Thermal and dielectric properties of ZnO-B2O3-MO3glasses (M = W, Mo)

Glasses in the ZnO-B₂O₃-MO₃(M = W, Mo) ternary were examined as potential replacements to PbO-B₂O₃-SiO₂-ZnO glass frits with the low firing temperature (500–600^∘C) for the dielectric layer of a plasma display panels (PDPs). Glasses were melted in air at 950–1150^∘C in a narrow region of the ternary using standard reagent grade materials. The glasses were evaluated for glass transition temperature (T _g ), softening temperature (T _d ), the coefficient of thermal expansion (CTE), dielectric constant (ε _r ), and optical property. The glass transition temperature of the glasses varied between 470 and 560^∘C. The coefficient of thermal expansion and the dielectric constant of the glasses were in the range of 5–8 × 10^{− 6}/^∘C and 8–10, respectively. The addition of MO₃to ZnO-B₂O₃binary could induce the expansion of glass forming region, the reduction of T _g and the increase in the CTE and the dielectric constant of the glasses. Also, the effect of the addition of MO₃to ZnO-B₂O₃binary on the transmittance in the visible-light region (350–700 nm) was investigated.     

The effect of alumina addition on the electrical conductivity of Gd-doped ceria

Acceptor doped-ceria is a possible electrolyte material for the IT-SOFC (intermediate temperature solid oxide fuel cell) due to its high oxygen-ion conductivity. However, its use has been limited by its mechanical weakness and the appearance of electronic conductivity in reducing condition. In this study, alumina was selected as an additive in the doped-ceria to see if it increases the oxygen-ion conductivity and mechanical strength. Effects of alumina addition in doped ceria were studied as a function of alumina content and acceptor (Gd) content. The electrical conductivity of (Ce_1−x Gd _x O_2−δ)_1−y + (Al₂O₃) _y (x = 0–0.35, y = 0–0.10) was measured by using impedance spectroscopy. The grain conductivity of Ce_0.8Gd_0.2O_2-δ (GDC20) with 5 mol% alumina increased ∼3 times from that of GDC20 at 300^∘C. The grain conductivity was even ∼2 times higher than that of Ce_0.9Gd_0.1O_2−δ (GDC10) at 300^∘C. The electrical conductivity of GDC20 without alumina addition, measured at 500^∘C in air, rapidly decreased after exposure to reducing condition (Po₂∼10⁻²² atm) at 800^∘C. However, the decrease was much slower in GDC20 with alumina addition, indicating the improved mechanical strength. Among the examined compositions, (Ce_0.75Gd_0.25 O_2-δ)_0.95 + (Al₂O₃)_0.05 (GDC25A5) showed the highest conductivity at most temperatures.     

Defects and transport in Gd-doped BaPrO3

The electrical conductivity of BaPr_1−x Gd_xO_3−δ has been characterized by means of the four-point van der Pauw technique at 200–1100 °C as a function of pO₂ and pH₂O. The contributions from ionic charge carriers were investigated by the EMF of concentration cells and the H⁺/D⁺ isotope effect on the total conductivity. BaPr_1−x Gd _x O_3−δ is predominately a p-type electronic conductor under oxidizing conditions, while ionic conduction is barely measurable. Gd(III) substituted for Pr(IV) is charge compensated mainly by electron holes, with protons and oxygen vacancies contributing significantly but as minority defects only at low temperatures (wet conditions) and at high temperatures, respectively. The conductivity behaviour has been modelled under these assumptions to extract thermodynamic parameters for the defect reactions at play. The practical use of this material is limited by its poor chemical stability.     

