Effect of Cr additions on the electrical properties of Ni–BaTiO3 ultra-thin multilayer capacitors

Multilayer ceramic capacitors based on BaTiO₃ dielectric compositions and Ni inner electrodes have complex interfacial reactions that impact the continuity of the inner electrode microstructure. Previously we demonstrated that through the addition of Cr to Ni, a significant improvement in the continuity of ultra-thin Ni electrodes in Ni–BaTiO₃ multilayer capacitors could be achieved. Here, the effect of the Cr addition to the nickel electrode pastes is studied with regard to the electrical properties. Low-field electrical measurements demonstrate no major differences between Cr doped Ni and undoped Ni. However, high-field measurements show a significant decrease to the total capacitor resistance. Under a critical electrical bias the conductivity significantly increases due to a Fowler–Nordheim tunneling conduction though the interfacial Schottky barrier at the dielectric–electrode interface; the onset voltage of this conduction is much lower than with the undoped nickel. Based on these results, we evaluate criteria for the selection of an appropriate refractory metal in order to improve the Ni electrode continuity.     

Microstructure analysis of the Y5V multilayer ceramic capacitors based on BaTiO3

The Y5V-1206 base-metal electrode (BME) multilayer ceramic capacitor (MLCC) chips have been characterised for crystalline phases using X-ray diffractometry (XRD), and microstructure using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microstructure features found in the Ni electrode and the BaTiO₃ dielectric layer are discussed in terms of the tensile backstresses induced upon firing due to constrained sintering heterogeneously. The chemical compositions containing BaO-excess and additives CaO and ZrO₂, determined for BaTiO₃ grains by energy-dispersive spectroscopy (EDS) equipped in the TEM are also reported. However, no rare-earth oxides were found in the grains. The representative microstructure of BaTiO₃ grains containing dislocations is the “solid-solution” type distinctive from the “core-shell” of the X7R compositions. The fact that no ferroelectric domains were detected suggests that the BaTiO₃ grains are pseudo-cubic with the c/a ratio ≈ 1.0.     

Lead-free (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)<Subscript>0.95</Subscript>(LiSb)<Subscript>0.05</Subscript>Nb<Subscript>0.95</Subscript>O<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> piezoceramics

Lead-free (1-x)(K_0.5Na_0.5)_0.95(LiSb)_0.05Nb_0.95O₃-xBaTiO₃ (abbreviated as (1-x)KNNLS-xBT) piezoceramics were synthesized by conventional solid state sintering and the effect of BaTiO₃ on the microstructure, dielectric and piezoelectric properties was investigated. It was found that both orthorhombic-tetragonal (T _O-T) and tetragonal-cubic (T _C) phase transition temperatures decreased obviously with increasing BaTiO₃ content. Although proper amount of BaTiO₃ facilitated the sintering of (1-x)KNNLS-xBT ceramics, the addition of BaTiO₃ affected the relaxor behavior slightly and it was not beneficial to improve piezoelectric strain coefficient d ₃₃, remnant polarization P _r and piezoelectric coupling constant k _p.     

Raman and infrared spectroscopy of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> - BaTiO<Subscript>3</Subscript> ceramics

Lead-free Na_0.5Bi_0.5TiO₃ -BaTiO₃ ceramics have been prepared in the whole range of concentrations and studied at room-temperature by means of X-ray, Raman scattering and infrared techniques. X-ray measurements revealed rhombohedral, rhombohedral-tetragonal boundaries and tetragonal modifacations depending on the contents of BaTiO₃. The distinct changes of the Raman and infrared spectra with increasing of BaTiO₃ content, which were correlated with X-ray results, were observed. The broad phonon spectra indicated the disorder in the A site of Na_0.5Bi_0.5TiO₃ -BaTiO₃ system.     

Preparation and modification of high Curie point BaTiO<Subscript>3</Subscript>-based X9R ceramics

BaTiO₃ (BT) based X9R ceramics with high permittivity about 1700 were prepared by doping and pre-sintering technique. Pure Bi_0.5Na_0.5TiO₃ (BNT) dopant was synthesized by the conventional solid state reaction first. Using this new approach, high performance BTBNT (BT doped with BNT) materials, owning high Curie temperature (139 °C), flat ferroelectric transition region and large permittivity at room temperature, were obtained. The effects of several dopants on dielectric properties of BTBNT ceramics were measured by the LCR meter. The suppression effect for the peaks in the dielectric constant at Curie temperature of these dopants have been ranked as follows: BiNbO₄ > CaZrO₃ > Nb₂O₅ > BNT.     

