In this study, the relationship between the microstructure and electrical conductivity of doped lanthanum gallate was investigated to identify the origin of the relatively high resistivity of the grain boundaries in this ceramic solid electrolyte. LaGaO3 containing acceptor dopants, Sr and Mg, was chemically synthesized and consolidated by field-assisted sintering technology. The relative density achieved 98% upon sintering at 1200 °C, and no intragrain porosity was found. The microstructure consisted of submicron-sized grains and exhibited a predominantly transgranular fracture mode. Structural characterization evidenced that all sintered samples display the characteristic orthorhombic crystal structure. Rietveld analysis revealed a secondary phase content of only ~0.71% in samples sintered at 1200 °C. In addition, Raman spectra revealed only the allowed characteristic vibrational modes expected for doped lanthanum gallate. The electrical conductivity was determined by impedance spectroscopy analysis. The bulk conductivity of sintered samples was found to be independent of the sintering temperature. Analysis of the grain boundary resistivity revealed a dependence on the mean grain size, which constricts the pathway of the charge carriers, leading to the formation of space charge layers. The total activation energy determined for conduction is 0.94 eV.

The electrical and dielectric properties of titanium dioxide containing erbium and praseodymium oxides as acceptors, and tantalum oxide as donor dopants were investigated aiming to identify the effects of different dopants on the dielectric properties. Dense samples with 1 mol% total co-dopants were prepared by the solid-state synthesis method, followed by conventional sintering at 1450 degrees C. A secondary phase, Er2Ti2O7, was found in some of the prepared samples. Impedance spectroscopy spectra of the samples are similar, with an average activation energy for interface conduction of about 0.27 +/- 0.05 eV, except for the sample with excess Ti, (Er0.5Ta0.5)(0.01)Ti1.09O2, (0.38 +/- 0.05 eV). All samples exhibit colossal permittivity (>10(4)) in wide temperature and frequency ranges. Erbium oxide was found to be more effective in increasing the electric permittivity of TiO2 than praseodymium oxide. Excess titanium leads to a larger grain size, and decreases both the permittivity and the dissipation factor of titanium dioxide.

Porous La2MoWO9 (W-LAMOX) impregnated with a eutectic mixture of lithium, sodium, and potassium carbonate (LNKC) ceramic membranes was synthesized and evaluated for carbon dioxide (CO2) sensing applications. Structural, microstructural, and electrical characterizations were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), and impedance spectroscopy. The results indicate that sintered thinner membranes, prepared by the tape casting method, exhibit faster and more reproducible responses to CO2 exposure than sintered thick pressed pellets. These findings highlight the potential of these composite membranes for application in CO2 sensing technologies.

This work explores the impact of the sintering temperature and co-dopant contents on the microstructure and dielectric properties of (Y0.5Nb0.5)xTi1−xO2 (0.025 ≤ x ≤ 0.10) ceramics synthesized by the solid state reaction method. The physical mechanism underlying the colossal electric permittivity was systematically investigated with experimental methods and first principles calculations. All specimens exhibited the characteristic tetragonal structure of rutile, besides secondary phases. A niobium- and yttrium-rich secondary phase emerged at the grain boundaries after heating at 1500 °C, changing the main sintering mechanism. The highest value of the electric permittivity (13499 @ 60 °C and 10 kHz) was obtained for (Y0.5Nb0.5)0.05Ti0.95O2 sintered at 1480 °C, and the lowest dissipation factor (0.21@ 60 °C and 10 kHz) for (Y0.5Nb0.5)0.1Ti0.90O2 sintered at 1500 °C. The dielectric properties of Y3+ and Nb5+ co-doped TiO2 are attributed to the internal barrier layer capacitance (IBLC) and electron-pinned dipole defect (EPDD) mechanisms.

Light-emission data were collected before, during, and after the occurrence of the flash event in pressureless electric-field-assisted (flash) sintering experiments on ZrO2: 8 mol% Y2O3 (8YSZ) and CeO2: 20 mol% Sm2O3 (20SDC) ceramic green pellets to analyze the luminescent emission from the samples. The experiments were performed at 800 °C with an applied electric field of 100 V·cm−1 at 1 kHz, limiting the electric current to 1 A. Luminescence data were obtained in the 200–1200 nm (ultraviolet–visible–near-infrared) range. The deconvolution of the optical spectra allowed for the identification of emission bands in the visible range due exclusively to the samples. The wavelength maxima of the emission bands in 8YSZ were found to be different from those in 20SDC. It is suggested that these bands might originate from the interaction of the electric current, resulting from the application of the electric field, with the depleted species located at the space-charge region at the grain boundaries of these ceramics. The main results represent a contribution to help to clarify the mechanisms responsible for the fast densification with inhibition of grain growth in electroceramics.