Changes in proton transverse relaxation times of rat myocardium that has suffered a previous oxidative insult

An oxidative insult can induce severe damage, as in the phenomenon of myocardial ischemia and reperfusion. However, there are situations in which the damage is not so obvious (e.g., silent ischemia or aging), and the negative effects will be seen only in time. Our aim was to reveal these small changes in the myofilaments by using the nuclear magnetic resonance (NMR) technique. We used Wistar rat hearts in a constant-pressure Langendorff system, perfused with oxygenated Krebs-Henseleit buffer at 37°C. After 15 minutes of stabilization, the hearts were perfused with buffer supplemented with H₂O₂ at 50, 75, or 100 μmol/L for 15 or 30 minutes. Fifteen-minute and 45-minute perfusion controls and unperfused hearts were also collected. Heart rate (HR) and left ventricular developed pressure (LVDP) were determined with the help of a latex balloon, inserted in the left ventricle and connected with a pressure transducer. Proton transverse relaxation times (T ₂) were determined at the end of the experiment.T ₂ values were measured again in the same tissue fragments after they had been glycerinated and incubated in relaxation and rigor media. The functional parameters (HR, LVDP, coronary flow) were not significantly changed in control and 50 μmol/L H₂O₂ groups but were increased in the 75 μmol/L H₂O₂ group and significantly decreased in the 100 μmol/L H₂O₂ group.T ₂ is significantly decreased in rigor media starting with 50 μmol/L H₂O₂ administrated for 30 minutes and does not correlate with dose and duration of the oxidative insult.T ₂ in rigor is shorter than in relaxation media within the groups, and this difference is increased in the treated hearts.     

Control of Microwave Dielectric Properties in the System BaO ⋅ Nd<Subscript>2</Subscript>O<Subscript>3</Subscript> ⋅ 4TiO<Subscript>2</Subscript>—BaO ⋅ Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ⋅ 4TiO<Subscript>2</Subscript>

BaO ⋅ Nd₂O₃ ⋅ 4TiO₂—based ceramics were prepared by the mixed oxide route. Specimens were sintered at temperatures in the range 1200–1450^∘C. Microstructures were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM); microwave dielectric properties were determined at 3 GHz by the Hakki and Coleman method. Product densities were at least 95% theoretical. The addition of up to 1 wt% Al₂O₃ to the starting mixtures reduced the sintering temperatures by at least 100^∘C. Incorporation of small levels of Al into the structure (initially Ti sites) led to an increase in Q × f values, from 6200 to 7000 GHz, a decrease in relative permittivity (ε_r) from 88 to 78, and moved the temperature coefficient of resonant frequency (τ_f) towards zero. The addition of 0.5 wt% Al₂O₃ with 8 wt% Bi₂O₃ improved densification, increased both ε_r (to 88) and Q× f (to 8000 GHz) and moved τ_f closer to zero. Ceramics in the system (1 − x)BaO ⋅ Nd₂O₃ ⋅ 4TiO₂ + xBaO ⋅ Al₂O₃ ⋅ 4TiO₂ exhibited very limited solid solubility. The end member BaO ⋅ Al₂O₃ ⋅ 4TiO₂ was tetragonal in structure with the following dielectric properties: ε_r = 35; Q× f = 5000 GHz; τ_f = −15ppm/^∘C. Microstructures of the mixed Nd-Al compositions contained two distinct phases, Nd-rich needle-like grains and large Al-rich, lath-shaped grains. Products with near zero τ_f were achieved at compositions of approximately 0.14BaO ⋅ Nd₂O₃ ⋅ 4TiO₂ + 0.86BaO ⋅ Al₂O₃ ⋅ 4TiO₂, where Q× f = 8200 GHz and ε_r = 71.     

Preparation of SnO2 whiskers via the decomposition of tin oxalate

A new method for preparing SnO₂ whiskers by the decomposition of SnC₂O₄ is suggested. A Whisker-like morphology of a SnC₂O₄ precipitate was attained via the gradual addition of an oxalic acid solution to a hot SnCl₂ aqueous solution (T > 50^∘C). In comparison, when the solution temperature was either lower than 50^∘C or when ethanol was used as the solvent, the SnC₂O₄ precipitate showed an angular and relatively isotropic morphology. The morphology of the SnC₂O₄ precipitate remained even after its thermal decomposition into SnO₂ at 400^∘C indicating that SnC₂O₄ precipitation is a key step in preparing the whiskers. The formation mechanism of SnO₂ whiskers was explained by the supersaturation during the precipitation of SnC₂O₄.     

