Dielectric Properties and Microstructures of Ba(Ti,Zr)O3 Multilayer Ceramic Capacitors with Ni Electrodes

The microstructures and dielectric properties of multilayer ceramic capacitors based on reoxidized Ba(Ti_0.88,Zr_0.12)O₃ (BTZ) materials with Ni electrodes were studied using transmission electron microscopy. Dielectric measurements showed that the BTZ materials exhibited frequency relaxation effects. Although X-ray diffraction showed a single pseudocubic phase, split and elongated electron diffraction spots were observed using selected area diffraction (SAD). There were no super-lattice diffraction spots in the SAD pattern. The microstructures of BTZ dielectric materials were observed at dynamical diffraction conditions, and multidomain structures coexisting in one grain were imaged with high contrast. Bright field and centered dark field images revealed the pseudocubic (100) and (110) domain walls had developed in some regions of the same grain with normal ferroelectric macro-domain features, and bend contours and distorted domain walls were seen. Defects with the features of low angle grain boundaries, dislocations, and phase boundaries were also observed. Uneven distribution of internal stress and coexistence of multiphases and multidomains in individual grains were considered to be responsible for the frequency relaxor behavior observed in these materials. A model of the evolution of the microstructures with the decrease of temperature is presented.     

Dielectric Properties of Ba(Zr,Ti)O3-Based Ferroelectrics for Capacitor Applications

The purpose of the present investigation is to describe the influence of the processing parameters on the dielectric behavior of manganese-doped Ba(Ti_{1− x} Zr _x )O₃ceramics, particularly variations in the small-signal aging rate, temperature characteristic, and hysteresis. In this paper, the aging behavior of base-metal electrode materials above the temperature of the permittivity maximum ( T _M), including the influence of the zirconium content and annealing conditions, is described for the first time. The aging rate at temperatures greater than T _M decreases as the oxygen partial pressure increases during annealing and the zirconium content increases, whereas the aging rate exhibits a maximum at temperatures much less than T _M. The behavior is explained in terms of a diffuse phase transition. Hysteresis-loop deformation is observed during aging.     

The Ba(Ti,Zr)O3–(Zr,Ti)O2 Field in the Phase System BaO–TiO2–ZrO2

The two-phase field involves a ZrO₂-TiO₂ solid solution containing no more than 4 mol% TiO₂, and a BaTiO₃-BaZrO₃ solid solution containing a maximum of 75 mol% BaTiO₃. The field narrows above 1300°C, probably because of the intrusion of a liquid-phase field into the ternary, beginning near the BaO-TiO₂ edge.     

Dielectric and Structural Studies in the Systems Ba(Ti, Nb)O3 and Ba(Ti, Ta)O3

The dielectric properties, lattice parameters, and X-ray and neutron diffraction intensities of solid solutions of BaTiO₃ containing Nb or Ta were studied. These solid solutions have a perovskite-type structure with part of the Ti⁴⁺ ions replaced by Nb⁵⁺ or Ta⁶⁺ ions and with some cation vacancies. These solid solutions exhibit a remarkable lowering of the Curie point, but the tetragonal-orthorhombic and the orthorhombic-rhombohedral transition points are raised.     

Structural and Dielectric Studies in the System (Ba, Ca) (Ti, Zr)O3

The crystalline phases in the system (Ba, Ca) (Ti, Zr)O₃ were identified and their lattice dimensions were determined from X-ray powder patterns of fired ceramic disks. Compositions near the BaTiO₃-BaZrO₃ and CaTiO₃-CaZrO₃ sides of the composition square gave evidence of complete solid solution, whereas all intermediate compositions contained two separate phases. Variations in the temperature of the Curie point and in aging rate were found to correlate reasonably well with variations in the character of the crystal structure.     