ZrO2:3 mol % Y2O3 (3YSZ) ceramic powders were thoroughly mixed with poly(methyl methacrylate) (PMMA), pressed into pellets, and subjected to heat treatment to prepare porous ceramics with high skeletal density by thermally removing PMMA. The porous 3YSZ pellets were first impregnated with a molten eutectic (Na,K)(2)CO3 (NKC) composition at 710 degrees C, followed by cooling to 420 degrees C for impregnation with a molten eutectic (Li,Na,K)(2)CO3 (LNKC) composition. The presence of sodium and potassium was evaluated by performing energy-dispersive X-ray analyses on the surfaces of triple-layer membranes. Permeation measurements were performed by using a homemade gas permeation setup. Electrical conductivity of carbon dioxide ions across the pellet thickness was measured at 475 degrees C for over 200 h by using impedance spectroscopy. No significant degradation of the electrical conductivity profile was observed during the test period, suggesting that the solid NKC layer acted as a protective barrier, preventing interaction between the 3YSZ ceramic and molten LNKC within the pore network.

The main dielectric properties of several ceramic materials having niobium in their composition, proposed to take part in 5G telecommunication devices, are reviewed. A preliminary basic presentation of 5G systems, the requirements for implementing their use, a concise review of the ceramic compositions containing niobium that have been studied thus far, and an evaluation of their performance are detailed. A survey is presented, including more than 80 different compositions containing niobium, focusing on key parameters, such as dielectric constant, quality factor, temperature coefficient, and sintering temperature. These parameters play a role for assessing the potential application of these ceramics in 5G devices.

This work reports a systematic study on the microstructure, electrical conductivity, and nanoindentation of 8 mol% yttria-stabilized zirconia (8YSZ), La0.9Sr0.1Ga0.8Mg0.2O3-delta (LSGM) in both pure form and as composites. The main purpose was to evaluate the effects of the minor phase on the properties of the composite materials. Commercial 8YSZ was the major phase. Pure LSGM and composites consisting of 1, 10, and 20 wt.% LSGM were prepared by the solid-state reaction method. Sintering experiments were carried out from 1200 degrees C to 1450 degrees C. The temperature of maximum shrinkage decreased with increasing LSGM content. The average grain size of the composites was dependent on the relative proportion of the minor phase. Interface reactions occurr during sintering. Electrical conductivity of the composites was found to be lower compared to that of 8YSZ. The hardness showed no significant variation with the minor phase content, although a beneficial effect on the elastic modulus was noted for composites containing 10 wt.% LSGM.

An experimental setup for the evaluation of permeation of gaseous species with the possibility of simultaneously collecting electrochemical impedance spectroscopy data in disk-shaped ceramic membranes was designed and assembled. It consists of an alumina sample holder with thermocouple tips and platinum electrodes located close to both sides of the sample. Water-cooled inlet and outlet gas connections allowed for the insertion of the sample chamber into a programmable split tubular furnace. Gas permeation through a ceramic membrane can be monitored with mass flow controllers, a mass spectrometer, and an electrochemical impedance analyzer. For testing and data validation, ceramic composite membranes were prepared with the infiltration of molten eutectic compositions of alkali salts (lithium, sodium, and potassium carbonates) into porous gadolinia-doped ceria. Values of the alkali salt melting points and the permeation rates of carbon dioxide, in agreement with reported data, were successfully collected.

Single-phase tungsten-doped lanthanum molybdenum oxide (La2MoWO9) ceramic powders were synthesized using the complex polymerization technique. Porous ceramic pellets were obtained by thermally removing graphite, which served as a pore former. The porous pellets were then impregnated with molten eutectic lithium-sodium-potassium carbonates. The energy dispersive X-ray analysis and scanning electron microscopy (FEG-SEM) images of the external and fracture surfaces of the La2MoWO9-(Li,Na,K)2CO3 composite dual-phase membrane revealed the percolation of the carbonate mixture through the pores. Electrochemical impedance spectroscopy measurements conducted at temperatures below and above the melting point of the eutectic carbonate composition demonstrated the contributions of oxygen and carbonate ions to the ionic conductivity of the dual membrane. The electrical conductivity of the carbonate ions within the membrane was continuously monitored for over 1300 h with negligible degradation, implying that the membrane could be used for long-term monitoring of CO2 without aging effects. A comparison of FEG-SEM images taken before and after this endurance test suggested minimal fouling, indicating that the membrane could potentially replace similar zirconia- and ceria-based composite membranes.

