Lead Zirconate Titanate Thin Films by Aerosol Plasma Deposition: Microstructure Analysis

Lead zirconate titanate (Pb(Zr,Ti)O₃, PZT) thin films were grown on silicon 〈100〉 substrate by aerosol plasma deposition (APD) using solid-state-reacted powder containing donor oxide Nb₂O₅ when keeping the substrate at room temperature and 200°C. Crystalline phases of the deposited films have been analyzed via X-ray diffractometry (XRD), and microstructure via scanning and transmission electron microscopy (SEM and TEM). Cross-sectional TEM revealed that the microstructure comprised several layers including the deposited PZT film and the platinum-electrode-and-titanium-buffered layers on SiO₂–Si substrate. The Pt-electrode layer contained (111)_Pt twinned columnar grains with a slight misorientation and forming low-angle grain boundaries among them. The PZT layer contained randomly oriented grains embedded in an amorphous matrix. Some of the PZT grains, oriented with the zone axis Z = [[Twomacr]11]_PZT parallel to Z = [111]_Pt, were grown epitaxially on the Pt layer by sharing the (111)_PZT plane with the (111)_Pt twinned columnar Pt crystals. However, the existence of such an orientation relationship was confined to several nanosize grains at and near the PZT-Pt interface, and no gross film texture has been developed. An amorphous grain boundary phase, generated by pressure-induced amorphisation (PIA) in the solid state, was identified by high-resolution imaging. Its presence is taken to account for the densification of the PZT thin films via a sintering mechanism involving an amorphous phase on deposition at 25° and 200°C.     

Abnormal Grain Growth of Pb(Mg1/3Nb2/3)O3-35 mol% PbTiO3 Ceramics Induced by the Penetration Twin

Pb(Mg_1/3Nb_2/3)O₃-35 mol% PbTiO₃ (PMN-35PT) specimens with a 5 mol% excess PbO were prepared by excessive heat treatment at 1150°C to induce abnormal grain growth. Through electron backscatter diffraction analysis and the observation of a three-dimensional morphology, the abnormally grown PMN-35PT grains were found to be twinned crystals with penetration characteristics. The morphology of the PMN-35PT twinned crystal was crystallographically analyzed. The abnormal grain growth of PMN-35PT is suggested to be due to preferential growth at the reentrant angles formed by twins.     

Sintering Model for Mixed-Oxide-Derived Lead Zirconate Titanate Ceramics

The properties of lead zirconate titanate (PZT) ceramics are determined by the microstructure and chemical homogeneity of Zr, Ti, and dopants within the grains as well as the presence of secondary grain boundary phases. Stoichiometric 53/47 PZT and compositions with 3 mol% PbO excess were prepared by the mixed-oxide process, and were densified by pressureless sintering in oxygen. The influence of PbO content and different La concentrations on the densification behavior was analyzed by dilatometric measurements. Quantitative image analysis showed a different relative density and grain size dependence for samples containing >0.5 mol% additives compared to samples with <0.5 mol% La. On the basis of a model experiment and by using different analytical methods (microprobe analysis, HRTEM, STEM, and Auger spectroscopy) three types of inhomogeneities could be detected in conventionally prepared PZT ceramics: the existence of Ti and La enrichment in the core of PZT grains, and PbO-rich secondary phases in triple junctions as well as in grain boundary films. The results of the microstructural characterization and the analysis of the densification behavior were finally combined to deduce a sintering model based on a Pb-vacancy concentration gradient within the PZT grains.     

Seeded Growth from Twinned and Untwinned Abnormal Grains of Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 in a Matrix Containing PbO Additions

The growth of abnormal grains of PMN–35PT containing Σ3 twin boundaries was compared with that of untwinned abnormal grains of PMN–35PT. It was thought that the twinned abnormal grains might have a growth advantage because of the presence of reentrant edges. The aforementioned types of grains were embedded in a PMN–35PT polycrystalline matrix with 3 vol% excess PbO, and grown by annealing in an oxygen atmosphere at 1150°C for varying times. It was found that abnormal grains containing Σ3 boundaries showed a comparable degree of growth to that of the untwinned grains. Furthermore, for the twinned seed crystals, the extent of growth was independent of whether there was any initial entrapped porosity within the abnormal grain.     