Effects of molten salt synthesis (MSS) parameters on the morphology of Sr3Ti2O7 and SrTiO3 seed crystals

A two-step molten salt synthesis process was utilized to fabricate Sr₃Ti₂O₇ and SrTiO_3. High aspect ratio SrTiO₃ seed crystals were developed by optimizing processing conditions such as temperature, salt-to-oxide ratio, and flux type in a systematic fashion. Sr₃Ti₂O₇ seeds were synthesized at temperatures ranging from 1050–1350°C, using salt-to-oxide ratios of 3:1, 1:1, and 1:3, and various salt types, including NaCl, KCl, and a 1:1 combination of NaCl and KCl. Sr₃Ti₂O₇ seeds synthesized at 1250°C with a 1:1 salt-to-oxide ratio in 100% NaCl salt resulted in a majority of higher aspect ratio platelets and elongated platelets as opposed to lower aspect ratio cubic-like and tetragonal-like morphologies. The seeds were 10–40 μm in length with aspect ratios of highly elongated platelets as high as 25:1. A second MSS step was used to synthesize SrTiO₃ seeds of the proper composition by TiO₂ addition to the Sr₃Ti₂O₇ seeds and heat treatment at 1100°C. These studies showed that highly anisotropic SrTiO₃ seeds could be produced at 1250°C using a 1:1 salt-to-oxide ratio in 100% NaCl flux. XRD studies of the resulting SrTiO₃ seeds revealed that the increase in aspect ratio for these particular seeds also resulted in the enhancement of (200) peaks, which are of major interest for texturing of PMN-PT.     

Quantitative T 2 measurement of a single voxel with arbitrary shape using pinwheel excitation and CPMG acquisition

Objective The aim of this study is to present a new approach for making quantitative single-voxel T ₂ measurements from an arbitrarily shaped region of interest (ROI), where the advantage of the signal-to-noise ratio (SNR) per unit time of the single-voxel approach over conventional imaging approach can be achieved. Materials and methods Two-dimensional (2D) spatially selective radiofrequency (RF) pulses are proposed in this work for T ₂ measurements based on using interleaved spiral trajectories in excitation k-space (pinwheel excitation pulses), combined with a summed Carr–Purcell Meiboom–Gill (CPMG) echo acquisition. The technique is described and compared to standard multi-echo imaging methods, on a two-compartment water phantom and an excised brain tissue. Results The studies show good agreement between imaging and our method. The measured improvement factors of SNR per unit time of our single-voxel approach over imaging approach are close to the predicted values. Conclusion Measuring T ₂ relaxation times from a selected ROI of arbitrary shape using a single-voxel rather than an imaging approach can increase the SNR per unit time, which is critical for dynamic T ₂ or multi-component T ₂ measurements.     

Dielectric behavior of Bi2/3Cu3Ti4O12 ceramic and thick films

The paper reports on synthesis, sintering and microstructure of Bi_2/3Cu₃Ti₄O₁₂, a lead-free, high-permittivity material with internal barrier layer capacitor behavior. Complex impedance and capacitance of the ceramic and thick films were studied as a function of frequency (10 Hz–2 MHz) and temperature (−170 to 400°C). Dc electrical conductivity of the samples was measured in the temperature range 20–400°C. Broad and high maxima of dielectric permittivity versus temperature plots were observed reaching 60,000 for ceramic and 5,000 for thick films. The maxima decrease and shift to higher temperatures with increasing frequency. Two arcs ascribed to grains and grain boundaries were found in the plots of imaginary part versus real part of impedance. Analysis of the impedance spectra indicates that Bi_2/3Cu₃Ti₄O₁₂ ceramic could be regarded as electrically heterogeneous system composed of semiconducting grains and less conducting grain boundaries. The developed thick film capacitors with dielectric layers based on Bi_2/3Cu₃Ti₄O₁₂ exhibit dense microstructure, good cooperation with Ag electrodes, high permittivity up to 5,000 and relatively low temperature coefficient of capacitance in the temperature range 100–300°C. Broad maxima in the dielectric permittivity versus temperature curves may be attributed to Maxwell–Wagner relaxation.     

