Partial Electronic Conductivity and Chemical Diffusivity of Li<Subscript>3<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript>2/3−<Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> Solid Solution

Partial electronic conductivity and chemical diffusivity of Li have been measured on the system of Li_3xLa_2/3–xTiO₃ (LLT) with x = 0.13, a prospective Li⁺ electrolyte, against oxygen activity in the range of 10^–22 < a_O2 < 0.21 at 557, 610 and 663C, respectively by an ion-blocking polarization technique. It is found that the electronic conductivity of LLT, which in air is essentially an ionic conductor, varies as a_O2^–1/4 to render it mixed-conductive in reducing atmospheres, say, in a_O2 < 10^–12. The chemical diffusivity of component Li also increases from a value of the order of 10^–8 cm²/s in air atmosphere up to a maximum on the order of 10^–3 cm²/s as the electronic conductivity increases with decreasing oxygen activity. This is attributed to the variation of the electronic transference number and the thermodynamic factor with oxygen activity. The latter has been evaluated to be on the order of 10–10³.     

Electrical Properties of 6H-BaTi0.95M0.05O3−δ Ceramics where M = Mn, Fe, Co and Ni

Hexagonal BaTiO₃ materials have been stabilised at room temperature according to the formula BaTi_0.95M_0.05 O_3– where M = Mn, Fe, Co and Ni. Dense ceramics (> 96% of the theoretical X-ray density) were sintered at 1450C in flowing O₂ gas from calcined powders prepared by the mixed oxide route at 1300C. All samples were single-phase and the bulk conductivity, _b, measured by Impedance Spectroscopy and Q.f measured by microwave dielectric resonance methods showed a strong dependence on the type of dopant. _b at 300C was 10^–7, 10^–5.5, 10^–5.5 and 10^–4 Scm^–1 for M = Mn, Fe, Ni and Co, respectively and Q.f at 5 GHz was 7790, 6670, 2442 and 1291 GHz, for M = Mn, Fe, Ni and Co, respectively. The correlation between _b and Q.f is attributed to the presence of oxygen vacancies and/or mixed valency of the dopant ions.     

Selective Gas Detection of SnO2-TiO2 Gas Sensors

The composite, consisting of two materials with different sensing temperatures, may show the selectivity for a particular gas. In this study, the microstructural and compositional effects on the electrical conductivity and the CO and the H₂ gas sensing properties of SnO₂-TiO₂ composites were examined. SnO₂-TiO₂ composites in entire (0–100 mol%) composition range were fabricated in the form of porous pellet by sintering at 800C for 3 h. The effects of CuO-coating (or doping) on the electrical conductivity and the sensing properties to 200 ppm CO and H₂ gases were examined.With CuO-coating, SnO₂-TiO₂ composites showed the increased sensitivity to CO gas and a large difference in the sensing temperatures between CO and H₂ gases. As a result, CuO-coated SnO₂-TiO₂ composites showed the selectivity for CO gas between 100C and 190C and the selectivity for H₂ gas between 280C and 380C.     

Electrical Properties of Acceptor Doped BaTiO3

Electrical properties of acceptor (Mn, Mg or Mn+Mg)-doped BaTiO₃ ceramic have been studied in terms of oxygen vacancy concentration, various doping levels and electrical degradation behaviors. The solubility limit of Mn on Ti sites was confirmed to be close to or less than 1.0 mol%. Oxygen vacancy concentration of Ba(Ti_{0.995 –x}Mg_0.005Mn_x)O_{2.995 –y} (x = 0, 0.005, 0.01) was estimated to be 50 times greater than that of the un-doped BaTiO₃. The leakage current of 0.5 mol% Mn-doped BaTiO₃ was stable with time, which was much lower than that of the un-doped BaTiO₃. The BaTiO₃ specimen co-doped with 0.5 mol% Mg and 1.0 mol% Mn showed the lowest leakage current below 10^{– 10}A. It was confirmed that leakage currents of Mg-doped and un-doped BaTiO₃ under dc field are effectively suppressed by Mn co-doping as long as the Mn doping level is greater than Mg contents.     

