Ti-rich PZT Research Articles

Synthesis of Pb(Zr, Ti)O3 fine ceramic powder at room temperature by dry mechanochemical solid-state reaction evaluated using synchrotron radiation X-ray diffraction

The validity of the mechanochemical solid-state reaction by dry ball milling for synthesizing Pb(Zr, Ti)O3 (PZT) fine ceramic powder at room temperature (RT) was evaluated using synchrotron radiation X-ray diffraction (SXRD). A mixture of PbZrO3 (PZ) and PbTiO3 (PT) powders with a molar ratio of 1:1 was prepared as the starting powder. To confirm the synthesis of PZT, the structural characteristics of the ball-milled samples with different milling times were investigated by analyzing the SXRD data using the Rietveld method. The solid-state reaction was nearly complete in a short milling time of 4 h at RT. After ball milling for approximately 8 h, only a single phase of PZT was detected. The Rietveld refinement for the crystal structure analysis demonstrated that slightly Ti-rich PZT, Pb(Zr0.485(1)Ti0.515(1))O3, with a tetragonal crystal system, is synthesized in the 8 h sample. The tetragonality is sufficiently suppressed to resemble a cubic system even at RT, whereas the phase transition temperature (T C) is significantly high. We quantitatively demonstrate that PZT with a higher T C can be synthesized at RT by dry ball milling, despite the smaller spontaneous lattice distortion.

휴대용 의료 초음파 프로브 적용을 위한 압전체 제조 및 특성

Ultrasound imaging by using piezoelectric materials, such as lead zirconium titanate (PZT) has been one of the most preferred modes of imaging in the medical field due to its simple, low cost and non-ionizing radiation in comparison to other imaging techniques. Recently, the market demand for portable ultrasound is becoming larger with applications in developing countries, disaster area, military, and emergency purposes. However, most of ultrasound probes used is bulky and high power consumable, so unsuitable for such applications. In this study, the 3 layered ceramic specimen consisted of 128 pitches of <TEX>$420{\mu}m$</TEX> in width and <TEX>$450{\mu}m$</TEX> in thickness were prepared by using the Ti-rich PZT compositions co-fired at <TEX>$1,050^{\circ}C$</TEX>. Their electrical and ultrasound pulse-echo properties were investigated and compared to the single layer specimen. The 3 layered ultrasound probe showed 1.584 V of Vp-p, which is 3.2 times higher than single layered one, implying that it would allow effectively such a portable ultrasound probe system. The result were discussed in terms of higher capacitance, lower impedance and higher dielectric coefficient of the 3 layered ultrasound probe.

Composition dependent preferential orientation, dielectric and ferroelectric properties of Pb(Zr xTi 1 − x)O 3 thin films derived by sol–gel process

Pb(Zr x Ti 1 − x )O 3 ( x = 0.35, 0.40, 0.60, 0.65) thin films were prepared by sol–gel spin on technique. From the X-ray diffraction analysis, PZT films with Zr-rich compositions ( x = 0.60 and 0.65) had (111) preferential orientation and the preferential orientation changed to (100) for Ti-rich compositions ( x = 0.35 and 0.40). The dielectric measurements on the above compositions at room temperature showed that the dielectric constant values were higher in Zr-rich compositions compared to Ti-rich compositions. The ferroelectric behavior measured in terms of the remnant polarization (P r) and coercive field (E c) up to an applied field of 260 kV/cm depicted that the Zr-rich PZT films with (111) preferential orientation had higher P r and lower E c values compared to the Ti-rich PZT films with (100) preferential orientation can be understood from the domain switching mechanism.

New aspects in the (x-P-T) phase diagram of Pb(Zr1-xTix)O3materials (PZT)

PZT solid solutions were studied as a function of pressure and temperature by neutron and x-ray diffraction, Raman spectroscopy and dielectric measurements. Pressure was found to favour low-symmetry structures (Cm, Cc, F1, F1) characterized by a rotation and a reduction of the spontaneous polarisation and by the tilting of (Zr,Ti)O 6 octahedra leading to unit cell doubling (except Cm space group). Additionally, our results show that for Ti-rich PZT. high pressures stabilize the ferroelectric monoclinic phases responsible for the high piezoelectric properties of the MPB composition.