Electric-Field-Induced Crack Growth Behavior in PZT/Al2O3 Composites

Hard lead zirconate titanate (PZT) and PZT/Al₂O₃ composites were prepared and the alternating-electric-field-induced crack growth behavior of a precrack above the coercive field was evaluated via optical and scanning electron microscopy. The crack extension in the 1.0 vol% Al₂O₃ composite was significantly smaller than that in monolithic PZT and the 0.5 vol% Al₂O₃ composite. Secondary-phase Al₂O₃ dispersoids were found both at grain boundaries and within grains in the composites. A large number of dispersoids were observed at the grain boundaries in the 1.0 vol% Al₂O₃ composite. It appears that the Al₂O₃ dispersoids reinforce the grain boundaries of the PZT matrix as well as act as effective pins against microcrack propagation.     

Effect of the synthesis conditions on the properties of polycrystalline films of lead zirconate titanate of nonstoichiometric composition

The model representations of the formation of the internal fields at the grain boundaries in polycrystalline lead zirconate titanate (PZT) films are discussed. According to the model proposed, the local distortion of the stoichiometric composition of the PZT films caused by the segregation of the oxygen and lead ions from the bulk PZT grains towards their boundaries during high-temperature annealing gives rise to electrical double layers near the grain boundaries and fixes the polarization in these areas. As a result, the ferroelectric polarization that can be switched by the electric field in polycrystalline PZT films decreases.     

Grain-Size Dependence of Electrically Induced Microcracking in Ferroelectric Ceramics

A high dc field (1 and 3 kV / mm) was applied to BaTiO₃ and PZT ceramics, electrically induced microcracks occur at the grain boundaries and propagate into the grains. The number of cracks becomes larger with increasing grain size and poling field.     

Faceting of High-Angle Grain Boundaries in Titanium-Excess BaTiO3

The grain boundaries in BaTiO₃ with excess Ti of 0.5, 0.3, and 0.1 at.% sintered at 1300° or 1250°C have been examined by scanning electron microscopy (SEM), electron backscattered diffraction pattern (EBSP), and transmission electron microscopy (TEM). In the 0.1% Ti-excess specimen, large grains growing abnormally form high-angle grain boundaries when they impinge on each other as verified by EBSP. A large fraction of these grain boundaries are faceted with hill-and-valley shapes. In the 0.5% Ti-excess specimen, large grains growing abnormally are elongated in the directions of their {111} double twins. These grains often form flat grain boundaries parallel to their {111} planes with the fine matrix grains, and the grain-boundary segments between the large impinging grains with high misorientation angles are often also parallel to the {111} planes of one of the grains. These grain boundaries are expected to be singular. Most of the grain boundaries between the randomly oriented fine-matrix grains in the 0.3 at.% Ti-excess specimen are also faceted with hill-and-valley shapes at finer scales when observed under TEM. The facet planes are parallel to {111}, {011}, and {012} planes of one of the grain pairs and are also expected to be singular. These high-angle grain boundaries lying on low index planes of one of the grain pairs are similar to those observed in other oxides and metals.     

Ultra-precision grinding of AlON ceramics: Surface finish and mechanisms

Aluminum oxynitride (AlON) can be effectively finished by ultra-precision grinding. In this work, the ultra-precision grinding experiment was conducted on AlON to investigate surface characteristics and material removal mechanism. The ground surface has an unusual non-uniform morphology resulted from the different material removal modes. Grazing incidence X-ray diffraction (GIXRD), nanoindentation and Electron Back-Scattered Diffraction (EBSD) were carried out to study the micro-properties of AlON. The results revealed that the micro mechanical properties vary with the grain orientation on the surface. The morphologies of ground surface are consistent in the twinned grains and change with the grain orientation. By comparing the relationship of machining size and grain size, the material removal modes of individual grains should be taken into consideration during ultra-precision grinding. Based on this, a simple theoretical model was proposed to explain the material removal mechanism of AlON under ultra-precision grinding.     

Poling behaviour at the grain boundaries of ferroelectric PZT thin films investigated by electric scanning force microscopy

The poling behaviour of PZT(53/47) films was investigated separately at the grain boundaries and inside the grain volumes by ESFM. The films were prepared by sol-gel processing on Pt-metallized polycrystalline Al₂O₃, substrates and consisted of columnar grains with mean diameter of 220 nm. It was found that the polarization was decreased at simple grain boundaries in a border zone of 20 nm to 40 nm width, with up to 42% related to the grain volumes. At triple points, the polarization was decreased by the same amount in a border zone of 40 nm to 80 nm width with respect to the grain volumes. An asymmetric poling behaviour of the saturation polarization was found at the grain boundaries. The switchable polarization of the grain boundaries was determined to be 74% of that of the grain volumes. The coercive field was clearly increased at the grain boundaries.     