Hydrothermal Preparation and Characterization of Ultra-Fine BaTiO3 Powders from Amorphous Peroxo-Hydroxide Precursor

Ultra-fine BaTiO₃ powders were hydrothermally prepared by using Ba Ti-peroxo-hydroxide precursor. Amorphous Ba Ti-peroxo-hydroxide precursor were prepared by coprecipitation of Ba(NO₃)₂ and TiCl₄ aqueous solution adding in NH₄OH aqueous solution. The phase-pure BaTiO₃ powders with a cubic perovskite structure were synthesized at temperature as low as 110_C and in the pH range of 10–12. This processing method provides a simple low temperature route for producing BaTiO₃ nanoparticles. Under a TEM image and a SAD pattern analysis, it is evident that BaTiO₃ powders had spherical shape and single crystal nature. The BaTiO₃ ceramic sintered at 1200_C for 1 h had 97% of theoretical density and a relatively high dielectric constant ( _r = 3500).     

Nanocrystalline Alkaline Earth Titanates and Their Conductivity Characteristics Under Changing Oxygen Ambients

This work presents the first systematic study of conductivity characteristics of alkaline earth titanates in the form of polycrystalline and heteroepitaxial thin films as well as nanocrystalline ceramics as a function of temperature (between 600_C and 1000_C) and continuously adjustable oxygen partial pressures ranging from 10^{– 20} bar to 1 bar. Compared to the well-known log,-log, pO₂ profiles of single crystals, the conductivity behavior of CSD-prepared, polycrystalline SrTiO₃ thin films with a feature size of about 50 nm differs radically. The most prominent characteristics are a sharp drop under reducing conditions followed by a broad plateau region. Tailored investigations on heteroepitaxial as well as polycrystalline thin films grown by PLD and especially by studies on nanocrystalline BaTiO₃ ceramics with a mean grain size of 100 nm allowed an unambiguous assignment of the described effects to the nanocrystalline morphology of the samples.     

Ferroelectric Properties of Bi3.25Nd0.75Ti3O12 Thin Films Prepared by MOD Process

Ferroelectric Bi_{4 – x}Nd_xTi₃O₁₂(BNdT) thin films with the composition (x = 0.75) were prepared on Pt/Ti/SiO₂/Si(100) substrate by metal-organic deposition. The films were annealed by various temperatures from 550 to 650C and then the electrical and structural characteristics were investigated for the application of FRAM. Electrical properties such as dielectric constant, 2Pr and capacitance were quite dependent on the thermal heat treatment. The measured 2Pr value on the BNdT capacitor annealed at 650C was 56 C/cm² at an applied voltage of 5 V. No fatigue was observed up to 8 × 10¹⁰ read/write switching cycles at a frequency of 1 MHz regardless of annealing temperatures.     

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%     

Oxygen Permeation Properties of Ceria-Ferrite-Based Composites

The oxygen flux density of Ce_0.8Gd_0.2O_1.9–x vol% MnFe₂O₄ (CGO-xMFO) composite-type ceramics membranes has been investigated. The samples and reforming catalysts were prepared by the Pechini process. For the CGO-xMFO composites, oxygen permeation was observed even at x = 3 vol%, presumably due to the presence of grain boundary phases. For CGO-15MFO, the n-type electronic conductivity was found to be dominant at 900C or higher. The thickness dependence of jO₂ revealed that surface exchange kinetics was significantly involved in the case of the membrane thickness of L < 0.5 mm. The highest oxygen flux density of 10 molcm^–2s^–1 was achieved for CGO-15MFO with the 10 mass% Ni-Pr:CeO₂ catalyst (L = 0.25 mm) at 1000C and a flow rate of 270 sccm.     