Effect of Pb(Zr xTi 1− x)O 3 composition on crystallographic texture in PZT composites

Textured Pb(Zr x Ti 1− x )O 3 ceramics with 〈1 1 1〉 orientation were prepared by the templated grain growth (TGG) method using platelike Ba 6Ti 17O 40 hetero-template grains, and the effects of matrix composition ( x value) on the texture development were examined. The template grains gave 〈1 1 1〉-texture in Ti-rich PZT ( x = 0–0.5) but did not in Zr-rich PZT ( x = 0.7–1). The matrix composition determined the extent of reaction between PZT and Ba 6Ti 17O 40, which hindered the texture development because of the disappearance of template grains at high temperatures. The matrix composition had another effect on the texture development; the texture developed by the solution of PZT in a liquid phase and the precipitation on the template grains, and the matrix composition determined the rates of these reactions.

Ferroelectric properties of nano-size PZT grains determined by surface potential utilizing Kelvin force microscopy

An attempt has been made in this work to evaluate the ferroelectric properties of PZT grains by monitoring their surface potential using scanning probe microscopy (SPM). The variations of hysteretic and retention properties were compared as a function of grain size. The smaller grain yields lower value of the surface potential than the larger grain does at the same write voltage. However, the normalized surface potential plot with respect to write voltages shows that the smaller grain tends to be saturated earlier as the writing voltage increases. The surface potential hysteretic loop obtained from the small grain shows a similar shape that can be obtained from Ti-rich PZT film, whereas that obtained from the larger grain shows a similar shape of Zr-rich PZT film. The time-dependent behavior of the surface potentials was measured as a function of an elapsed time. The utilization of SPM would provide a useful characterizing method for the nano-scaled PZT and BLT ferroelectric films.

Crystal structure and microstructure of lead zirconate titanate (PZT) thin films with various Zr/Ti ratios grown by hybrid processing

Lead zirconate titanate (Pb(Zr x Ti 1− x )O 3: PZT) thin films were fabricated on Pt/Ti/SiO 2/Si(1 0 0) substrates by a hybrid process comprising the sol–gel method and pulsed-laser deposition, using various targets of Pb(Zr x Ti 1− x )O 3 with Zr/Ti ratios of 70/30, 58/42, 52/48, 45/55 and 30/70. The effect of Zr/Ti ratio on the crystal structure and microstructure of the PZT films was investigated. The results of X-ray diffraction analysis indicated that the Zr/Ti ratio of the films fabricated using the target with a Zr/Ti ratio of 45/55 is close to that of the morphotropic phase boundary. The rosette structure was observed in Zr-rich PZT films, but not in Ti-rich PZT films. The PZT films fabricated using the target with a Zr/Ti ratio of 45/55 had a polycrystalline columnar microstructure extending throughout their thickness, and no pyrochlore phase on the surface was observed.

Electronic Structure and Chemical Bonding of Zr Substitution of Ti Site on Pb(Zr1 −xTix)O3 Using DV-Xα Method

Electronic structures were investigated on Pb(Zr1 −xTix)O3 (PZT) using the discrete variational Xα cluster method for obtaining the information of dependence on the amount and position of the substituted Zr atoms. Also, we investigated the effect of them on fatigue. The net charge and the overlap population were discussed together with the energy gap, which is related to fatigue. As a result, the net charge was independent on the amount and position of the substituted Zr atoms, and the overlap population wasn't. Furthermore, from the calculated energy gap, we conclude that Zr-rich PZT is less susceptible to fatigue than Ti-rich PZT.