Molten Na2CO3-K2CO3 (NKC, 56-44 mol%) eutectic compositions were vacuum-impregnated, at the eutectic temperature, into two porous ZrO2:8.6 mol% MgO (magnesium-partially stabilized zirconia, MgPSZ) and ZrO2:8 mol% Y2O2 (yttria-fully stabilized zirconia, 8YSZ) ceramics. Thermogravimetric analyses were performed in mixtures of that composition with MgPSZ and 8YSZ ceramic powders. Before impregnation, porosity was achieved in the two compounds by addition and thermal removal of 30 vol.% NKC. To ascertain the carbonates had filled up through the ceramic body, both sides of the parallel and fracture surfaces of the disk-shaped impregnated compositions were observed in a scanning electron microscope and analyzed by energy-dispersive X-ray spectroscopy. The electrical conductivity of the two ceramics, before and after impregnation, was evaluated by electrochemical impedance spectroscopy in the 5 Hz-13 MHz frequency range from approximately 530 to 740 degrees C. The permeation of the carbonate ions through the membranes via the eutectic composition was assessed by the threshold temperatures of the onset of the carbonate ion percolation. The objectives were to prepare dual-phase membranes for the separation of carbon dioxide and for the development of carbon dioxide sensors.

8 mol% Y2O3-stabilized ZrO2 (8YSZ) ceramics were prepared with KCl and LiF additions to obtain porous specimens with high skeletal density. Thermogravimetric and differential thermal analyses (TG/DTA) were carried out on 8YSZ and on 8YSZ mixed to 5 wt.% KCl or 5 wt.% LiF as sacrificial pore formers that were thermally removed during sintering. The melting and evaporation of the alkali halides were evaluated by differential thermal analysis. Dilatometric analysis was also carried out following the same TG/DTA temperature profile with results suggesting rearrangement of the 8YSZ particles during LiF and KCl melting. The dilatometric data of 8YSZ green pellets mixed to KCl or LiF exhibited an initial expansion up to the melting of the alkali halide, followed by shrinkage due to sintering evolution with grain growth and pore elimination. The time that the alkali halide molten phase was kept during sintering was found to be an important parameter for obtaining 8YSZ-sintered specimens with specific pore content; bulk density and open porosity could then be tuned by controlling the time the alkali halide remained liquid during sintering. Scanning electron microscopy images of the pellet fracture surfaces showed pores that contributed to increasing the electrical resistivity as evaluated by impedance spectroscopy analysis.

The influence of small amounts of tantalum oxide as co-dopant on phase transformation and stabilization, microstructure and ionic conductivity of zirconia-10 mol% scandia is reported in this work. Cylindrical pellets were prepared by solid state synthesis with sintering at 1500 °C for 5 h. High relative density values (> 95%) were achieved. Reduction of the enthalpy for the cubic ⇌β-rhombohedral phase transformation was found for increasing amounts of the co-dopant. Full stabilization of the cubic structure at room temperature was obtained with only 0.45 mol% tantalum oxide addition. The ionic conductivity of sintered specimens was investigated as a function of the temperature and oxygen partial pressure by impedance spectroscopy. The fully stabilized co-doped system revealed a pure ionic conduction behavior up to 800 °C with wide electrolytic domain. In the 700–800 °C range, the ionic conductivity of co-doped specimens is similar to that of pure zirconia-scandia.

Porous ceria: 20 mol% gadolinia (20GDC) ceramic membranes were prepared by tape casting (TC) and freezedrying (FD) techniques, obtaining ceramic matrices with randomly dispersed round pores and with an aligned pore structure, respectively. Samples were sintered at 1450 degrees C, followed by infiltration of molten eutectic sodium-lithium carbonates (NLC). The pore morphology of 20GDC-TC and 20GDC-FD composite membranes was evaluated by analysis of scanning electron microscopy images. The electrical resistivity was determined by electrochemical impedance spectroscopy in the 1 Hz - 10 MHz frequency range from 300 degrees C to 700 degrees C, covering the solid-to-molten NLC temperature range, showing that the aligned pore structure improved the conductivity of the ceramic matrix in addition to facilitating molten carbonate infiltration, improving the total (bulk + interfaces) electrical conductivity of the composite membrane. Permeation experiments showed high CO2 permeation rates reached 5.35 x 10- 7 mol m- 2 s- 1 Pa-1 at 800 degrees C. The infiltration of molten sodium-lithium carbonate in gadolinium-doped ceria prepared by the freeze-drying technique is proposed as an optimized procedure for producing membranes for carbon dioxide separation.