Effect of sintering temperature on the secondary abnormal grain growth of BaTiO3

When BaTiO₃ specimens containing a small amount of excess TiO₂ were sintered for more than 15 h, some grains grew abnormally to several millimeters in size. This phenomenon may be referred to as the secondary abnormal grain growth (SAGG) because it occurred from a large and uniform grain structure (average grain size: 70 μm) after completion of primary abnormal grain growth. SAGG was observed only at a very narrow temperature range between 1360 and 1370°C, where the solid–liquid interface structure was atomically smooth. Almost all the secondary abnormal grains contained the (111) double twin, which provides the persistent twin-plane re-entrant edge (TPRE). During SAGG, the growth of matrix grains was strongly suppressed and material transfer occurred preferentially to the grains with a (111) double twin.     

Sintering and Piezoelectric Properties of Co-Fired Lead Zirconate Titanate/Ag Composites

Lead zirconate titanate (PZT) ceramics were co-fired with pure Ag powders at 1200°C for 1 h, and the ferroelectric and piezoelectric properties of the resultant PZT/Ag composites were evaluated, aimed at potential applications in functionally graded piezoelectric actuators with enhanced mechanical reliabilities. In the range of 1–15 vol% Ag concentration, pure Ag powder remained as the second phase in the composites, and a small quantity of Ag entered into the crystal lattice of PZT and slightly increased the lattice constants of a and c . The Ag powders were found to aggregate together and grow to larger particles in the composites. The ceramic grains grew from an initial size of 1.5 μm for monolithic PZT to 2.5 μm for the PZT/Ag composites, and the grain size was almost the same for various Ag concentrations. It was found that the ferroelectric and piezoelectric properties decreased when Ag was added to PZT. In the range of 1–15 vol% Ag concentration, the remanent polarization P _r decreased from 38 to 27 μC/cm², the piezoelectric constant d ₃₃ decreased from 394 to 105 pC/N, and the planar electromechanical coupling factor k _p decreased from 0.69 to 0.15, respectively. These piezoelectric properties of the present PZT/Ag composites were compared with the results reported for PZT/Pt composites, and discussed in relation to microstructural features.     

Grain Growth and Twin Formation in 0.74PMN·0.26PT

The mechanisms controlling normal and exaggerated grain growth in lead magnesium niobate–lead titanate (PMN–PT) ceramics have been investigated by varying the PbO-based liquid-phase volume fraction from 0.03 to 0.6 and sintering temperature from 900° to 1100°C. There is a transition in matrix grain growth rate and matrix grain shape with liquid fraction; samples with liquid volume fractions less than ∼0.15 show relatively small equiaxed grains resulting from grain-to-grain impingement. Samples with higher liquid fractions show significantly larger, facetted, cube-shaped grains, whose size is independent of liquid fraction, indicating that a surface nucleation rate mechanism controls growth in this regime. Exaggerated grains were found in the high liquid fraction samples. Electron backscatter diffraction showed that all of the exaggerated grains contained 60°〈111〉 twins but none of the normal matrix grains contained twins. The reentrant angles in the twinned grains give them a growth advantage over untwinned grains, resulting in a population of exaggerated grains.     

金属有机物热分解法合成的PZT纳米晶粉末的表征

以醋酸铅、庚酸氧锆和钛酸丁酯为原料,采用金属有机物热分解法成功地制备了ＰＺＴ钠米晶粉末,并通过ＸＲＤ,ＦＴＩＲ,ＤＴＡ,Ｒａｍａｎ,ＴＥＭ等方法对钠米粉末的结构进行了表征。粉末粒径为２０－４０ｎｍ,大小均匀,颗粒呈球形,且分散性好。研究结果显示,金属有机物热分解法是制备ＰＺＴ或其它纳米粉末的一种很有前途的方法。     

Fully Dense, Fine-Grained, Doped Zinc Oxide Varistors with Improved Nonlinear Properties by Thermal Processing Optimization

Fully dense, doped ZnO varistors were prepared using an easy two-stage pressureless-sintering method at temperatures as low as 825°C, with a grain size of ∼0.5 μm. After the highly nonohmic ZnO varistors were sintered, their fine microstructure consisted of uniformly sized grains, small spinel grains with partially dissolved manganese and cobalt oxides discontinuously distributed in the fairly wide grain boundaries, and an intergranular layer of bismuth-rich crystalline phase mainly detected at three or four ZnO grain junctions. There were twins near the middle of almost all the ZnO grains. The abnormally high nonlinear properties of the almost nanostructured varistors ( F _B≈ 6–8 kV/mm and α= 270) were attributed to a uniform and very fine microstructure, a high ZnO–ZnO grain direct contacts concentration, and a uniform hybrid layer substructure (grain boundaries and twin boundaries) with different (but probably accumulative) potential barriers.     