Effect of SiO<Subscript>2</Subscript> Addition to BaO-ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> Glass on Dielectric and Thermal Properties for Application to Barrier Ribs of Plasma Display Panels

The effect of SiO₂ addition to barium zinc borate (BaO-ZnO-B₂O₃, BZB) glass on dielectric and thermal expansion properties was investigated. When SiO₂ was added to the glass batch to form a SiO₂-BaO-ZnO-B₂O₃ (SBZB) glass, the dielectric constant decreased significantly from 15.5 to 9.9. When SiO₂ (quartz) was further added to the SBZB in the form of filler particles to yield ceramic filler-reinforced SBZB microcomposites, the dielectric constant was further decreased. The coefficient of thermal expansion (CTE) of SBZB was slightly lower than the allowable range, while the filler addition to SBZB correspondingly increased CTE to the allowable range. Thus, the addition of SiO₂ to BZB glass to form SBZB glass and further addition to SBZB in the form of ceramic filler were shown to be amenable ways to tailor the dielectric constant as well as CTE of the barrier rib glass for the PDP application.     

Effects of Oxide Additives Coating on Microstructure and Dielectric Properties of BaTiO3

Effects of mixing methods (mechanical mixing, chemical coating) on microstructure and dielectric properties of Ho, Mg and Mn doped BaTiO₃ have been studied. BaTiO₃ particles coated with Ho, Mn and Mg were prepared by a homogeneous precipitation method using urea, and then silica was coated by the sol-gel technique. The adsorption of additives on the BaTiO₃ surface was confirmed. Temperature characteristics of capacitance were satisfied by mechanical mixing and chemical coating techniques, both of which yield different sintering and microstructure behaviors. Pyrochlore phase (Ho₂Ti₂O₇) was observed on the mechanically mixed sample, whereas none of pyrochlore phase was observed at the coated sample after thermal etching. Those different behaviors caused by the degree of homogeneous distribution of the additives in BaTiO₃ matrix were confirmed by EDS analysis.     

Characterization of Barium Titanate: BaTiO<Subscript>3</Subscript> (BT) Ceramics Prepared from Sol-Gel Derived BT Powders

Sol-gel synthesis was attempted at room temperature by adding drop wise a clear solution (made by reacting BaCO₃ with glacial acetic acid) to an equi-molar solution of titanium tetrabutoxide in isopropanol (IPA) and acetic acid. The gelation occurred within 30 minutes. The as-dried gel was calcined at 750^∘C/6 h in air to obtain carbon free BaTiO₃ powders. The resulting BT powders were further pressed into pellets and sintered at 1280^∘C/4 h in air to get dense ceramics (density ∼ 94%). XRD and SEM techniques were used for phase and microstructure analysis respectively. The room temperature relative permittivity (ε) of 1280 increased to 7200 (at Curie temperature of 127^∘C) at 1 kHz frequency. The dissipation factor (tanδ) ∼1.6% was observed in these samples. Also, the ferroelectric properties such as spontaneous polarization (Ps ∼ 13 μC/cm²), coercive field (E_c∼4.0 kV/cm) and dielectric strength (∼34 kV/cm) are estimated for these samples. These performance parameters are compared with the available standard data from the literature.     

Microwave Dielectric Properties of CuO-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Doped ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript> Ceramics with Low Sintering Temperature