Praseodymium-Cerium Oxide as a Surface-Effect Gas Sensor

The gas sensing behavior of praseodymium doped cerium oxide (Pr_xCe_{1 – x}O₂ or PCO) has been examined for 0–1000 ppm CO or H₂ in a 10% O₂ atmosphere at temperatures ranging from 250–350_C. Total conductivity as a function of temperature suggests that oxygen diffusion kinetics are slow below approximately 350_C. Devices with x = 0.05 and 0.10 show stable, n-type gas sensing response, while those with x = 0.20 exhibit significant drift in sensor output, presumably due to bulk oxygen migration. The response to CO is significantly stronger than that to H₂ at 300_C, and at 350_C the response to H₂ is nearly zero, resulting in a CO-selective gas sensing element. Suggestions for the source of selectivity in PCO are presented.     

Microstructure of X7R Type Base-Metal-Electroded BaTiO3 Capacitor Materials Co-Doped with MgO/Y2O3 Additives

Detailed microstructure of MgO/Y₂O₃ co-doped BaTiO₃ materials were examined using transmission electron microscopy (TEM). For the 1250_C-sintered BaTiO₃ samples possessing flat K-T characteristics, which meet the X7R specification, the granular structure is complicated. Most of the grains are very small ( 150 nm) and are highly strained. The small grains contain large proportion of Y₂O₃ species and are paraelectric, whereas the large grains contain Y₂O₃ species unevenly distributed and are of core-shell structure. In contrast, for the 1300C-sintered BaTiO₃ samples, which have K-T properties slightly off the X7R specification, the grains grew larger to around 300 nm. The core-shell structured grains are seldom observed. Apparently, it is the existence of such a non-equilibrium core-shell microstructure, which renders the dielectric properties of the BaTiO₃ materials extremely sensitive to the processing parameters.     

Microstructural and High-Temperature Electrical Characterization of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>3 − δ</Subscript>

Strontium-doped lanthanum ferrites (LSF) were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), 4-point D.C. electrical conductivity and bulk property measurements. The results were compared to those of previous studies as well as selected processing conditions. The investigation focused on effects of sintering temperature, time, atmosphere (air, O₂ and N₂) and composition of La_1–xSr_xFeO_3– (x = 0.2–0.9), on the sintering behavior, microstructural development and electrical conductivity. An oxalate precipitation method was used to prepare lanthanum ferrite powders. Simultaneous thermogravimetric and differential thermal analysis (TGA/DTA) studies found calcination temperatures of 800 and 850^C were necessary to form single-phase crystalline powders, as determined by XRD. Specimens were sintered from 1300 to 1400^C with dwell times from to 2 hrs. Results from SEM/EDS analysis showed the presence of a second phase in the samples fired in air or oxygen. The second phase was not detected by x-ray diffraction due to the small amount of material present. Samples fired in nitrogen had the lowest conductivity while those fired in oxygen had the highest. A composition of x = 0.5 resulted in the highest conductivity, 352 S/cm, at an operating temperature of 550C in air. High strontium additions (x = 0.9) lowered the linear shrinkage of LSF.     

Properties of CaTi1 − x Fe x O3 − δ Ceramic Membranes

CaCO₃, TiO₂ and Fe₂O₃ were mixed in the appropriate stoichiometric quantities and calcined at 1100C for 10 h. These powder mixtures were uniaxially pressed and sintered at temperatures ranging from 1350 to 1500_C for 2 h in order to obtain dense disk-shaped samples with nominal CaTi_{1 – x}Fe_xO_3– (x = 0.05, 0.15, 0.20, 0.40 and 0.60) compositions. Dilatometry and in situ high temperature powder X-ray diffraction analysis showed a good agreement on the thermal expansion behaviour of these materials between room temperature and 1000_C. The estimated linear thermal expansion coefficient is close to 13× 10^{– 6} K^{– 1} and is little affected by composition. No evidence for surface carbonation was detected in the infrared spectra collected on samples previously annealed in CO₂ atmospheres. The oxygen permeability measured at temperatures ranging from 750 to 1000_C goes through a sharp maximum for x = 0.20. This result is interpreted by structural differences related to change from disordered to ordered oxygen vacancies. The overall performance of CaTi_0.80Fe_0.20O_3– is compared to other mixed conducting materials.     

