In situ measurement of material properties of lead zirconate titanate piezoelectric ceramics during cyclic mechanical loading

To better understand the material properties of lead zirconate titanate (PZT) ceramics, in situ mechanical and electrical properties have been investigated continuously during cyclic mechanical loading. The material properties are demonstrated to change as a function of applied maximum stress, with the effective elastic constant increasing with increase of the stress level. The increase of effective elastic constant is attributed to the domain structure of the PZT. 90° domain switching can occur anywhere in the sample, which makes the strain accumulate and leads to high values of the effective elastic constant. The domain switching characteristics are clearly revealed by electron back scattered diffraction analysis. The changes of the electrical properties (electromechanical coupling coefficient, piezoelectric constant and permittivity) are in the opposite sense because of the material strain (or material damage), caused by the change of domain orientation; the electrical properties are degraded with increasing cycle number and applied stress. Based upon the variation of the material properties, details of the damage characteristics in the PZT ceramics are discussed.     

Domain switching characteristics of lead zirconate titanate piezoelectric ceramics during mechanical compressive loading

To better understand the domain switching characteristics of lead zirconate titanate (PZT) ceramics, the orientations of domains have been directly investigated during loading and unloading using various experimental techniques. Upon loading, linear and non-linear fracture mechanics of the PZT ceramics are observed. The slope of the stress–strain response is attributed mainly to lattice strain and domain switching strain. During the loading process, electrical activity also occurs several times in the PZT ceramics. This activity is related to a lightning-like phenomenon and consists of a bright flash with a click. This electrogenerative event is caused by severe domain switching. The characteristics of domain switching and reverse switching are detected during the loading and unloading processes. The amount of domain switching depends on the grain, due to different stress levels. In addition, two patterns of 90° domain switching systems are characterized, namely (i) 90° turn about the tetragonal c-axis and (ii) 90° rotation of the tetragonal a-axis.     

Mechanically controlled domain structure in PZT piezoelectric ceramics

The influence of the mechanically applied load on the piezoelectric properties and domain switching characteristics has been investigated experimentally using a soft lead zirconate titanate (PZT) piezoceramic, which de-poled to make randomly orientated domain structures. Mechanical loads were applied to rectangular PZT ceramics under compressive and tensile stresses. With the applied stress, 90° domain switching occurred in many locations in the PZT ceramics, where the higher stress caused more severe domain switching. The domain switching occurred with different directions, depending on the stress direction. For instance, the (2 0 0) peak increased and the (0 0 2) peak decreased when more severe compressive stress was applied. The opposite trend was detected as more severe tensile stress was applied; the (2 0 0) peak decreased and the (0 0 2) peak increased. With the applied loading process, the domains (long tetragonal c-axis) were orientated regularly in the PZT ceramics. Furthermore, like the electrically poled PZT ceramics, the domain orientations were more aligned when the sample surfaces were constrained during the loading process.     

Correlation between Surface Texture and Chemical Composition in Undoped, Hard, and Soft Piezoelectric PZT Ceramics

The electrical and mechanical properties of piezoelectric lead zirconate titanate (PZT) ceramics are strongly influenced by domain-wall motion, which can be tailored via the substitution of ions within the perovskite structure. Different domain mobilities are achieved by lead and/or oxygen vacancies, according to the valency and ionic radius of the dopants. To quantify the surface near domain mobility, hard (silver-doped), soft (lanthanum-doped), and undoped PZT ceramics have been prepared. An applied mechanical stress after sintering causes texturing near the surface, because of the ferroelastic behavior of the 90° domains. The texture is quantified via X-ray diffractometry (XRD) analysis of the tetragonal F _T(002)- and F _T(200)-peak intensities, using least-squares refinement with Gaussian profile functions. The samples are subsequently annealed to remove the surface texture and again characterized via XRD measurements. However, annealed samples still reveal a preferred domain orientation that can be removed only by a second annealing of the pulverized samples. A comparison of the tetragonal additive systems clearly reveals the greatest domain mobility for lanthanum-doped PZT ceramics, whereas the silver-doped and undoped samples have similar ferroelastic behavior. Furthermore, the surface texture of all the compositions is dependent on the applied mechanical stress and cannot be removed completely by heat treatment.     