Microwave dielectric properties of low temperature sintering ZnNb₂O₆ ceramics doped with CuO-V₂O₅-Bi₂O₃ additions were investigated systematically. The co-doping of CuO, V₂O₅ and Bi₂O₃ can significantly lower the sintering temperature of ZnNb₂O₆ ceramics from 1150 to 870C. The secondary phase containing Cu, V, Bi and Zn was observed at grain boundary junctions, and the amount of secondary phase increased with increasing CuO-V₂O₅-Bi₂O₃ content. The dielectric properties at microwave frequencies (7–9 GHz) in this system exhibited a significant dependence on the relative density, content of additives and microstructure of the ceramics. The dielectric constant ( _r) of ZnNb₂O₆ ceramics increased from 21.95 to 24.18 with increasing CuO-V₂O₅-Bi₂O₃ additions from 1.5 to 4.0 wt%. The quality factors (Q× f) of this system decreased with increasing CuO-V₂O₅-Bi₂O₃ content and ranged from 36118 to 67100 GHz for sintered ceramics, furthermore, all Q× f values of samples with CuO-V₂O₅-Bi₂O₃ additions are lower than that of un-doped ZnNb₂O₆ ceramics sintered at 1150C for 2 h. The temperature coefficient of resonant frequency ( _f) changed from –33.16 to –25.96 ppm/C with increasing CuO-V₂O₅-Bi₂O₃ from 1.5 to 4.0 wt%     

Effect of Cr additions on the microstructural stability of Ni electrodes in ultra-thin BaTiO3 multilayer capacitors

Microstructural control in thin-layer multilayer ceramic capacitors (MLCC) is one of the present day challenges to maintain an increase in capacitive volumetric efficiency. This present paper opens a series of investigations aimed to engineer the stability of ultra-thin Ni electrodes in BaTiO₃-based multilayer capacitors using refractory metal additions to Ni. Here, pure Ni and Ni–1 wt.% Cr alloy powders are used to produce 0805-type BME MLCCs with 300 active layers and with dielectric and electrode layer thickness around 1 μm. To investigate the continuity of Ni electrodes, both MLCC chips with pure and doped electrodes were sintered at different temperatures for 5 h. It is found that the continuity of Ni electrodes is improved most likely due to the effect of Cr on the low-melting point (Ni,Ba,Ti) interfacial alloy layer formation. The interfacial alloy layer is not observed when Cr is segregated at Ni-BaTiO₃ interface in the Cr-doped samples, while it is found in all undoped samples. The interfacial alloy layer is believed to increase mass-transfer along the Ni-BaTiO₃ interfaces facilitating an acceleration of Ni electrodes discontinuities.     

Moldless micropatterning of BaTiO<Subscript>3</Subscript> nanoparticles via electrophoretic deposition: A simple and feasible method

In this work, a simple, reproducible, and inexpensive fabrication route for moldless micropatterning of a colloidal assembly on a conducting substrate surface is actualized by means of electrophoretic deposition (EPD) technique. A synergetic combination of photolithography and EPD is employed for fabricating micropatterns of barium titanate (BaTiO₃) nanoparticles on an indium-tin-oxide (ITO) coated glass slide or a Pt/ITO substrate. At first, high quality resist molds with various micropatterns are fabricated on ITO glass slide by photolithography technique, which is used for providing a controlled local electric field during the EPD process. Then, BaTiO₃ nanoparticles suspension is prepared in KCl aqueous solution and is demonstrated the BaTiO₃ nanoparticles are negative charged in the suspension. At last, EPD of various BaTiO₃ micropatterns is accomplished successfully on the anodic ITO glass slide or Pt/ITO substrate using the micropatterned ITO glass slide as the cathode, indicating that it is a simple and potential route for micropatterning of colloidal assembly on a non-modified conducting substrate by virtue of EPD process.     

An insight into thermal and vibration cyclic energy harvesting using ferroelectric ceramics

This article reviews the basics of ferroelectric energy harvesting cycles based on thermal fluctuation and mechanical confinement. In this context, five cycles (Olsen cycle, Clamped Olsen cycle, Electro-Mechanical cycle, Thermally Biased Electro-Mechanical cycle and New Power cycle) are studied for two different compositions (0.94Bi_1/2Na_1/2TiO₃–0.06BaTiO₃: BNT–6BT; 0.91(Bi_1/2Na_1/2)TiO₃–0.07BaTiO₃–0.02K_0.5Na_0.5NbO₃: BNT-BT-KNN;) which represents two distinct classes (based on domain wall rotation/motion) of ferroelectric materials. These can be classified as the composition with dominating impact of mechanical forces while the other is with ascendant thermal effects over the domain wall behavior.     