Development of a New MnZn-Ferrite Soft Magnetic Material for High Temperature Power Applications

At power electronic applications (e.g. in automotive, lighting, electrical equipment etc.) the inductive components that consist the heart of the power transformers are made of ceramic ferromagnetic materials of the type (Mn_xZn_yFe^{2 +}_{1 – x – y})Fe^{3 +}₂O₄. Usually they are designed in such a way in order to exhibit optimum magnetic performance and electromagnetic power loss minimum at 80–100C, which is the steady state operation temperature region for most devices. However, the continuous miniaturization of electric and electronic equipment associated with a continuous increase in the density of electronic components has as unavoidable consequence the gradual shift of the steady state operation temperature to higher levels. The need is therefore becoming obvious for the development of new power soft magnetic materials optimized to operate at higher temperatures than those at which current existing materials operate. In the present work the development is described of such a new soft ferrite material having the chemical composition (Mn_0.76Zn_0.17Fe^{2 +}_0.07)Fe^{3 +}₂O₄, initial magnetic permeability of 1800 (measured at a frequency f = 10 kHz, an induction level B < 0.1 mT and a temperature T = 25C), Curie temperature of 225C and electromagnetic power losses < 350 mW/cm³ measured at a temperature of 140C, frequency of 100 kHz and a magnetic field strength of 200 mT. The material has been successfully introduced to production and is now commercially available. The largest application is offered by the automotive industry in particular for tackling high temperature operating problems arising when control is being done near the engine (near the engine electronics).     

Scaling Effect on the Dielectric Constant in Ba(Ti x Zr1−x )O3 Thin Films

Recent work on PZT and BST thin films reveal a thickness dependence of the dielectric constant for a film thickness below 100 nm. This effect is commonly attributed to an interfacial layer between the electrode and the dielectric film (dead layer). In this contribution we report on the influence of the film thickness on the dielectric constant of Ba(Ti_xZr_{1 – x})O₃ thin films with different Zr-contents (x = 0–30 at.%). The films were prepared by chemical solution deposition (CSD) with thickness between 30 and 350 nm.The electrical characterization was performed in a temperature range between 25 and 200C. Results were interpreted with respect to the formation of a serial dead layer capacitance.     

BaTiO3−δ: Defect Structure, Electrical Conductivity, Chemical Diffusivity, Thermoelectric Power, and Oxygen Nonstoichiometry

Electrical conductivity, thermoelectric power, and chemical diffusivity are the most typical, charge-and-mass transport properties of a mixed ionic electronic conductor oxide which are essentially governed by its defect structure, and the oxygen nonstoichiometry is a direct measure of its overall defect concentration. For the system of BaTiO_3–, the total electrical conductivity has been the most extensively and systematically studied as a function of oxygen partial pressure at elevated temperatures. The other properties have also been studied, but much less extensively and systematically. The electrical conductivity and thermopower were occasionally measured together on the same specimens so that mutual compatibility or consistency might be secured. But, the rest were all determined separately on the specimens of differing quality, consequently lacking in mutual consistency. It, thus, has remained hard to evaluate the canonical, defect-chemical parameters which are consistent with each and every of these defect structure-sensitive properties that were observed. Very recently the authors have determined the total conductivity, chemical diffusivity and thermoelectric power altogether on the same specimens of BaTiO_3–, and the nonstoichiometry on the same-quality specimens at temperatures of 1073 T/K 1373 over wide enough a range of oxygen partial pressure (normally, 10^–16 Po₂/atm 1) that encloses an electron/hole/ion mixed regime. In this article, we will compile all the literature data on these defect-structure-sensitive properties and extract from the authors' own, without using any ad hoc assumptions regarding, e.g., the electronic carrier mobilities and effective density of states, the basic defect-chemical parameters including defect-equilibrium constants, carrier mobilities and densities, and electronic heats of transport, which are the most consistent with the properties observed. Compared to the conventional picture of the defect structure of undoped BaTiO₃, thus, some new insights into the defect chemical nature of BaTiO_3– are provided.     