Low-Field Depoling Characteristics of Pb(Zr, Ti)O3 Ceramics

Low-electric-field depoling measurements were made on Pb(Zr, Ti)O₃ ceramics. The apparent activation energy for the depoling process was calculated to be 33 kcal/mol. The data indicate that the materials tested should be very stable when subjected to depoling fields on the order of one-fourth of the coercive field.     

Effects of Calcination Temperature and A/B Ratio on the Dielectric Properties of (Ba,Ca)(Ti,Zr,Mn)O3 for Multilayer Ceramic Capacitors with Nickel Electrodes

The electrical performance of multilayer ceramic capacitors (MLCCs) with Ni inner electrodes, made from (Ba,Ca)(Ti,Zr,Mn)O₃ (BCTZM), is closely related to the calcination temperature and the A/B ratio of the powder. For materials showing A/B = 1.000, the lifetime, the breakdown voltage, and the RC increase with higher calcination temperatures. No significant effect of the calcination temperature on RC and lifetime was found for materials showing A/B = 0.991. The isoelectric point of BCTZM is shifted toward higher pH values when the calcination temperature is decreased. The above results are attributed to the colloidal stability of aqueous BCTZM suspensions and the resulting green density of powder compacts.     

Structure and Dielectric Properties of Pb(Sc2/3W1/3)O3–Pb(Zr/Ti)O3 Relaxors

The structure and dielectric properties of (1− x )Pb(Sc_2/3W_1/3)O₃–( x )Pb(Zr/Ti)O₃ ceramics have been investigated over a full substitution range. All compositions with x < 0.5 adopt a cubic perovskite structure; however, for x ≤ 0.25 a doubled cell results from a 1:1 ordered distribution of the B-site cations. The structural order in Pb(Sc_2/3W_1/3)O₃ (PSW) can be described by a random-site model with one cation site occupied by Sc³⁺ and the other by a random distribution of (Sc_1/3³⁺W_2/3⁶⁺). The ordering is destabilized in solid solutions of PSW with PbZrO₃ (PSW–PZ), but stabilized by PbTiO₃ in the (1− x )PSW–( x )PT system. The changes in order are accompanied by alterations in the dielectric response of the two systems. For PSW–PZ the temperature of the permittivity maximum ( T _ɛ,max) increases linearly with x ; however, for PSW–PT T _ɛ,max decreases in the ordered region (up to x = 0.25) and then increases rapidly as the order is lost. Similar effects were produced by modifying the degree of order of (0.75)PSW–(0.25)PT; when the order parameter was reduced from ∼1.0 to ∼0.65, T _ɛ,max increased by more than 60°C.     

Optical Study of Domains in Ba(Ti,Sn)O3 Ceramics

Domain structures of Ba(Ti_1−xSn_x)O₃ (x = 0, 0.05, 0.1, 0.13) ceramics were observed dynamically under an electric field at various temperatures using a high-resolution charge-coupled-device (CCD) microscope system. The Ba(Ti_1−xSn_x)O₃ ceramics showed a significant difference in domain structure and motion with changing composition: the domain structure became tiny and complex with increasing x , and the domain reorientation was easily induced with increasing and decreasing electric field. The results of the domain observations coincided well with electrical measurement data.     

Effect of Simultaneous Addition of BiFeO3 and Ba(Cu0.5W0.5)O3 on Lowering of Sintering Temperature of Pb(Zr,Ti)O3 Ceramics

Sintering of 0.5-wt%-MnO₂-added Pb(Zr_0.53Ti_0.47)O₃ ceramics progresses at 935°C for 50 min by the addition of complex oxides of perovskite-type crystal structure, BiFeO₃ and Ba(Cu_0.5W_0.5)O₃. In order to elucidate the low-temperature sintering mechanism of Pb(Zr,Ti)O₃ ceramics, the shrinkage and the evolution of the microstructure of a compacted body during heating were studied. It has been shown that the densification process was separated into the following three stages: the rearrangement of grains, the grain boundary diffusion of atoms, and then grain growth. Also, microstructural and elemental analyses of the ceramics revealed the existence of an amorphous phase at the grain boundaries predominantly composed of lead and copper oxides. Consequently, this process can be facilitated by the occurrence of a transient liquid phase corresponding to the above amorphous phase.     