Effect of Zr/Ti Ratios on Characterization of Pb ( ZrxTi1 − x ) O 3 Thin Films on Al2 O 3 Buffered Si for One-Transistor Memory Applications

(PZT) thin films have been prepared on and substrates, respectively. On substrates, Ti-rich PZT thin films had lower perovskite transformation temperatures than those of Zr-rich PZT films. Therefore, was used as the seeding layer on to form a substrate. The threshold voltage shift of a capacitor reaches 9 V with ±10 V writing voltages, which is much larger than the 2 V of the capacitor. Different memory mechanisms in the capacitance-voltage characteristics of capacitors were further examined and discussed in this paper. © 2003 The Electrochemical Society. All rights reserved.

Growth of epitaxial tetragonal Pb(Zr,Ti)O3thin films with 100% polar-axis-orientation and their electrical properties

ABSTRACTPb(ZrxTi1-x)O3(PZT) thin films with the various Zr/(Zr+Ti) ratios and the film thickness of 50 and 250 nm were epitaxiallly grown on (100)cSrRuO3//(100)SrTiO3substrates by metalorganic chemical vapor deposition at 540 °C. 50 nm-thick tetragonal PZT films consistd of 100%c-axis-orientation for the Zr/(Zr+Ti) ratio ranging from 0.13 to 0.56, while 250 nm-thick tetragonal ones consistd of about 70%c-axis-orientation for the range from 0.19 to 0.45. On the other hand, 50 and 250 nm-thick films composed rhombohedral single phase for the Zr/(Zr+Ti) ratio above 0.56 and 0.60, respectively. Mixture region of tetragonal and rhombohedral phases was observed from 0.45 to 0.60 for 250 nm-thick films, but was not for 50 nm-thick ones. Remanent polarization monotonously decreased with increasing the Zr/(Zr+Ti) ratio for 50 nm-thick films in tetragonal PZT films. These results show that Ti rich tetragonal PZT thin films have large spontaneous polarization with good square-shape hysteresis loops and are applicable for the high-density capacitor-type ferroelectric random access memories.

Chemical solution deposition of PZT thin films for microelectronics

Research into chemical solution deposition (CSD) methods for ferroelectric thin films is oriented towards higher reliability and lower processing temperatures. In this paper several aspects of CSD PZT thin films related to processing are discussed. The reliability of PZT thin films is related to their chemical homogeneity, which is connected to the chemical homogeneity of the precursor solution. In our investigation we identified the problems of the chemical heterogeneity of PZT thin-film precursors caused by the high reactivity of Zr-alkoxide. By selective modification of the Zr starting compound with acetic acid, the overall chemical homogeneity of the films was increased, which resulted in a higher P r, a lower E c, a higher permittivity and lower losses in the films. By careful control of solution chemistry and annealing conditions, Ti-rich PZT and PLZT films were successfully processed at temperatures as low as 400°C. The crystallization of these films is characterized by rapid nucleation and rapid growth. In contrast, the Zr-rich PZT and PLZT compositions require a lead titanate (PT) seeding layer for further crystallization at a temperature of 400°C. The growth of the perovskite phase is diffusion controlled and, as a consequence, slow.

Low Temperature Growth of Pb(Zr,Ti)O 3 Thin Films by Two Step MOCVD Using Seeds

Perovskite Pb(Zr,Ti)O 3 (PZT) thin films were successfully obtained at 395°C by metalorganic chemical vapor deposition (MOCVD) using seeds. In our MOCVD, prior to the growth of PZT films, PbTiO 3 or PZT was deposited as a seed. PZT thin films with seeds showed better crystalline structure and ferroelectric properties than those PZT films without seeds. Seeded PZT films showed 2Pr of 8.7∼17.3 w C/cm 2 and 2Ec of 70∼180kV/cm. Seed effect on the ferroelectric properties of Ti rich PZT films was larger than that of Zr rich PZT films.

Ferroelectric characteristics of oriented Pb(Zr1−xTix)O3 films

Pb 1.2 Zr 1−x Ti x ) O 3 (PZT) films with a variety of compositions were prepared by spin coating on Pt/Ti/SiO2/Si substrate with sol–gel processing. The roles of composition (phase) and orientation in ferroelectric properties of PZT films have been determined. The Zr-rich PZT films with (111)-oriented PZT films have a higher remanent polarization but also show a higher fatigue rate as compared to (100)-oriented films in both Zr-rich(65/35) and Ti-rich(35/65) PZT compositions. The lower fatigue rate of (100)-oriented film can be attributed to its easier reversible domain-wall motions compared to (111)-oriented PZT films due to the absence of internal field stress and less dependence on electrical field. A mode based on domain-wall contribution instead of film–electrode interface is favored to elucidate the role of orientation in fatigue characteristics of PZT films.