Dielectric Properties and Sintering Characteristics of CaTiO<Subscript>3</Subscript>-(Li<Subscript>1/2</Subscript>Nd<Subscript>1/2</Subscript>)TiO<Subscript>3</Subscript> Ceramics

The dielectric properties and the sintering effect upon microstructure of (1–x) CaTiO₃-x(Li_1/2Nd_1/2)-TiO₃ Ceramics are investigated in this paper. Nd³⁺ and Mg^{2 +} ions co-substitution for Ca^{2 +} on A site improves the sintering characteristic of CaTiO₃ ceramics with forming orthorhombic perovskite structure. The structure of (1 – x) CaTiO₃-x(Li_1/2Nd_1/2)TiO₃ changes from orthorhombic to tetragonal as (Li_1/2Nd_1/2)TiO₃ addition increasing. Limited solubility of (Li_1/2Nd_1/2)TiO₃ in CaTiO₃ forming a part solid solution compound achieves the adjustment of for CaTiO₃ at low sintering temperature. The proper dielectric properties with = 78, tan = 0.0006, = +7 ppm/C are obtained for 0.8Ca_0.67(Nd,Mg)_0.22TiO₃-0.2(Li_1/2Nd_1/2)TiO₃ ceramics.     

Effects of MnO<Subscript>2</Subscript> addition on microstructure and electrical properties of (Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>) <Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> ceramics

In this letter, MnO₂-doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNBT-6) lead-free piezoelectric ceramics were synthesized by solid state reaction, and the microstructure and electrical properties of the ceramics were investigated. X-ray diffraction (XRD) reveals that all specimens take on single perovskite type structure, and the diffraction peaks shift to a large angle as the MnO₂ addition increases. Scanning electron microscopy shows that the grain sizes increases, and then decreases with increasing the MnO₂ content. The experiment results indicate that the electrical properties of ceramics are significantly influenced by the MnO₂ content, and the ceramics with homogeneous microstructure and excellent electrical properties are obtained with addition of 0.3 wt% MnO₂ and sintered at 1160°C. The piezoelectric constant (d₃₃), the electromechanical coupling factor (k _p ), the dissipation factor (tan δ) and the dielectric constant (ɛ _r ) reach 160 pC/N, 0.29, 0.026 and 879, respectively. These excellent properties indicate that the MnO₂-doped BNBT-6 ceramics can be used for actuators.     

Dielectric and Piezoelectric Properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-K<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-NaNbO<Subscript>3</Subscript>Lead-Free Ceramics

The ternary lead-free piezoelectric ceramics system of (1 – x) [0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃] – xNaNbO₃(x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) were synthesized by conventional solid state reaction method. The crystal structure, dielectric, piezoelectric properties and P-E hysteresis loops were investigated. The crystalline structure of all compositions is mono-perovskite phase ascertained by XRD, and the lattice constant was calculated from the XRD data. Temperature dependence of dielectric constant _r and dissipation factor tan measurement revealed that all compositions experienced two phase transitions: from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric, and these two phase transitions have relaxor characteristics. Both transition temperatures T_d and T_m are lowered due to introduction of NaNbO₃. P-E hysteresis loops show that 0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃ ceramics has the maximum P_r and E_c corresponding to the maximum values of electromechanical coupling factor K_p and piezoelectric constant d_33. The piezoelectric constant d₃₃ and electromechanical coupling factor K_p decrease a little, while the dielectric constant ₃₃^T/₀ improves much more when the concentration of NaNbO₃ is 8 mol%.     

The effect of transition-metal addition on the non-equilibrium E.M.F.-type gas sensor

In this study, we made single chamber gas sensor which had two SnO₂ electrodes pasted onto either side of zirconia electrolyte. Transition metal (TM) was added in one of two SnO₂ electrodes to induce and thus confirm the catalytic effect of transition-metal. Since 1 mol% TM-doped SnO₂ showed the negligible change in microstructure, the effect of microstructure change could be ignored. The Co addition increased the e.m.f. of working electrode (TM-added SnO₂) in air, implying the enhanced oxygen adsorption. The addition of TM to SnO₂ was also effective in changing the e.m.f. values in H₂ balanced by air. Fe and Ni addition exhibited decreased e.m.f. in H₂ from that in air. Thus, Fe and Ni addition improved the catalytic activity for H₂ oxidation. Cu addition slightly improved the catalytic activity for CO oxidation. The results show that Co is expected to be a good additive for the cathode of solid-oxide-fuel-cell (SOFC) at low temperature. On the other hand, Fe, Cu, or Ni is good additives for anode.     

