Dielectric Properties and Reliability of Zn0.95Mg0.05TiO3+0.25TiO2 MLCCs with Different Pd/Ag Ratios of Electrodes

In order to study the micromechanism of silver migration that influences the dielectric properties and reliability of Zn_0.95Mg_0.05TiO₃+0.25TiO₂ (ZMT") with 1 wt% 3ZnO–B₂O₃ multilayer ceramic capacitors (MLCCs), various silver (Ag)–palladium (Pd) ratios of conductors were used as inner electrodes. It was found that the electrical resistance of a MLCC sample with pure Ag as inner electrodes was degraded drastically to compared with the Ag/Pd inner electrodes at measuring temperatures ranging from 25°C to 175°C. It may be explained that the pure Ag migrates easily into the dielectric layer along the grain boundary during co-firing. The ZMT" MLCCs exhibited increasing dielectric constant and insulation resistance considerably with increasing sintering temperature. Moreover, the results also indicate that Ag diffusion changes the dielectric properties and decreases the breakdown voltage. A ZMT" MLCC with a high Ag content in the inner electrode exhibits poor reliability, and the effect of Ag⁺ migration is markedly enhanced when the activation energy of the ZMT" dielectric is considerably lowered due to the excessive formation of oxygen vacancies and the semiconducting Zn₂TiO₄ phase when Ag⁺ substitutes for Zn²⁺ during co-firing.     

Vacuum Ultraviolet Spectra of Silver in a Borosilicate Glass

Vacuum ultraviolet absorption spectra of silver dissolved in 60 mol% B₂O₃-40 mol% SiO₂ glass in oxygen, nitrogen, and oxygen–nitrogen atmospheres at 1000°, 1100°, and 1200°C were measured. Strong absorption which may be attributed to Ag⁺-complex was observed around 5.5 and 6.5 eV. It is suggested that an Ag⁺-complex/Ag⁰ redox pair exists in the glass and that this pair shows O-type redox behavior.     

Interfacial Reaction Kinetics between Silver and Ceramic-Filled Glass Substrate

Interfacial reaction kinetics between Ag and ceramic-filled glass (CFG) substrate, containing borosilicate glass, high-silica glass, and alumina, has been investigated at 850°–925°C in different atmospheres. No chemical reaction at the interface of Ag/CFG is found when firing takes place in N₂ or N₂+ 1% H₂. Fired in air, however, an interfacial reaction zone is formed at the interface of Ag/CFG with Ag⁺ ion diffusing from silver and Al³⁺ ion dissolving from CFG, and both ions are always coupled together in the reaction zone. Microstructural and chemical analyses show that the reaction zone consists of two distinct layers; one is homogeneous, and the other, heterogeneous. The homogeneous layer, which is adjacent to Ag, is uniform in microstructure with a composition rich in Ag⁺ and Al³⁺. The heterogeneous layer is not uniform in microstructure with Si-rich and Ag–Al-rich phases. The reaction zone moves toward CFG with time, forming a heterogeneous layer first and then converting into a homogenous layer when diffusion of Ag⁺ ion into the CFG becomes significant. The growth kinetics for the homogeneous layer follows a linear rate equation, whereas the heterogeneous layer, a parabolic rate equation. Activation analyses suggest that the formation of the homogeneous layer is controlled by the combination of breakage and formation of M–O bonds, but the heterogeneous layer, by the diffusion of Ag⁺ ion in the BSG.     

Voltammetric Study of Silver in a Glass Melt

The redox reaction and the oxidation state of silver in a glass melt were studied by cyclic voltammetry and chronopotentiometry between 800° and 1200°C. Silver ions in glass were reduced at a less noble potential than the rest potential of a platinum electrode. A reversible redox reaction of silver in glass was indicated from the analysis of the cyclic voltammogram. An analysis based on the electron transference number revealed that the solubility of reduced silver increased with increasing temperature. Ag⁺/Ag⁰ equilibrium in glass was suggested because the rest potential of the platinum electrode in glass was a mixed potential. No relation was observed between the redox behavior of silver in glass and optical basicity. O-type redox behavior of silver in glass was shown.     