Effect of Glass Composition on Chemical Reaction between Lead Zirconate Titanate and Glasses. (Part 2). Lead-silicate and Lead-borosilicate Glasses.

The products of reaction between Pb(Zr0.53Ti0.47)O3 (PZT) and glasses in the PbO-SiO2 and PbO-B2O3-SiO2 systems at 850°C were studied using powder and bulk PZT samples. A reaction zone was formed between bulk PZT and the glass. The microstructure of the reaction zone changed with the amount of PZT dissolved in the glass phase, which was dependent on the activity of PbO in both the glass phase and PZT. When the amount of dissolved PZT was small, as in the reaction between PZT and 60mol% PbO⋅40mol% SiO2 glass, the glass phase penetrated into grain boundaries of PZT, and no solid reaction product was formed. When the amount of dissolved PZT was intermediate, as in that between PZT and 40mol% PbO⋅60mol% SiO2 glass, the glass phase penetrated into the PZT pellet and ZrO2 particles were precipitated in the glass phase. When the amount of dissolved PZT was large, as in those between PZT and 60mol% PbO⋅20mol% B2O3⋅20mol% SiO2 glass and 40mol% PbO⋅30mol% B2O3⋅30mol% SiO2 glass, the reaction zone was formed, which was composed of Ti-rich PZT and ZrO2 particles dispersed in the glass phase.

The effect of excess Pb content on the crystallization and electrical properties in sol–gel derived Pb (Zr 0.4Ti 0.6)O 3 thin films

The crystallization behavior and electrical properties are closely related to the excess Pb content in PZT (Zr/Ti=40/60) thin films. However, the role of excess Pb in the crystalline growth has not been precisely defined. In this work, the effect of excess Pb content on the crystallization and ferroelectric properties of these films was investigated. To analyze the effect, PZT films containing various amounts of excess Pb, but with same grain size and film orientation, were prepared. In the case of films derived from PZT solutions with a high excess-Pb content, more nuclei formed, but grew into smaller-sized grains than in the case of films with a low Pb content. On the other hand, a conversion from (100)- to (111)-preferred orientation was observed as a result of time-dependent bi-orientational growth. A depth profile analysis using Auger electron spectroscopy revealed that excess Pb enhanced the formation of Ti-rich PZT at the Pt/PZT interface. This Ti-rich PZT seemed to be the origin of the (111) orientation in the film with high excess Pb content. As higher excess Pb was included, the films showed a higher permittivity, a lower distribution of the space charge layer and better resistance against repeating fatigue cycles, due to the inhibition of movement of vacancies. These phenomena could be applied to the formation of a space charge layer via oxygen vacancy accumulation in the case of films with a low Pb content.

Enhanced Fatigue Property through the Control of Interfacial Layer in Pt/PZT/Pt Structure

Ferroelectric Pb(ZrxTi1-x)O3 PZT thin film capacitors with Pt(111)/SiO2/Si substrate were fabricated by sol-gel method. Ultrathin PZT layer containing various contents of excess Pb was adopted as an interfacial layer to investigate the role of excess Pb on the formation of interfacial region between PZT film and Pt bottom electrode. An improvement of electrical properties was observed according to the content of excess Pb in interfacial PZT layer due to the inhibition of inter-diffusion at film-substrate interface as well as defect formation. The formation of Ti-rich PZT at the initial stage of anneal due to excess Pb was responsible for the excellent ferroelectric characteristic. This implied that the role of excess Pb in film-substrate interface was of significance to the long-term reliability.

Effect of Glass Composition on Chemical Reaction between Lead Zirconate Titanate and Glasses. (Part 1). Lead-Borate Glasses.