Sol-gel PZT thin films on nickel alloy electrodes

Abstract

The Ni alloy electrode was used for a bottom electrode of PZT thin films prepared by sol-gel process. Although PZT films were crystallized on soda–lime glass substrates with the alloy electrodes at a relatively low temperature of 500°C, second phases of Pb₃O₄ and ZrTiO₄ were produced on the electrode in addition to the perovskite PZT phase. In order to prevent the second phases forming, the heat treatment time of the electrode was increased to obtain the thicker Al₂O₃ layer on the alloy electrode. The second phases decreased with increasing the heat treatment time; however, the phases did not disappear. When BaTiO₃ films were inserted between the electrodes and PZT films, the PZT single phase was obtained. The tan δ of the films decreased with decreasing the amount of the second phases, finally it became 3.9%, the film of which possessed a remanent polarization of 20 μC/cm².     

Site Preference of La in Bi<Subscript>3.75</Subscript>La<Subscript>0.25</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Using Neutron Powder Diffraction and Raman Scattering

Both structural refinement using neutron powder diffraction data and Raman scattering were carried out to determine the site preference of La atoms and the cation distribution in Bi_3.75La_0.25Ti₃O₁₂ compound. Of three possible cation-disorder models, the best structural refinement result was obtained from a model that La atoms substitute only for Bi atoms outside of the TiO₆ octahedra in the Bi₂Ti₃O₁₀ unit. The model proposed by the structural refinement was corroborated by the Raman spectroscopic study. The final weighted R-factor, R_wp, and the goodness-of-fit indicator, S (= R_wp/R_e), based on the neutron diffraction and the Raman scattering were 4.12% and 1.43, respectively. The occupancy of La atoms for two Bi sites in the perovskite-like unit was 0.082 and 0.074, respectively. The refined model described a structure in monoclinic space group B1a1 with Z = 4, a = 5.4387(1) Å, b = 5.4129(1) Å, c = 32.8441(1) Å and = 90.03(1).     

Microwave Dielectric Characteristics of MgTiO<Subscript>3</Subscript>/CaTiO<Subscript>3</Subscript> Layered Ceramics

MgTiO₃/CaTiO₃ layered ceramics with differently stacking were fabricated and the microwave dielectric properties were evaluated with TE₀₁₁ mode. With increasing CaTiO₃ thickness fraction, the resonant frequency decreased and the dielectric constant increased with a near-linear relation for the bi-layer ceramics, while the values of the tri-layer MgTiO₃/CaTiO₃/MgTiO₃ ceramics with thickness ratio of 1:1:1 derived much from the curves of the bi-layer ceramics. The finite element method was used to give an explanation for the differences between the bi-layer and tri-layer ceramics.     

Low operating temperature CO sensor prepared using SnO<Subscript>2</Subscript> nanoparticles

A low operating temperature CO (carbon monoxide) sensor was fabricated from a nanometer-scale SnO₂ (tin oxide) powder. The SnO₂ nanoparticles in a size range 10–20 nm were synthesized as a function of surfactant (tri-n-octylamine, TOA) addition (0–1.5 mol%) via a simple thermal decomposition method. The resulting SnO₂ nanoparticles were first screen-printed onto an electrode patterned substrate to be a thick film. Subsequently, the composite film was heat-treated to be a device for sensing CO gas. The thermal decomposed powders were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffractometry (XRD), and surface area measurements (BET). The CO-sensing performance of all the sensors was investigated. The experimental results showed that the TOA addition significantly decreased the particle size of the resulting SnO₂ nanoparticle. However, the structure of the powder coating was crucial to their sensing performance. After heat-treatment, the smaller particle tended to cause the formation of agglomeration, resulting in the decline of surface area and reducing the reaction site during sensing. However, the paths for the sensed gas entering between the agglomerated structure may influence the sensing performance. As a CO sensing material, the SnO₂ nanoparticle (~12 nm in diameter) prepared with 1.25 mol% TOA addition exhibited most stable electrical performance. The SnO₂ coating with TOA addition >0.75 mol% exhibited sensor response at a relatively low temperature of <50°C.