Low-Temperature Preparation of Nanocrystalline Lead Zirconate Titanate and Lead Lanthanum Zirconate Titanate Powders Using Triethanolamine

Nanocrystalline lead zirconate titanate (PZT) powders, with a Zr:Ti ratio of 60:40, have been prepared from a solution of triethanolamine (TEA) and Ti⁴⁺, Zr⁴⁺, and Pb²⁺ ions. The metal ions were in solution through complex formation with TEA. The soluble metal-ion–TEA complex formed the precursor material when it was completely dehydrated. Heat treatment of the precursor at 450°C resulted in single-phase PZT powders. The precursor and the heat-treated powders have been characterized by using thermal analysis and X-ray diffractometry (XRD) studies. The average particle size, as measured from X-ray line broadening and transmission electron microscopy studies, was ∼20 nm. PZT powders modified with 3 mol% of lanthanum (PLZT) also were prepared through this route and were investigated via XRD studies. The dielectric constants of the PZT and PLZT powders were 12475 and 11262, and their corresponding Curie temperatures were 362° and 315°C, respectively.     

Ion Exchange in Alkali Layers of Potassium β -Ferrite ((1 + x)K2O · 11Fe2O3) Single Crystals

The potassium ions in potassium β-ferrite ((1 + x)K₂O ·11Fe₂O₃) crystals were exchanged with Na⁺, Rb⁺, Cs⁺, Ag⁺, NH₄⁺, and H₃O⁺ in molten nitrates or in concentrated H₂SO₄. On the other hand, spinel and hexagonal ferrites were formed by soaking the crystals in the melt of divalent salts. The crystals of K⁺, Rb⁺, and Cs⁺β-ferrites decomposed to form α-Fe₂O₃ at high temperatures of 800° to 1100°C. In addition, H₃O⁺, NH₄⁺, and Ag⁺β-ferrites decomposed to form α-Fe₂O₃ at relatively low temperatures of 350° to 650°C, in accordance with the stabilities of the inserted ions. The electrical properties of some β-ferrites were measured.     

Porous Glass-Ceramics with Bacteriostatic Properties in Silver-Containing Titanium Phosphates: Control of Release of Silver Ions from Glass-Ceramics into Aqueous Solution

Porous glass-ceramics with the surface phase consisting predominantly of AgTi₂(PO₄)₃ crystal and the interior phase of LiTi₂(PO₄)₃ crystal are prepared by exchange of Ag⁺ions for Li⁺ions. In the present work, the release of Ag⁺ ions from glass-ceramics into aqueous solutions was investigated. Exchanged Ag⁺ ions were chemically stable in water. The as-exchanged glass-ceramics released Ag⁺ ions of 3045 equiv/g into phosphate buffer solution containing Na⁺ ions. X-ray diffraction analysis showed that silver-containing titanium phosphate crystalline phase in the glass-ceramics did not deteriorate even by heating at 900°C. The amount released from the heated glass-ceramics into the buffer solution was found to decrease drastically by 1–2 μequiv/g. The heated glass-ceramics showed excellent bacteriostatic properties. Glass-ceramics are expected to be novel bacteriostatic materials which have high thermal resistance and are medically safe.     

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.     

Reaction and Diffusion in Silver-Arsenic Chalcogenide Glass Systems

The diffusion of Ag from the metal or Ag₂Se in amorphous As₂S₃ and As₂Se₃ at 175°C is accompanied by the reduction of As from a valence of 3+ to 2+ or 2+ to 1 + to maintain charge neutrality in the glass. Only Ag⁺ diffuses at this temperature; all other ions are essentially immobile. An amorphous reaction-product phase is formed in the diffusion zone with a composition range of 28.6 to 44.4 at % Ag. The lower limit corresponds to all As cations of 2+ valence (equivalent to amorphous Ag₂As₂S₃); the upper limit, the maximum solubility of Ag in these glasses, corresponds to all As cations of 1 + valence (equivalent to amorphous Ag₁As₂S₃). The diffusivity of Ag in these glasses at 175°C for concentrations of 10 to 35 at.% Ag is
Sulfide 4× 10⁻¹⁴ exp[(+0.23±0.01)(at.% Ag)]cm²/s
Selenide 2' 10⁻¹¹ exp[(+0.14±0.01)(at.% Ag)]cm²/s     