The products of reaction between Pb(Zr0.53Ti0.47)O3 (PZT) and PbO-B2O3 glasses at 850°C were studied using powder and bulk PZT samples. PZT dissolved in glass phase and solid products were precipitated. The reaction zone composed of glass phase and solid products was formed between bulk PZT and glass. As the B2O3 content in the glass increased, the amount of dissolved PZT and the thickness of reaction zone increased. When glasses with 40 and 60mol% B2O3 were used, the solid products were Ti-rich PZT and ZrO2 (ZrO2-TiO2 solid solution), which were expected from the phase diagram of the PbO-ZrO2-TiO2 system. When a glass with 80mol% B2O3 was used, the solid products were ZrO2 and TiO2, which were supposed to be formed by non-equilibrium reaction sequences. The microstructure of the reaction zone depended on the chemical composition of glass, indicating that the solubility of constituent oxides of PZT was dependent on glass composition.

Domain structure and electrical properties of highly textured PbZrxTi1−xO3 thin films grown on LaNiO3-electrode-buffered Si by metalorganic chemical vapor deposition

Thin films of highly (100) textured fine-grain (lateral grain size ≅0.1 to 0.15 μm) PbZrxTi1−xO3 (PZT) (x = 0 to 0.7) were grown on conductive perovskite LaNiO3-buffered platinized Si substrates by metalorganic chemical vapor deposition. Domain configuration and crystalline orientation were studied using x-ray diffraction and transmission electron microscopy. The predominant domain boundaries of Ti-rich tetragonal-phase PZT and Zr-rich rhombohedral-phase PZT were found to be on the (110) planes and (100) planes, respectively. The equilibrium domain widths were observed and estimated numerically on the basis of transformation strain, grain size, and domain boundary energy. The peak value of the dielectric constant was 790 near the morphotropic boundary. Hysteresis behavior of these PZT thin films was demonstrated. A decrease in coercive field with the increment of Zr content was found; this variation was attributed to domain density and the multiplicity of polarization axes. Furthermore, the low leakage current (J ≤ 5 × 10−7 A/cm2 at V = 4 V) was observed for all samples, and the involvement of several possible conduction mechanisms was suggested.

Absorption-Reflection Infrared Spectroscopy Studies of Sol-Gel Prepared Ferroelectric Pb(Zr,Ti)O3 Thin Films on Pt Electrodes

Although the sol-gel method is ideally suited for the preparation of ferroelectric PZT thin films, poor reproducibility and the need to lower crystallization temperatures remain an issue. To address these problems, we have studied the mechanism of thin film formation using absorption-reflection infrared spectroscopy for a novel and less harmful precursor solution system based on butoxyethanol. By recording in situ infrared spectra we were able to monitor hydrolysis, condensation, decomposition and crystallization phenomena versus temperature. We speculate that the lower reactivity of butoxyethanol is responsible for the higher quality of Ti rich PZT based ferroelectric capacitors prepared by a butoxyethanol precursor solution compared with the more widely used methoxyethanol one. Finally, we observed that film's decomposition kinetics is faster as compared to bulk samples and depends on film thickness and electrode layer.

Comparative Role of Metal-Organic Decomposition-Derived [100] and [111] in Electrical Properties of Pb(Zr, Ti)O3 Thin Films

The effect of composition (phase), texture, microstructure and thickness on electrical properties of Pb(Zr1-x Tix )O3 (PZT) films have been evaluated. Zr-rich PZT films with [111] texture have a higher remanent polarization and dielectric constant, but a lower coercive field as compared with PZT[100] films. Ti-rich PZT films with [100] texture have a higher dielectric constant, but a lower remanent polarizalion and coercive field as compared with PZT[111] films. Near the morphotropic phase boundary (MPB) composition, films with a mixed texture of [111] and [100] have a higher dielectric constant than PZT[100] and PZT[111] films even though the values of remanent polarization and coercive field of the mixed textured films are in between those of the other two films. Both remanent and saturation polarization are independent of film thickness, whereas dielectric constant decreases but coercive field increases at very small thickness.