Highly Oriented, Chemically Prepared Pb(Zr, Ti)O3 Thin Films

We have fabricated highly oriented, chemically prepared thin films of Pb(Zr_0.04Tio._0.60)O₃ (PZT 40/60) on both insulating and conducting substrates. While (100) MgO single crystals were used as the insulating substrates, the conducting substrates. were fabricated by RF magnetron sputter deposition of 100-nm-thick (100) Pt films onto (100) MgO substrates. For comparison, we also fabricated PZT 40/60 films that had no significant preferential orientation on platinized MgO substrates. Sputter deposition of an underlying amorphous Pt film was used to fabricate randomly oriented PZT 40/60 films. Highly (001) oriented PZT 40/60 films had higher remanent polarization (61 μC/cm² compared to 41 μC/cm²) and lower relative dielectric constant (368 compared to 466) than PZT 40/60 films that were randomly oriented.     

Effect of Additives on the Electromechanical Properties of Pb(Zr,Ti)O3–Pb(Y2/3W1/3)O3 Ceramics

Dielectric and piezoelectric properties of 0.02Pb(Y_2/3W_1/3)O₃ 0.98Pb(Zr0.52Ti0.48)O3 ceramics doped with additives (Nb₂O₅, La₂O₃, MnO₂, and Fe₂O₃) were investigated. The grain sizes of these ceramics decreased with increasing amounts of additives. For additions of MnO₂ and Fe₂O₃, dielectric losses decreased, while for Nb₂O₅ and La₂O₃, these values increased. The maximum values of the mechanical quality factor Q_m were found to be 956 and 975 for additions of 0.9 wt% Fe₂O₃ and 0.7 wt% MnO₂, respectively, but donor dopants (Nb₂O₅ and La₂O₃) did not change the values of Q_m . On the other hand, the piezoelectric constant d₃₃ and the electromechanical coupling factor k_p decreased with additions of MnO₂ and Fe₂O₃, but improved with additions of Nb₂O₅ and La₂O₃.     

Preparation of Full-Dense Pb(Zr,Ti)O3 Ceramics by Aerosol Deposition

Full-dense fine-grained bulk Pb(Zr,Ti)O₃ (PZT) ceramics with a thicknesses of 300 μm were successfully obtained by aerosol deposition (AD) employing the starting powder subjected to an adequate pretreatment. It was found that formation of internal pores during the postdeposition firing treatment takes place in two different mechanisms on different scales. Residual carbons contained in the as-deposited PZT ceramics are responsible for the formation of extra-large pores, inducing severe distortion to the shape of the sample. On the other hand, trapped agglomerates in the as-deposited PZT ceramics are responsible for the formation of intermediate pores. The revealed mechanisms are discussed with a focus on the positive/negative correlation between the pretreatment procedure of starting powders and the formation of internal pores.     

Shape Evolution of Pb (Zr,Ti)O3 Nanocrystals Under Hydrothermal Conditions

Pb (Zr,Ti)O₃ nanocrystals with different morphologies have been prepared hydrothermally with poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) as surfactants. The morphology of Pb (Zr,Ti)O₃ nanocrystals develops from a particle to a rod and then a wire by adjusting the ratio of PVA/PAA and reaction time in a hydrothermal system. The mixed surfactant system has been shown to promote anisotropic growth effectively and thus the formation of nanorods and single crystalline nanowires of Pb (Zr,Ti)O₃. A possible mechanism for such a shape evolution of nanocrystals is simply discussed.     

