ceramics with a thickness coupling factor of 48%. For the curved thick film, the thickness coupling factor was slightly lower. The corresponding integrated structure was used to fabricate a transducer with a center frequency of 40 MHz and an f-number of 2.8. It was integrated into a realtime ultrasound scanner and used to image human forearm skin; the resulting images showed, for the first time, the efficacy of the EPD process for these imaging applications.

Raman analysis of ferroelectric switching in niobium-doped lead zirconate titanate thin films

Characteristic Raman vibration modes of niobium-doped lead zirconate titanate (PNZT) are studied as a function of ferroelectric domain switching. The microstructure of PNZT is characterized by scanning electron microscopy and X-ray diffraction. Ferroelectric switching is achieved by applying voltages between the top (Au) and bottom (Pt) electrodes, while acquiring the Raman spectra in situ. Vibrational active modes associated with paraelectric and ferroelectric phases are identified after measuring above and below the ferroelectric Curie temperature, respectively. Changes in the relative intensities of the Raman peaks are observed as a function of the switching voltage. The peak area associated with the ferroelectric modes is analyzed as a function of the applied voltage within one ferroelectric polarization loop, showing local maxima around the coercive voltage. This behavior can be understood in terms of the correlation between vibrational and structural properties, since ferroelectric switching modifies the interaction between the body-centered atom (Zr, Ti or Nb) and the Pb–O lattice.

Three-dimensional micro electromechanical system piezoelectric ultrasound transducer

Here we present the design and experimental acoustic test data for an ultrasound transducer technology based on a combination of micromachined dome-shaped piezoelectric resonators arranged in a flexible architecture. Our high performance niobium-doped lead zirconate titanate film is implemented in three-dimensional dome-shaped structures, which form the basic resonating cells. Adjustable frequency response is realized by mixing these basic cells and modifying their dimensions by lithography. Improved characteristics such as high sensitivity, adjustable wide-bandwidth frequency response, low transmit voltage compatible with ordinary integrated circuitry, low electrical impedance well matched to coaxial cabling, and intrinsic acoustic impedance match to water are demonstrated.

Interactions between Lead–Zirconate Titanate, Polyacrylic Acid, and Polyvinyl Butyral in Ethanol and Their Influence on Electrophoretic Deposition Behavior

Electrophoretic deposition (EPD) is an attractive method for the fabrication of a few tens of micrometer-thick piezoelectric layers on complex-shape substrates that are used for manufacturing high-frequency transducers. Niobium-doped lead-zirconate titanate (PZT Nb) particles were stabilized in ethanol using poly(acrylic acid) (PAA). With Fourier-transform infrared spectroscopy (FT-IR), we found that the deprotonated carboxylic group from the PAA is coordinated with the metal in the perovskite PZT Nb structure, resulting in a stable ethanol-based suspension. The hydroxyl group from the polyvinyl butyral added into the suspension to prevent the formation of cracks in the as-deposited layer did not interact with the PAA-covered PZT Nb particles. PVB acts as a free polymer in ethanol-based suspensions. The electrophoretic deposition of micro- and nanometer-sized PZT Nb particles from ethanol-based suspensions onto electroded alumina substrates was attempted in order to obtain uniform, crack-free deposits. The interactions between the PZT Nb particles, the PAA, and the PVB in ethanol will be discussed and related to the properties of the suspensions, the deposition yield and the morphology of the as-deposited PZT Nb thick film.

Shift of morphotropic phase boundary in high-performance [111]-oriented epitaxial Pb (Zr, Ti) O3 thin films

High-performance epitaxial niobium-doped lead zirconate titanate thin films [Pb(ZrxTi1−x)0.98Nb0.02O3] with a fixed thickness were deposited on [111]-cut single-crystalline SrTiO3 substrates by a sol-gel process as a function of Zr/Ti ratio ranging from 20/80 to 80/20. An obvious shift of morphotropic phase boundary (MPB) was observed in the [111]-oriented epitaxial films. Deviating from the Zr/Ti ratio of 52/48 in bulk materials, the MPB composition in the as-deposited films was found to move to a lower Zr/Ti ratio between 30/70 and 40/60, which agrees with the theoretical analysis on the basis of lattice mismatch between films and substrates and is further confirmed by the XRD patterns and Raman spectrum as well as ferroelectric test. Furthermore, a superior remnant polarization (Pr) value among all the compositions was obtained at a Zr/Ti ratio of 30/70, indicating that the extrinsic ferroelectric polarization near the new morphotropic phase boundary will lead to outstanding dielectric and piezoelectric performance in the epitaxial PZT thin film system.