Effects of 90° domain switching on electric generation properties of PZT ceramic

The influence of domain switching on the electric generation properties of lead zirconate tinatate (PZT) ceramic has been investigated after static and cyclic loadings under various conditions. A PZT ceramic of size ϕ8.0 mm×0.17 mm, consisting of a tetragonal lattice structure, i.e., c/a≠1.014, was used. Domain switching occurred as a result of the applied stress, where three different switching modes were employed: (I) simple 90° switching; (II) 90° switching with 90° rotation; and (III) 90° switching with 180° rotation. The rates of the switching mode were different: the simple switching mode (Mode I) was 20%; and both complicated switching modes (Mode II and III) were 40%. The extent of 90° domain switching was different depending on the grain and where the direction of the tetragonal structure (c-axis direction) was affected, e.g., the closer the parallel between the c-axis and the stress direction, the stronger the domain switching. The electric generation voltage increased with increasing applied cyclic stress; however, that voltage dropped suddenly as the stress value was close to its elastic limit. This is due to the 90° domain switching. Such domain switching (reduction of the electric voltage) occurred in the early cyclic stage.     

Fracture Mechanisms in Ferroelectric-Ferroelastic Lead Zirconate Titanate (Zr: Ti=0.54:0.46) Ceramics

Fracture toughness, K _IC, of a single-phase commercial lead zirconate titanate (PZT) ceramic (Zr/Ti=0.54/0.46) of tetragonal structure ( c/a =1.019) was measured using the single edge notched beam method above and below the Curie temperature. Domain switching (poling) under electrical and mechanical loading was examined using X-ray diffraction. Surface grinding, electrical poling, and mechanical poling caused crystallographic texture. Similar texture, indicative of domain switching, was also observed on fracture surfaces of some saples fractured at room temperature. At room temperature, the highest K _IC measured was 1.85 MPa·m^1/2, while above the Curie temperature it was about 1.0 MPa·m^1/2. Cracks emanating from Vickers indents in poled samples were different in the poling and the transverse directions. The difference in crack sizes is explained on the basis of domain switching during crack growth. These results indicate that ferroelastic domain switching (twinning) is a viable toughening mechanism in the PZT materials tested.     

Domain switching characteristics of lead zirconate titanate piezoelectric ceramics on a nanoscopic scale

Domain switching characteristics of lead zirconate titanate ceramics with and without poling under compressive loading are investigated using electron backscatter diffraction. For loading in the poling direction, the switching strain is stronger than that for loading perpendicular to the poling direction. There is strong domain switching when the domain (c-axis of the tetragonal structure) is orientated close to the loading direction. A large number of domains are switched between 85.4° and 90.0°, with many crossing the loading axis. Each grain consists of domains with three different patterns; i.e., with c-axis orientated in three directions in each grain. The patterns remain unchanged even with domain switching and strong deformation. However, the ratios among the patterns depend on compressive stress. Under stress, one or two specific domain modes are switched to about 90°, although others are not switched as much. These domain switching characteristics are related to the poling and loading directions. 90° domain switching model is proposed on the basis of twin deformation model. Due to the aspect ratio of c/a = 1.014 (tetragonal structure), the angle of the switching is less than 90° (89.2°). This angle is corresponding to the switching angle obtained by an electron backscatter diffraction analysis (Ave. 88.9°).     

Effect of Nb and K doping on the crack propagation behaviour of lead zirconate titanate ceramics

In the present study, we investigated the effect of doping on the crack propagation behaviour of lead zirconate titanate ceramics (PZT), particularly crack growth resistance and slow crack growth. Three PZT grades were processed: an undoped PZT, a soft PZT doped with niobium, PNZT, and a hard PZT doped with potassium, PKZT. The composition was chosen close to that of the morphotropic phase boundary (MPB), known to give excellent electromechanical properties. The soft material showed an important crack growth resistance and its slow crack growth curve V–K_I (crack velocity versus stress intensity factor, K_I) is shifted toward higher values of K_I. The results are discussed in terms of toughening due to ferroelastic domain switching under mechanical loading.     