Effect of V2O5 Doping on the Sintering and Dielectric Properties of M-Phase Li1+x−yNb1−x−3yTix+4yO3 Ceramics

The effect of the addition of V₂O₅ on the structure, sintering and dielectric properties of M -phase (Li_{1+ x − y} Nb_{1− x −3 y} Ti _x +4 _y )O₃ ceramics has been investigated. Homogeneous substitution of V⁵⁺ for Nb⁵⁺ was obtained in LiNb_{0.6(1− x )}V_{0.6 x} Ti_0.5O₃ for x ≤ 0.02. The addition of V₂O₅ led to a large reduction in the sintering temperature and samples with x = 0.02 could be fully densified at 900°C. The substitution of vanadia had a relatively minor adverse effect on the microwave dielectric properties of the M -phase system and the x = 0.02 ceramics had [alt epsilon]_r= 66, Q × f = 3800 at 5.6 GHz, and τ_f= 11 ppm/°C. Preliminary investigations suggest that silver metallization does not diffuse into the V₂O₅-doped M -phase ceramics at 900°C, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications.     

Role of Cinnabar in Luster Production

Ancient documentation referring to the use of cinnabar in the production of luster decorations has recently been corroborated by archaeological findings. However, luster decorations do not show any trace of the use of cinnabar in their composition because the temperatures involved in luster firing (500°–600°C) result in the complete decomposition and volatilization of cinnabar. An in situ x-ray diffraction experiment was designed to clarify the role of cinnabar in the production of luster decorations. The high-energy, high-flux radiation ID15B beamline at the European Synchrotron Radiation Facility was necessary to ensure good time/temperature resolution, penetration, and high-quality data. Results show that cinnabar acts as a reducing agent for copper because it provides the formation of copper (Cu⁺) and silver (Ag⁺) sulfur-containing phases, and it inhibits the crystallization of metallic silver in the temperature range of interest in luster production. The addition of elemental sulfur also produces these phases, but at temperatures <500°C, which are not adequate for the production of copper-containing lusters.     

Fabrication of Transparent Lead Lanthanum Zirconate Titanate Ceramics from Fine Powders by Two-Stage Sintering

Transparent lead lanthanum zirconate titanate (PLZT) ceramics were fabricated from fine powders using an inexpensive two-stage sintering technique. The powders were prepared by hydrolysis from low-cost inorganic precursors. In the two-stage sintering method, uniaxially pressed green pellets were densified to nearly theoretical values in an oxygen gas atmosphere during the first-stage sintering, at 1000°C for 1 h, and then residual, free lead oxide in the pellets was removed by second-stage sintering at 1100°C for 12 h. Transparent ceramic with an average grain size of 1.6 μm and a porosity of 1.3% was obtained. The transparency and dielectric characteristics of the present samples were compared with those of hot-pressed samples: The study of the polarization–field hysteresis loops of the present samples yielded a remanent polarization of 6.8 μC/m² and a coercive field of 1.6 kV/cm. The low coercive field of PLZT ceramics could potentially reduce the driving voltage of electrooptic devices in many applications.     