Low Temperature Coefficient of Resonance Frequency Composition in the System Pb(Zr,Ti)O3—Pb(Mn1/3 Nb2/3)O3

Pb(Zr,Ti)O₃–Pb(Mn_1/3 Nb_2/3)O₃ (PZT–PMnN) system has been studied for high-power piezoelectric applications. This study investigates this system to find out the composition with high-power density piezoelectric characteristics and low tem-perature coefficient of resonance frequency (TCF). It was found that the composition 0.9PZT–0.1PMnN (Zr/Ti = 0.51/0.49) modified with 6 mol% Sr exhibits a TCF of −8 ppm/°C (−20 to +80°C). Further, the dielectric and piezoelectric properties of this composition are as follows: k _p= 0.53; Q _m= 800; d ₃₃= 274; ε₃₃/ε₀= 1290 and tan δ=1.1%, which shows the suitability of this composition for ultrasonic devices used under fluctuating thermal environment.     

Excimer Laser Crystallized (Pb,La)(Zr,Ti)O3 Thin Films

A KrF pulsed excimer laser (248 nm) was utilized to crystallize sputtered La-modified Pb(Zr,Ti)O₃ (3:30:70) (PLZT) films on LaNiO₃-coated silicon substrates. The film surface was irradiated with defocused laser pulses in an oxygen ambient at various substrate temperatures. Polycrystalline, phase pure perovskite PLZT thin films were produced for substrate temperatures of 250°C and higher. The dielectric constant and loss tangent values of laser-assisted crystallized (10 min exposure at 10 Hz using a substrate temperature of 400°C) PLZT thin films at 10 kHz were 406 and 0.027; in comparison, rapid thermal annealed films (annealed at 700°C for 1 min) showed values of 400 and 0.021, respectively. Laser crystallized films exhibited a remanent polarization value of 14 μC/cm² with a coercive field |( E _+c+ E _−c)|/2 of 95 kV/cm.     

Influence of [Ba + Ca]/[Ti + Zr] Ratio on the Interfacial Property of (Ba,Ca)(Ti,Zr)O3 (BCTZ) Powders in an Aqueous Medium

We report findings on the electrokinetic and solubility behaviors of (Ba,Ca)(Ti,Zr)O₃ (BCTZ) powders having three different [Ba + Ca]/[Ti + Zr] ratios: 0.995, 1.000, and 1.005. Electrokinetic and solubility properties of BCTZ powders in aqueous media are phenomenologically similar to BaTiO₃. Ba and Ca ions, occupying primarily A-sites on the perovskite lattice, dissolve during acid titration, which results in surface depletion of A-site cations in the surface region of BCTZ particles. The electrokinetics of colloidal BCTZ powders reflects changes in the surface chemistry that occur as a result of dissolution and adsorption/reprecipitation of surface ions. An increase in [Ba + Ca]/[Ti + Zr] ratio results in an increase in the dynamic mobility at all pH values, an increase in the titration hysteresis, and an increase in the isoelectric pH. Each of these effects can be attributed to Ba and Ca in the near-surface region of BCTZ.     

Microstructure and Electrical Properties of (K, Na, Li)NbO3–Pb(Zr,Ti)O3 Piezoelectric Ceramics

A new type (1− x )(K_0.485Na_0.485Li_0.03)NbO₃– x Pb(Zr_0.53Ti_0.47)O₃ piezoelectric ceramics was fabricated by conventional ceramics sintering technique. Their microstructure and electrical properties of the ceramics were also studied. X-ray diffraction and scanning electron microscopy patterns indicate that all ceramics samples exhibit a pure perovskite and highly dense structure, and the coexistence of the tetragonal and orthorhombic phases is formed; The ceramic with x =0.75 exhibits the following excellent properties: d ₃₃=363 pC/N, k _p=63%, Q _m=142, ɛ_r=1590, tan δ=1.70%, P _r=28.6 μC/cm², E _c=0.89 kV/mm, T _c=295°C. These results indicate that the ceramic is a promising candidate for piezoelectric ceramics in practical applications.