A study of the effects of vibration on the electric power generation properties of lead zirconate titanate piezoelectric ceramic

To better understand how the electric power generated from PZT piezoelectric ceramics is affected by mechanical loading conditions the power generation was examined during cyclic loading under various loading conditions. The electric power generation was continuously examined using a monitoring system that we have recently developed. This system revealed that the electric power increased with increase of the applied load but then decreased when the applied load exceeded a certain level. In addition, greater electric power was generated with a simple beam configuration compared with a cantilevered beam. The change of electric power generation was directly related to the stress direction; high stress in the tetragonal structure parallel to the c-axis gave rise to high electric power generation. On the other hand, material failure, including domain switching and crack generation, caused a reduction of the electric power generated. Based upon our experimental data, suitable loading conditions to give high piezoelectric energy generation have been clarified.     

Phase Stability and Ferroelectric Properties of Lead Strontium Zirconate Titanate Ceramics

The effect of compositional modifications on the field-induced phase-transition behavior and dielectric properties of strontium-doped lead zirconate titanate (PZT) ceramics was studied. PZT compositions with different strontium and titanium contents, within the general formula Pb_{1– x} Sr _x (Zr_{1– y} Ti _y )O₃ and located in the tetragonal antiferroelectric (AFE) and rhombohedral ferroelectric (FE) phase fields were prepared by tape casting and sintering. X-ray diffraction and polarization measurements were used to locate compositions suitable for investigation of the field-induced AFE–FE phase transition. The results indicated that a higher Sr²⁺ content decreased the polarization and hysteresis and increased the switching field; a lower Ti⁴⁺ content decreased the polarization and increased the switching field and hysteresis. A high room-temperature dielectric constant was obtained for compositions near the phase boundary. These results suggest that a combination of both A -site and B -site modifications can be used to tailor ferroelectric properties, such as the switching field and hysteresis, of these strontium-doped PZTs displaying a field-induced AFE–FE phase transition.     

Microstructure,electrical and mechanical properties of MgO nanoparticles-reinforced porous PZT 95/5 ferroelectric ceramics

Porous Pb (Zr_0.95Ti_0.05) O₃/xMgO (PZT/MgO, x=0, 0.1, 0.2, 0.5 and 1.0 wt%) ferroelectric ceramics were prepared with MgO nanoparticles as reinforcing phase. The effects of MgO nanoparticles on the phase, microstructure, electrical and mechanical properties of as-prepared ceramics were investigated. The results show that the grain size is reduced obviously when increasing the amount of MgO. Compared with pure porous PZT, T_C of MgO-added PZT ceramics shifts to higher temperature. Moreover, dielectric, ferroelectric and piezoelectric properties show no much degradation. Further, PZT/MgO ceramics possess enhanced mechanical properties compared to pure porous PZT ceramics, the largest increment of the fracture toughness and hardness being 31.3% and 19.8%, respectively. The optimal electrical and mechanical properties are obtained with the addition of less than 0.5 wt% MgO nanoparticles.     

Microstructure and electric properties of Pr-doped Pb(Zr0.52Ti0.48)O3 ceramics

Improving the piezoelectric activity of lead zirconate titanate (PZT) ceramics is of great importance for practical applications. In this study, the influence of Pr³⁺ doping on the ferroelectric phase composition, microstructure, and electric properties on the A-site of (Pb_1-1.5xPr_x)(Zr_0.52Ti_0.48)O₃ is extensively investigated. A dense and fine microstructural sample is obtained with the introduction of Pr³⁺. The results show that the morphotropic phase boundary (MPB) moves to the rhombohedral phase region. The rhombohedral and tetragonal phases exhibit an ideal coexistence in the 4 mol.% Pr³⁺ doped (PPZT4) samples. Lead vacancy and the reduction of the potential energy barrier are considered to be the key mechanisms for donor doping, which is upheld by the Pr³⁺ doping. Combining the I-E hysteresis loops with the P-E hysteresis loops, it becomes apparent that both contribution maximums of the domain switching and residual polarisation are in PPZT4. Moreover, the thermal aging resistance of PZT is improved by doping, and the temperature stability is optimised from 83% in PZT to 96% in PPZT4. Hence, an appropriate amount of Pr³⁺ doping can effectively improve the piezoelectric activity of PZT ceramics in the MPB area and optimise the performance stability of the material under application temperatures.     