PZN-PFW and PFN-PFW Relaxor Ferroelectric Ceramics by a Reaction-Sintering Process

Pb((Zn_1/3Nb_2/3)_0.6(Fe_2/3W_1/3)_0.4)O₃ and Pb((Fe_1/2Nb_1/2)_0.7(Fe_2/3W_1/3)_0.3)O₃ (PZNFW and PFNW) perovskite ceramics prepared by a reaction-sintering process were investigated. Without any calcination, the mixture of PbO, Zn(NO₃)₂, Fe(NO₃)₃, Nb₂O₅ and WO₃ for stoichiometric PZNFW and PFNW was pressed and sintered directly. Pyrochlore phase more than 25% were formed in PZNFW ceramics after 2 h sintering at 930–980C. PFNW ceramics of 100% perovskite phase were obtained after 4 h sintering at 930–1080C. A density of 8.13 g/cm³ (93.4% of theoretical value) was obtained after sintered at 1080C for 4 h. Dielectric constant at room temperature under 1 kHz reaches 32000 after sintered at 1080C for 4 h.     

Pb((Mg0.7Zn0.3)1/3Nb2/3)O3 Relaxor Ferroelectric Ceramics by a Reaction-Sintering Process

Pb((Mg_1/3Nb_2/3)_0.7(Zn_1/3Nb_2/3)_0.3)O₃ (PMZN) relaxor ferroelectric ceramics produced by a reaction-sintering process were investigated. Without any calcination, the mixture of PbO, Mg(NO₃)₂, Zn(NO₃)₂ and Nb₂O₅ was pressed into pellets and sintered directly. PMZN ceramics of 100% perovskite phase were obtained. Density of 8.11 g/cm³ (> 98% of theoretical value) was obtained after sintered at 1200C for 2 h. 3–9 m grain size was obtained in PMZN ceramics sintered at 1180C–1250C for two hours by reaction-sintering process.Dielectric constant at room temperature under 1 kHz reaches 18200 after sintered at 1200C for 2 h.     

Preparation of Perovskite Pb(B0.5Nb0.5)O3 (B = Rare-Earth Elements)

Pb(B_0.5Nb_0.5)O₃ (B = Sc, Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) powders were prepared from mixed nitrate solutions by a chemical coprecipitation method. This method produced very small particles (30 nm) with good compositional homogeneity. These powders were highly reactive upon calcination. The powders of the systems (B = Sc, Tm, Yb and Lu) yielded 100% perovskite phase after calcination between 800C and 1000C for 1 h. For the system with B = Er, 93% perovskite phase was formed at 900C for 1 h. For the other systems of the elements (B = Y, Nd, Sm, Eu, Gd, Tb, Dy and Ho) with a larger ionic size, perovskite compounds were not formed up to 1100C. The stability and the possible formation of the compounds with a perovskite structure for the Pb(B_0.5Nb_0.5)O₃ series were discussed.     

Low Temperature Sintering of BaTi<Subscript>4</Subscript>O<Subscript>9</Subscript>-Based Middle-<Emphasis Type="Italic">k</Emphasis> Dielectric Composition for LTCC Applications

Effect of glass addition on the low-temperature sintering and microwave dielectric properties of BaTi₄O₉-based ceramics were studied to develop the middle-k dielectric composition for the functional substrate of low-temperature co-fired ceramics. When 10 wt% of glass was added, sufficient densification was obtained and the relative density more than 98% was reached at the sintering temperature of 875C. The microwave dielectric properties were k = 32, Q × f = 9000 GHz, and t_cf = 10 ppm/C. As the added amount of glass frit with base dielectric composition, phase changes from BaTi₄O₉ to BaTi₅O₁₁ and Ba₄Ti₁₃O₃₀ was observed, which result in the modification of microwave dielectric properties.