Giant Permittivity of a Bismuth Zinc Niobate–Silver Composite

Bismuth zinc niobate–Silver (BZN–Ag) composites were prepared by the solid-state ceramic route. The sintering temperature of BZN–Ag composites was lowered to 850°C/2 h. The structure and surface morphology of the composites were investigated using X-ray diffraction and optical microscope. The dielectric and conducting properties of the composites were systematically investigated with the volume fraction of silver in the frequency range from 1 KHz to 1 MHz. The dielectric constant of the composite increases with the silver content and is in good agreement with the power law below the percolation limit. Addition of 0.14 volume fraction of silver increases the dielectric constant of BZN+2 wt% B₂O₃ from 150 to 2350 at 1 MHz. However, 15 volume percentage of silver loading results in a large permittivity of (ɛ_r)≈10⁵ with a low dielectric loss (tan δ≈10⁻²) at 1 MHz. Subsequent increase in silver loading decreases the dielectric constant. The BZN–B₂O₃–Ag composite with large permittivity may find applications in electromechanical and tunable devices.     

Effect of Neodymium:Yttrium Aluminum Garnet Laser Irradiation on Crystallization in Li2O–Al2O3–SiO2 Glass

A 355-nm neodymium:yttrium aluminum garnet laser, produced by a harmonic generator, was used for the nucleation process in photosensitive glass containing Ag⁺ and Ce³⁺ ions. The pulse width and frequency of the laser were 8 ns and 10 Hz, respectively. Heat treatment was conducted at 570°C for 1 h, following laser irradiation, to produce crystalline growth, after which a LiAlSi₃O₈ crystal phase appeared in the laser-irradiated Li₂O–Al₂O₃–SiO₂ glass. The present study compares the effect of laser-induced nucleation on glass crystallization with that of spontaneous nucleation by heat treatment.     

Microwave Characteristics of (Pb,Ca)(Fe,Nb,Sn)O3 Dielectric Materials

The dielectric properties of (Pb_{1− x} Ca _x ){(Fe_1/2Nb_1/2)_{1– y} Sn _y }O₃ solid solutions, where 0.4 lessthan equal tox ≤ 0.6, y = 0.05, 0.1, have been investigated at microwave frequencies. The replacement of Fe³⁺/Nb⁵⁺ by Sn⁴⁺ at the B–site of the perov-skite structure considerably improves the loss quality factor Q and does not remarkably affect the dielectric constant epsilon_r and the temperature coefficient of resonant frequency tau_f. The tau_f value of nearly 0 ppm/°C can be realized for x= 0.55. New high-quality dielectric ceramics having epsilon_r of 85.3-89.9,Qf values of 7510-8600 GHz, and τ_f of 0-9 ppm/°C were obtained at 1150°C for 3 h sintering in air. The influence of the sintering atmosphere on dielectric properties was also investigated.     

Microwave Dielectric Properties of CaTiO3-CaAl1/2Nb1/2O3 Ceramics Doped with Li3NbO4

The microwave dielectric properties of CaTi_{1− x} (Al_1/2Nb_1/2) _x O₃ solid solutions (0.3 ≤ x ≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO₃. The substitution of Ti⁴⁺ by Al³⁺/Nb⁵⁺ improved the quality factor Q of the sintered specimens. A small addition of Li₃NbO₄ (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x = 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛ_r) of 48, a Q × f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τ_f) of −2 ppm/K. Li₃NbO₄ as a sintering additive had no harmful influence on τ_f of ceramics.     

Microstructural Evolution during Pressureless Sintering of Lead Lanthanum Zirconate Titanate Ceramics with Excess Lead(II) Oxide

The early stages of sintering of lead lanthanum zirconate titanate (PLZT) 9/65/35 ^† ceramics prepared with 10 wt% excess PbO were monitored by quenching uniaxially pressed pellets after a variety of heat treatments. TEM revealed a PbO-rich amorphous film covering the particle surfaces and interparticle porosity in pellets quenched after 5 min at 1125° to 1180°C. This amorphous phase is indicative of the presence of a high-temperature liquid phase with composition approximately Pb_0.87Zr_0.15Ti_0.04O_1.19. The liquid composition moves toward the PbO-TiO₂ eutectic as sintering progresses. After 10 to 30 min at 1180°C, the liquid composition was approximately Pb_0.9Zr_0.04Yi_0.06O_l.1 and crystallized on quenching. High densities of dislocations with = 1/2〈110〉 and low-angle boundaries were observed in samples quenched from 1180°C after 10 to 30 min. Mechanisms for the formation of these dislocations are suggested.     