Higher permittivity of Ni-doped lead zirconate titanate,Pb[(Zr0.52Ti0.48)(1-x) Nix]O3, ceramics

The paper reports highest obtained dielectric constant for Ni-doped Lead Zirconate Titanate [PZT, Pb(Zr_0.52Ti_0.48)O₃] ceramics. The Ni-doped PZT ceramic pellets were prepared via conventional solid-state reaction method with Ni content chosen in the range 0–20?at%. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were employed to investigate the crystal structure of the prepared ceramics. The X-ray diffraction analysis indicated that the ceramic pellets had crystallized into tetragonal perovskite structure. A minute displacement of XRD peaks was detected in the diffraction spectra of Ni-doped PZT ceramic samples which when examined by size-strain plot (SSP) method revealed presence of homogenous strain that decreased with increase in concentration of Ni. In FTIR the maximum absorption at 597?cm^?1, 608?cm^?1, 611?cm^?1, 605 and 613?cm^?1 for Ni?=?0, 5, 10, 15 and 20?at%, respectively, confirmed the formation of perovskite structure in all the compositions and the slight shift suggests decrease in cell size on doping. The values of dielectric constant (ε′) & tanδ as a function of frequency and temperature were measured for the prepared ceramics and it revealed highest ever reported dielectric constant for Ni - doped PZT with Ni?=?5?at%. The dielectric variation with temperature exhibited a diffused type ferroelectric–paraelectric phase transition for the doped samples. Also, the maximum dielectric constant value (ε′_max) decreased while the phase transition temperature increased with increase in doping concentration of Ni. The estimated activation energy of different compositions was found to increase from 0.057 to 0.068?eV for x?=?0.00 to x?=?0.20 in ferroelectric phase. The piezoelectric, ferroelectric and magnetic properties were also investigated.     

The PZT system (PbTixZr1–xO3, 0≤x≤1.0): The real phase diagram of solid solutions (room temperature) (Part 2)

The sequence of phase transformations in the ceramic system PbTi_xZr_1?xO₃ (0≤x≤1.0) is determined and the real phase diagram of solid solutions is built. The observed periodicity of phase formation processes in the rhombohedral and tetragonal regions is explained by the real (defective) structure of PZT system ceramics, which is in many respects related to the variable valence of Ti ions and, as a result, to formation, accumulation, and ordering of point defects (oxygen vacancies) and their elimination by crystallographic shifts. The obtained results are useful in interpretation of the macroscopic properties of ceramics based on the PZT system.     

Effect of ZnO nano-particulate modification on properties of PZT–BLT ceramics

This research was conducted to study the effect of ZnO nano-particulate modification on properties of Pb(Zr_0.52Ti_0.48)O₃ (PZT)–(Bi_3.25La_0.75)Ti₃O₁₂ (BLT) ceramics prepared by a mixed-oxide solid-state sintering method. ZnO nano-particulate was added into PZT–BLT ceramics to obtain PZT–BLT/xZnO (x = 0, 0.1, 0.5 and 1.0 wt%). The PZT–BLT/xZnO ceramics were investigated in terms of phase, microstructure, physical, electrical, and mechanical properties. Tetragonality of PZT–BLT crystal structure tended to increase with increasing ZnO content. ZnO addition obviously increased the density of PZT–BLT ceramics while the grain size slightly decreased. Intergranular fracture mode was observed for pure PZT–BLT ceramic while the samples contained ZnO nano-particles showed a mixed-mode inter-/trans-granular fracture. Addition of ZnO also affected hardness and fracture toughness values. Addition of ZnO nano-particulate into PZT–BLT ceramics was found to improve room temperature dielectric constant but did not have a significant effect on ferroelectric properties. These observed results were expected to be caused by the behaviors similar to a donor-doped system.     