The effect of a hydrostatic pressure induced phase transformation on the unipolar electrical response of Nb modified 95/5 lead zirconate titanate

Niobium doped lead zirconate titanate (95/5 NbPZT) undergoes a hydrostatic pressure induced ferroelectric rhombohedral to antiferroelectric orthorhombic phase transformation (FE-AFE). This work reports on the experimental characterization of the large field dielectric response to unipolar electric field as it passes through the forward and reverse FE-AFE transformations. The poled ceramic was hydrostatically depoled by driving the FE-AFE phase transformation and stress-strain and stress-electric displacement responses were measured. After this initial characterization, specimens of 95/5 NbPZT were subjected to unipolar electric field loading at different hydrostatic pressure levels. Electric field was varied from zero to 1 MV/m at a series of fixed pressure levels between zero and 550 MPa. This resulted in minor hysteresis loops with the area inside the loops dependent on both pressure and electric field amplitude. Two different slopes were taken from the D-E loops, identified as the small field and large field slopes. Each changed with pressure and displayed distinct jumps at the forward and reverse FE-AFE phase transformations. The area within the loops in the ferroelectric regime, attributed to domain wall motion, increased as pressure was increased and dropped abruptly as the material passed through the pressure induced phase transformation.

Fabrication and transverse piezoelectric characteristics of PZT thick-film actuators on alumina substrates

Soft piezoelectrics based on niobium-doped lead zirconate titanate (PZT-5H) are used for actuator applications. Through careful control of particle dispersion in thick-film ink formulations, crack-free and dense PZT thick-films of thickness 40 μm have been fabricated on alumina substrates by screen-printing method. The transverse piezoelectric coefficient, e 31 * (= d 31/ s 11) have been determined from the tip deflection of the unimorph cantilevers. The PZT films on alumina substrates exhibited good linear piezoelectric deflection to the applied voltage with the stable piezoelectric coefficient, e 31 * of −4.0 C/m 2.

Bipolar Electric Fatigue in Ferroelectric Nb-Doped PZST Ceramics

Bipolar electric fatigue in ferroelectric niobium-doped lead zirconate titanate stannate ceramics was investigated. Variations in the polarization and strain hysteresis loops as well as microstructural modifications of the material due to the electric cycling were analyzed. Compared with ferroelectric PZT ceramics cycled under similar conditions, the material exhibited a higher resistance to electric fatigue. Properties of the specimens showed significant decays above 106.5 cycles. Asymmetric suppression of strain hysteresis loop was monitored. At 108 cycles, the remanent polarization, the right maximum strain and the left maximum strain decreased to 70%, 58% and 44% of their initial values, respectively. The color of the material was changed from pale yellow to dark grey with cycling. The properties and color of the fatigued samples were recovered almost fully to those of the virgin state after a heat treatment at 500oC for 1 h. The pinning of domain walls, probably by oxygen vacancies, was concluded to be the predominant fatigue mechanism for the material.

Depolarization of a piezoelectric film under an alternating current field

In this article, we demonstrate that a sol-gel-derived niobium-doped lead zirconate titanate film can be depolarized by the application of alternating current (ac) fields of diminishing amplitude and we explain the phenomenon based on the concept of the Preisach model. The amplitude of the ac fields is decreased from 20 to 2 MV/m in ten steps. The observed piezoelectric coefficient of the film decreases after each ac field step. Depending on the initial polarization and the direction of the ac fields, the piezoelectric coefficient can decrease to a very small value indicating the complete depolarization of the film. Our results reveal the existence of a distribution of the switching fields in the microdomains (Preisach dipolar units), and that because of mutual interactions the magnitudes of the switch-up and switch-down fields for each microdomain are not necessarily the same. Our results also suggest that the sputter deposition of the top electrode can induce more “down-state” microdomains, thus giving rise to an initial polarization in the film. Because of interactions with other microdomains or other effects, part of these microdomains exhibit very high switching fields.