Synthesis and properties of ferroelectric Si-doped (Bi, Nd)4Ti3O12 thin films by chemical solution deposition

Ferroelectric Si-doped (Bi,Nd)₄Ti₃O₁₂ thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates through metal-organic compounds by the chemical solution deposition. The Bi_3.25Nd_0.75Ti_2.9Si_0.1O₁₂ (BNTS) precursor films were found to crystallize into the Bi-layered perovskite Bi₄Ti₃O₁₂ single-phase above 600^∘C. The synthesized BNTS films revealed a random orientation having a strong 117 reflection. The BNTS thin films prepared between 600^∘C and 700^∘C showed well-saturated P-E hysteresis loops with P _r of 13–14 μ C/cm² and E _c of 100–110 kV/cm at an applied voltage of 5 V. The surface roughness of the BNTS thin films was improved by Si doping compared with that of undoped Bi_3.35Nd_0.75Ti₃O₁₂ films.     

Low-temperature sintering and electrical properties of (1−x)Pb(Zr0.5Ti0.5)O3-xPb(Cu0.33Nb0.67)O3 ceramics

Electrical properties and sintering behaviors of (1 − x)Pb(Zr_0.5Ti_0.5)O₃-xPb(Cu_0.33Nb_0.67)O₃ ((1 − x)PZT-xPCN, 0.04 ≤ x ≤ 0.32) ceramics were investigated as a function of PCN content and sintering temperature. For the specimens sintered at 1050^∘C for 2 h, a single phase of perovskite structure was obtained up to x = 0.16, and the pyrochlore phase, Pb₂Nb₂O₇ was detected for further substitution. The dielectric constant (ε _r), electromechanical coupling factor (K_p) and the piezoelectric coefficient (d ₃₃) increased up to x = 0.08 and then decreased. These results were due to the coexistence of tetragonal and rhombohedral phases in the composition of x = 0.08. With an increasing of PCN content, Curie temperature (T_c) decreased and the dielectric loss (tanδ) increased. Typically, ε_r of 1636, K_p of 64% and d₃₃ of 473pC/N were obtained for the 0.92PZT-0.08PCN ceramics sintered at 950^∘C for 2 h.     

Aqueous urea as a model system for bi-exponential relaxation

Object To evaluate the utility of aqueous urea, doped inner- and outer-sphere relaxation agents, as an adjustable two-component model system. Materials and Methods T₂ was measured from 12 molal urea mixtures at pH 7.0 with varying amounts of the MnCl₂ and FeO_1.44 (Feridex^®, Berlex Inc, Montville, NJ). Results Bi-exponential relaxation was observed, with rates that were bilinearly related to [MnCl₂] and [FeO_1.44]. FeO_1.44 had comparable relaxivities on both urea and water, while MnCl₂ relaxivity was >  15x larger for water than for urea. Conclusion Aqueous urea, doped with inner- and outer-sphere contrast agents, is a two-compartment model system, which can be exhibit a wide range of different T₂s and signal fractions.     

Effect of Sb2O3 addition on the varistor characteristics of ZnO-Bi2O3-ZrO2-MtrO (Mtr = Mn, Co)

Effect of Sb₂O₃ addition on the varistor characteristics of pyrochlore-free ZnO-Bi₂O₃-ZrO₂-M_trO (M_tr = Mn, Co) system previously proposed has been studied. With Sb₂O₃ up to 0.1 mol%, a gradual enhancement of densification and the grain growth inhibition were seen in the system sintered between 900 and 1200^∘C. In X-ray diffraction patterns, small amount of pyrochlore appeared in the specimens doped with Sb₂O₃ (>0.06 mol%), which is thought responsible for the sintering behavior. Enhanced values of non linear coefficient (α) were obtained in ZnO-Bi₂O₃-ZrO₂ (ZBZ) doped with 0.001 mol% Sb₂O₃, but was leveled off at higher concentrations. In ZBZ added with M_trO (M_tr = Mn, Co), significant increase of nonlinear coefficient (α > 30) along with low leakage current (I _L ≪ 100 μA/cm²) was attained. The α-enhancement effect of Sb₂O₃, however, was not observed in high-α ZBZ added with M_trO. As for degradation, addition of a trace amount (0.001 mol%) of Sb₂O₃ to ZBZM_tr was efficient, especially in I _L.     