Growth of BaTiO3 Seed Grains by the Twin-Plane Reentrant Edge Mechanism

Two different types of BaTiO₃ seed particles, normal and twinned seeds of ∼30 μm on the average, were prepared from crushed sintered specimens. Normal seeds were obtained from the usual BaTiO₃ sintered compacts, while twinned seeds containing a double twin were obtained from BaTiO₃ compacts sintered with 2 mol% of SiO₂. The BaTiO₃ powder compacts were again prepared with 5 wt% of seed grains and sintered under various conditions. The microstructural evolution was quite different in the two cases: the growth of normal seed grains was ultimately limited but that of the twinned seeds continued extensively. The observed difference is discussed in terms of the growth mechanism and the atomic structure of interfaces.     

Shape Dependence of the Coarsening Behavior of Niobium Carbide Grains Dispersed in a Liquid Iron Matrix

In niobium carbide–iron (NbC-Fe) specimens where the grains were faceted, abnormally large grains appeared during coarsening. Normal and uniform grain growth occurred when the grain shape was changed to a spherical morphology by the addition of a small amount of boron. The results have been discussed, in terms of a coarsening mechanism, depending on the atomic structure of the interface. For faceted grains with an atomically smooth interface structure, the coarsening was suggested to occur via two-dimensional nucleation and a lateral-growth mechanism. For spherical grains with an atomically rough interfacial structure, diffusion was suggested to control the coarsening process.     

Adhesion of Electrolessly Deposited Nickel on Lead Zirconate Titanate Ceramic

The adhesion of electrolessly deposited Ni onto lead zirconate titanate (PZT) ceramic has been measured as a function of both the ceramics surface preparation prior to metalization and the plated Ni thickness. A maximum in NI/PZT interfacial adhesion of approximately 27 kg/cm², as measured by a pull test, occurs when the ceramic grain boundaries are chemically etched, thereby providing points to mechanically anchor the Ni deposit. The adhesion decreases with overetching as the ceramic grains are undercut and drops off dramatically with increasing plated Ni thickness.     

Mobility transition at grain boundaries in two‐step sintered 8 mol% yttria‐stabilized zirconia

Stagnation of grain growth is often attributed to impurity segregation, which becomes more severe as the grain size grows. In this respect, there is no evidence for segregation‐induced slowdown in the grain growth of yttria‐stabilized cubic zirconia, which obeys the parabolic law when the size increases by more than ten times. However, lowering the temperature below 1300°C triggers an abrupt slowdown, constraining the average grains to grow by less than 0.5 μm in 1000 hours despite a relatively large driving force imparted in the fine grains of ~0.5 μm. Yet isolated pockets of abnormally large grains, and even most remarkably, pockets of abnormally small grains, emerge in the same latter sample. Such extreme bifurcation of microstructure has never been observed before, and can be explained by an inhomogeneous distribution of immobile four‐grain junctions. The implications of these findings for two‐step sintering are discussed.     

PZT-cobalt ferrite particulate composites: Densification and lead loss controlled by quite-fast sintering

During densification at 1100–1200 °C of particulate lead zirconate titanate (PZT)/cobalt ferrite (CF, 26–81  mol%) composites, side reactions do occur that are detrimental to the properties of the so-obtained material. Such reactions are promoted by initial PbO loss, the extent of which can be determined by means of XRD analysis of the densified samples taking into account the amount of ZrO₂ and the variations of the perovskite’s tetragonality. In this process, titania is produced which reacts with CF to form cobalt titanate. Microstructural characterization showed that CF grain size distribution can be mono- or bi-modal, and CF overgrowth was found to affect the coercivity of the material. In the case of the PZT:CF 74:26 composites, full densification and prevention of unwanted side reactions were achieved by designing a quite-fast sintering process. The high coercivity (789 Oe) displayed by these composites is related to the good dispersion of 250 nm euhedral CF grains in the PZT matrix and limited PZT grain growth (240 nm).