Synthesis of Nb Doped Lead Zirconate Titanate by Chemical Methods

This paper shows the results of different chemical syntheses: sol‐gel, spray‐drying, coprecipitation, involved in the production of niobium doped lead zirconate titanate ceramic materials. The formation of pure perovskitic phase at temperatures 300–400 °C lower than the traditional mixed oxide method confirmed the potentiality of the spray‐drying and sol‐gel as simple synthesis processes to produce chemically homogeneous and very reactive powders. The thermal and structural evolution of precursor powders was investigated through TG/DTA, IR and XRD analyses. The microstructures of powders and sintered bodies were presented and related to the synthesis process.

Nb-Doped PZT Material by Sol-Gel Combustion

Nanocrystalline niobium doped lead zirconate titanate powders (PZTN) were prepared by a citrate-nitrate sol-gel combustion technique. The technique involves three steps: preparation of stable and homogeneous sol, formation of gel, combustion of gel. The sol was prepared by mixing stable solutions of Zr-oxynitrate, Pb-citrate, Nb- and Ti-peroxo-citrate precursors. The heat induced auto ignition leads to the decomposition of precursors and formation of pure perovskite phase after soaking at 400∘C for 4 h. The particles were found to be irregular aggregates of nanosized primary particles (crystallite size about 30 nm). Different milling treatments were performed in order to improve the sinterability. Ball milled (100 h with PEG) powders were sintered at 1100∘C for 2 h in air showing 97% relative density at a densification T 100∘C lower than following the conventional mixed oxide route. The stoichiometry of the system was determined at each stage of the process and no fluctuation was detected.

Contribution to the comprehension of dissipation phenomena in lead zirconate titanate: aliovalent doping effect

Abstract By the solid reaction method, undoped, potassium doped and niobium doped lead zirconate titanate (PZT) are elaborated. The mechanical losses measured in the range of the Hz as a function of temperature shows two peaks R 1 and R 2 , and a ferroelectric transition peak P 1 between ferroelectric and para-electric states on the undoped PZT—Pb(Zr 0.54 Ti 0.46 )O 3 —noted PZT54/46. Potassium doped PZT—Pb 1− x K x (Zr 0.54 Ti 0.46 )O 3 —shortly called PKZT 100 x /54/46 shows an increase in the height of both the peaks at a doping content, x , less than 0.5 at.% but an opposite effect is observed above this value. Niobium doped PZT—Pb[(Zr 0.54 Ti 0.46 ) 1− y Nb y ]O 3 —shortly called PNZT 100 y /54/46, shows the vanish of the R 2 peak and the decrease of the height of the R 1 peak when the doping content increases.

Lead germanium oxide sinter-assisted PZT composite thick films

Abstract Thick films of niobium doped lead zirconate titanate (PNZT) were prepared from a sol-gel/PZT powder composite slurry. The effects of adding different amounts of sol-gel derived lead germanium oxide (PGO) as sintering aid were examined. Four layers of composite, with intermediate sol infiltrations, were deposited by spinning onto Pt/Ti/SiO 2 /Si substrates followed by drying and annealing. Addition of PGO enhanced the densification process at a temperature as low as 770 °C. It resulted in an increase in the film properties that depended upon the level of PGO addition. Film properties were assessed by measuring the capacitance and dielectric loss. d 33,f and e 31,f piezoelectric coefficient measurements were carried out after poling at 10 V/μm for 5 min at 130 °C. A maximum relative permittivity of 500 was observed between 5 and 8 wt.% PGO addition. The maximum in d 33,f was found to be about 40 pC/N. Additions between 7 and 10 wt.% PGO led to the maximum e 31,f piezoelectric coefficient of about −1.5 C/m 2 .

Microstructural characterization of donor-doped lead zirconate titanate films prepared by sol–gel processing

Lanthanum and niobium-doped lead zirconate titanate, Pb(Zr,Ti)O 3, (PZT) thin films were prepared on Pt/Ti/SiO 2/Si substrates by sol–gel processing. Films have a Zr/Ti ratio of 52:48 and tetragonal perovskite phase structure. The influence of donor dopants on the morphology, texture and defects of PZT films was studied using X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, breakdown field strength and fatigue. Donor doping of PZT films results in increased breakdown field strength and improved fatigue properties. These originate from (i) the reduction of texture in the [111] and increase in the texture in [100]; (ii) lower porosity, smaller grain size and smoother surfaces; (iii) granular grain structure; and (iv) reduction in the oxygen vacancy concentration in the films.