Ferroelastic Properties of Lead Zirconate Titanate Ceramics

To increase the reliability of multilayer actuators, calculation of the mechanical stress inside the device during operation is important. This paper shows that the small-signal value of the elastic constant s is not sufficient to describe the complicated behavior of lead zirconate titanate (PZT) ceramics. Therefore, compressive strain and depolarization have been measured as a function of large-signal stress applied parallel to the poling direction. The nonlinear dependence of the strain and depolarization can clearly be explained by domain processes. Soft and hard PZT ceramics have been investigated. In hard PZT, domain switching appears at higher stresses than in soft PZT. Moreover, in hard PZT, the domains partly switch back during unloading. The critical stress (coercive stress) necessary for a domain-switching process shows a dependence on the Zr:Ti ratio that is quite similar to the dependence of the electric coercive field. The influence of an electric field applied parallel to the poling direction and superimposed on the compression experiment also has been examined. The coercive stress depends linearly on the electric field. The linear coefficient of this relation is given by the ratio of depolarization to compressive strain caused by domain switching.     

Domain Switching During Electromechanical Poling in Lead Zirconate Titanate Ceramics

In many polycrystalline piezoelectric ceramics, domain switching during the poling process leads to the development of a macroscopic polarization and piezoelectric behavior. Traditionally, poling involves the application of electric fields across two parallel electrodes. In the present work, a radial mechanical compressive stress is applied transverse to the electric field, increasing the potential for domain alignment during poling by taking advantage of ferroelasticity. Experiments demonstrate that poling of lead zirconate titanate using a combination of an electric field and a transverse mechanical compressive stress increases the d ₃₃ coefficient from 435 to 489 pC/N. Using neutron diffraction and pole figure inversion methods, the degree of non-180° domain switching is described using pole density distributions of the tetragonal c -axis (002). The degree of 002 domain alignment parallel to the electric field after the electromechanical poling process increases from 1.30 multiples of a random distribution (mrd) to >1.40 mrd at stresses exceeding 40 MPa.     

Fatigue failure characteristics of lead zirconate titanate piezoelectric ceramics

Mechanical properties and fatigue failure characteristics of lead zirconate titanate piezoelectric ceramic (PZT) have been investigated. Bending and fatigue strengths of PZT ceramic are directly attributed to the electrode status. Material hardening occurs in the PZT ceramic during the cyclic loading, which is influenced by domain switching occurring anywhere in the grains. The domain structure is clearly detected by electron back scatter diffraction analysis and etching techniques. It also appears that the poling direction causes the change of failure characteristics due to different domain and domain wall orientation. The domain orientation changes alternately from domain to domain by 90°. Moreover, the domain wall orientation is well regulated in the grains perpendicular to the poling direction. An acceleration of fatigue crack growth occurs as the crack propagates along the domain wall.     

Study of phase transition line of PZT ceramics by X-ray diffraction

The transition line between tetragonal and rhombohedral phases in PZT ceramics has been studied on the basis of X-ray diffraction data, with a view to establishing the morphotropic phase boundary (MPB). In ceramic manufacturing technology, piezoelectric PZT ceramic compositions are most likely to be near the morphotropic phase boundary. This boundary can move when even small levels of dopants are present in the PZT ceramics.     

Phase formation,electrical properties and morphotropic phase boundary of 0.95Pb(ZrxTi1−x)O3–0.05Pb(Mn1/3Nb2/3)O3 ceramics

Ferroelectric ceramics in specific composition of 0.95Pb(Zr_xTi_1?x)O₃–0.05Pb(Mn_1/3Nb_2/3)O₃ or PZT–PMnN (with x=0.46, 0.48, 0.50, 0.52, and 0.54) have been investigated in order to identify the morphotropic phase boundary (MPB) composition. The effects of Zr/Ti ratio on phase formation, dielectric and ferroelectric properties of the specimens have also been investigated and discussed. X-ray diffraction patterns indicate that the MPB of the tetragonal and rhombohedral phase lies in x=0.52. The crystal structure of PZT–PMnN appeared to change gradually from tetragonal to rhombohedral phase with increasing Zr content. The dielectric and ferroelectric properties measurements also show a maximum value (ε_r, tan δ and P_r) at Zr/Ti=52/48, while the transition temperature decreases with increasing Zr content.