Low temperature sintering and microwave dielectric properties of Ba3Ti5Nb6O28 with B2O3 and CuO additions

The low sintering temperature and the good dielectric properties such as high dielectric constant (ε _r ), high quality factor (Q × f), and small temperature coefficient of resonant frequency (TCF) are required for the application of chip passive components in wireless communication low temperature co-fired ceramics (LTCC). In the present study, the sintering behaviors and dielectric properties of Ba₃Ti₅Nb₆O₂₈ ceramics were investigated as a function of B₂O₃-CuO content. The pure Ba₃Ti₅Nb₆O₂₈ system showed a high sintering temperature (1250^∘C) and had the good microwave dielectric properties: Q × f of 10,600 GHz, ε _r of 37, TCF of −12 ppm/^∘C. The addition of B₂O₃-CuO was revealed to lower the sintering temperature of Ba₃Ti₅Nb₆O₂₈, 900^∘C and to enhance the microwave dielectric properties: Q × f of 32,500 GHz, ε _r of 40, TCF of 9 ppm/^∘C. From the X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD) studies, these phenomena were explained in terms of the reduction of oxygen vacancies and the formation of secondary phases having the good microwave dielectric properties.     

Effect of B2O3 and CuO on the sintering temperature and microwave dielectric properties of the BaTi4O9 ceramics

The effect of B₂O₃ and CuO on the sintering temperature and microwave dielectric properties of BaTi₄O₉ ceramics was investigated. The BaTi₄O₉ ceramics were able to be sintered at 975^∘C when B₂O₃ was added. This decrease in the sintering temperature of the BaTi₄O₉ ceramics upon the addition of B₂O₃ is attributed to the formation of BaB₂O₄ second phase whose melting temperature is around 900^∘C. The B₂O₃ added BaTi₄O₉ ceramics alone were not sintered below 975^∘C, but were sintered at 875^∘C when CuO was added. The formation of BaCu(B₂O₅) second phase could be responsible for the decrease in the sintering temperature of the CuO and B₂O₃ added BaTi₄O₉ ceramics. The BaTi₄O₉ ceramics containing 2.0 mol% B₂O₃ and 5.0 mol% CuO sintered at 900^∘C for 2 h have good microwave dielectric properties of ε_r = 36.3, Q× f = 30,500 GHz and τ_f = 28.1 ppm/^∘C     

Control of 0.2CaTiO3-0.8Li0.5Nd0.5TiO3 microwave dielectric ceramics by additions of Bi2Ti2O7

Ceramics of 0.2CaTiO₃-0.8Li_0.5Nd_0.5TiO₃) have been prepared by the mixed oxide route using additions of Bi₂O₃-2TiO₂ (up to 15 wt%). Powders were calcined 1100^∘C; cylindrical specimens were fired at temperatures in the range 1250–1325^∘C. Sintered products were typically 95% dense. The microstructures were dominated by angular grains 1–2 μm in size. With increasing levels of Bi₂O₃-2TiO₂ additions, needle and lath shaped second phases developed. For Bi₂Ti₂O₇ additions up to 5 wt%, the relative permittivity increased from 95 to 131, the product of dielectric Q value and measurement frequency increased from 2150 to 2450 GHz and the temperature coefficient of resonant frequency (τ _f ) increased from −28pp/^∘C to +22pp/^∘C. A product with temperature stable τ _f could be obtained at ∼2 wt% Bi₂Ti₂O₇ additions. For high levels of additives, there is minimal change in relative permittivity, the Qxf values degrade and τ _f becomes increasingly negative.     

Sintering and compositional effects on the microwave dielectric characteristics of Mg(Ta1−x Nb x )2O6 ceramics with 0.25 ≦ x ≦ 0.35