Characterization of Silver Interdiffusion into (Zn,Mg)TiO3+x:Bi:Sb Multilayer Ceramic Capacitor

In this study, (Zn,Mg)TiO_{3+ x} +Bi₂O₃+Sb₂O₅ multilayer ceramic capacitors (MLCCs) with different proportions of a silver (Ag)–palladium (Pd) mixture acting as the inner electrode were sintered at 925°C for 2 h to evaluate the effect of the inner electrode on reliability. The main results reveal that the lifetime is inversely proportional to the Ag content in the Ag/Pd inner electrode. Ag diffusion into the (Zn,Mg)TiO_{3+ x} +Bi₂O₃+Sb₂O₅ MLCC during cofiring at 925°C for 2 h and Ag migration at 140°C against 200 V are both responsible for the short lifetime of the (Zn,Mg)TiO_{3+ x} +Bi₂O₃+Sb₂O₅ MLCC, particularly the latter factor. A Bi,Sb-rich secondary phase was present at the triple junction and a small amount of Ag was detected from the second phase for a (Zn,Mg)TiO_{3+ x} +Bi₂O₃+Sb₂O₅ MLCC with a high Ag content in the inner electrode of Ag/Pd=99/01. However, this was not the case with a low Ag content in the inner electrode of Ag/Pd=90/10. This means that the Bi,Sb-rich second phase plays an important role in determining the degradation of insulation resistance due to the excessive formation of oxygen vacancies from the reaction of Ag⁺ for Bi³⁺ or Sb⁵⁺ substitution to lower the activation energy of the (Zn,Mg)TiO₃+Bi₂O₃+Sb₂O₅ dielectrics and to enhance markedly the effect of Ag migration.     

Structure and Mechanism of Conduction of Semiconductor Glasses

The area of glass formation in the system GeO₂-P₄O₁₀-V₂O₅ and the properties of the glasses in this area were determined. The glasses displayed electronic conduction at room temperature (25°C). Resistivity ranged from 500 ohm-cm to 10⁹ ohm-cm at 25°C. Some of the glasses had unusual negative temperature coefficients of resistance of the order of -760,000 ppm °C⁻¹ in the range 25° to -55°C. Volt-ampere characteristics indicated nonlinearity suitable for thermistor application. Other unusual properties included high refractive indices from 1.6 to >2.0 and dielectric constants from 6 to 33 at 1 Mc and 25°C. Values of loss-tangents, however, were high. Infrared spectra indicated that the V⁵⁺ ion existed in sixfold coordination in the glassy state as well as in the devitrified crystalline state. The normal vibrational frequency of the V–O bond at 1015 cm⁻¹ was observed for all glasses in the system. Property versus composition curves indicated that density, refractive index, and dielectric constant of ternary glasses in the system do not obey the additivity rule. The density versus mole % V₂O₅ curve goes through a minimum. Derived quantities from experimental data indicate pronounced influence of V₂O₅ on oxygen packing in the system. Addition of SiO₂, even in small quantities, destroys glass formation. The structure of these glasses, which differs from that of silicate glasses, is discussed. A mechanism of conduction is suggested, based on evidence from magnetic susceptibility, chemical analysis, activation energy, and infrared spectra.     

Electrical Properties of Superionic Conducting Glasses in the Pseudobinary System CuI-Cu2MoO4

Cu⁺-ion-conducting glasses were prepared in the pseudo-binary system CuI-Cu₂MoO₄. These glasses have high ionic conductivities at room temperature in the range 10⁻¹ to 10° S·m⁻¹, which are 10 to 20 times greater than those of the Ag⁺-ion-conducting glasses with the same iodide contents in the system AgI-Ag₂MoO₄. The conductivities increase with increasing CuI content. The increase in the conductivity can be explained in terms of a decrease in the activation energy for conduction. The electronic conductivity was measured by the Wagner polarization method and indicates that the transport number of Cu⁺ ions in those glasses is 0.9996 and larger.