1,500 °C−sintered MgTa₂O₆ ceramic exhibits microwave dielectric characteristics of ɛ _r = 30.5, Q × f = 56,900 GHz, and τ _f = 28.3 ppm/°C, whereas 1,400 °C-sintered MgNb₂O₆ ceramic exhibits microwave dielectric characteristics of ɛ _r = 21.7, Q × f = 89,900 GHz, and τ _f = −68.5 ppm/°C. In order to find the dielectric resonators with τ _f value close to 0 ppm/°C, the effects of sintering condition and composition on the microwave dielectric characteristics of Mg(Ta_1−x Nb _x )₂O₆ ceramics (0.25 ≦ x ≦ 0.35) prepared under sintering temperature of 1,300–1,450 °C are investigated. The results show that as the sintering temperature increases from 1,300 to 1,450 °C, the ɛ _r, Q × f and τ _f values of Mg(Ta_1−x Nb _x )₂O₆ ceramics all increase and saturate at 1,450 °C. On the other hand, as the Nb₂O₅ content decreases, the τ _f values of Mg(Ta_1−x Nb _x )₂O₆ ceramics will shift to near 0 ppm/°C. The optimized sintering conditions and composition to obtain the Mg(Ta_1−x Nb _x )₂O₆ dielectrics with τ _f close to 0 ppm/°C are sintering temperature of 1,450 °C, sintering duration of 4 h, and composition of x = 0.25, which exhibits the microwave dielectric characteristics of ɛ _r = 27.9, Q × f = 33,100 GHz, and τ _f = −0.7 ppm/°C.     

Preparation and characterization of LiNi0.80Co0.20– x Al x O2 as cathode materials for lithium ion batteries

LiNi_0.80Co_{0.20− x} Al _x O₂ samples (x = 0.025, 0.050 and 0.100) were prepared by a solid-state reaction at 725^∘C for 24 h from LiOH⋅H₂O, Ni₂O₃, Co₂O₃ and Al(OH)₃ under oxygen flow. LiNiO₂ simultaneously doped by Co-Al has been tried to improve the cathode performance. The results showed that substitution of optimum amount Al and Co at the Ni-site in LiNiO₂ improved cycling performance. As a consequence, LiNi_0.80Co_0.15Al_0.05O₂ has 178.2 mAh/g of the first discharge capacity and 174.0 mAh/g after 10 cycles. Differential capacity vs. voltage curves indicated that the Co-Al co-doped LiNiO₂ showed suppression of the phase transitions compared with pure LiNiO₂.     

Electromechanical Properties and Morphotropic Phase Boundary of Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3-BaTiO3 Lead-free Piezoelectric Ceramics

The crystal structure and electromechanical properties of two ternary ceramic Na_0.5Bi_0.5TiO₃- K_0.5Bi_0.5TiO₃-BaTiO₃ (NBT-KBT-BT) systems were investigated. A gradual change in crystalline structure and microstructure with the increase of KBT and BT concentrations were observed. It was ascertained that the rhombohedral-tetragonal morphtropic phase boundary (MPB) lies in the range of 0.024 ≰ x ≰ 0.030 for (1–5x) NBT-4x KBT-x BT system and 0.025 ≰ y ≰ 0.035 for (1 − 3y) NBT—2y KBT—y BT system at room temperature. The piezoelectric constant d₃₃ and electromechanical coupling factor k_p of the ceramics attain a maximum value of 150 pC/N and 0.298, respectively. The MPB phase diagram of NBT-KBT-BT ternary system was determined by phase analysis of XRD patterns from calcined specimens. The ferroelectric properties of the (1 − 5x) NBT—4x KBT—x BT system have been characterized. The ternary system ceramics have relatively high Curie temperature T_c.     

The effect of Co addition on the electrical conductivity of Sr- and Mg-doped LaAlO3

Co was added to see its effect on the electrical conductivity of Sr- and Mg-doped LaAlO₃ (La_0.9Sr_0.1 Al_0.9Mg_0.1O₃, LSAM). Electrical conductivities of La_0.9Sr_0.1(Al_0.9Mg_0.1)_{1− x}Co_xO₃ (LSAMC) for x = 0–0.20 were measured using 2-probe a.c. and 4-probe d.c. method at temperature between 300 and 1300^∘C in air, and as a function of Po ₂ (1–10⁻¹⁵ atm) at 1200^∘C. Electrical conductivities in air increased with increasing Co content, while their activation energy decreased. From the impedance spectroscopy analysis, it was found that both the grain and the grain boundary conductivities of LSAMC samples increased rapidly with Co-addition. LSAMC samples were oxygen ion conductors in low Po₂ and mixed conductors in high Po ₂ up to x = 0.1 just like LSAM. With Co-doping, p-type conductivities increased, however, ionic conductivities remained nearly constant.