Cosintering (La0.84Sr0.16MnO3 thin-film cathode/ZrO2: 8 mol% Y2O3 thin-film solid electrolyte/55 vol.% ZrO2:8 mol% Y2O3 + 45 vol.% NiO anode, phi = 12 x 1.5 mm thick pellet) was achieved by applying an electric field for 5 min at 1200 degrees C. Impedance spectroscopy measurements of the anode-supported three-layer cell show an improvement of the electrical conductivity in comparison to that of a conventionally sintered cell. The scanning electron microscopy images of the cross-sections of electric field-assisted pressureless sintered cells show a fairly dense electrolyte and porous anode and cathode. Joule heating, resulting from the electric current due to the application of the AC electric field, is suggested as responsible for sintering. Dilatometric shrinkage curves, electric voltage and current profiles, impedance spectroscopy diagrams, and scanning electron microscopy micrographs show how anode-electrolyte-cathode ceramic cells can be cosintered at temperatures lower than the usually required.

Gadolinium oxide ceramic powders were mixed to cerium oxide ceramic powders, pressed to pellets, and sintered either at 1450 degrees C or applying 200 V cm(-1) electric field at 800 degrees C, 900 degrees C and 1000 degrees C. The structural phases and the microstructure of the sintered pellets were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The formation of substitutional solid solution was followed by monitoring the increase of the electrical conductivity by impedance spectroscopy and X-ray diffraction. The main results show that Joule heating due to the flow through the pellets of the electric current, which was produced by the application of the electric field, allows for promoting partial solid solution as well as partial sintering the ceria-gadolinia pellets. Moreover, grain growth that occurred in the high temperature sintered pellets was inhibited in the electric field-assisted synthesized/sintered pellets, being an alternative technique for producing cerium oxide-gadolinium oxide solid solutions.

Green compacts of Li7La3Zr1.9Ta0.1O12 ceramic powders, synthesized by solid state reaction, were sintered by applying electric fields at 590 oC and 670 oC during 5 min. Thickness shrinkage, electric voltage and current were monitored simultaneously. The electrical resistivity of the sintered pellets was evaluated by the impedance spectroscopy technique. Even though Li7La3Zr1.9Ta0.1O12 solid electrolytes may be sintered at temperatures and times lower than those used in conventional sintering, X-ray diffraction analyses showed non-homogeneous distribution of structural phases, with cubic phase in the bulk and tetragonal phase at the pellet surfaces.

The properties of ZrO2: 8 mol% Y2O3 (8YSZ) ceramics with LiF and KCl sintering aids for liquid phase formation during electric field-assisted sintering were studied. Sintering experiments were carried out at 650 degrees C under 200 V cm(-1) AC electric field by varying current density, current application time, as well as LiF and KCl contents. Pellets sintered with KCl addition had cavities, cracks and fractures. Pellets sintered with 15 wt.% LiF, on the other hand, were homogeneous after thermal removal of LiF upon Joule heating. Low electric current densities coupled with longer application times produced homogeneous specimens. Three different stages were identified during sintering experiments: (i) LiF melting with the electric field applied at furnace temperatures lower than its melting point, (ii) shrinkage due to liquid phase formation and LiF removal, (iii) final densification due to grain growth and pore elimination. The electrical behavior and an estimate of the porosity were carried out by electrochemical impedance spectroscopy measurements.

Green compacts of Li7La3Zr1.9Ta0.1O12 ceramic powders, synthesized by solid state reaction, were sintered by applying electric fields at 590 oC and 670 oC during 5 min. Thickness shrinkage, electric voltage and current were monitored simultaneously. The electrical resistivity of the sintered pellets was evaluated by the impedance spectroscopy technique. Even though Li7La3Zr1.9Ta0.1O12 solid electrolytes may be sintered at temperatures and times lower than those used in conventional sintering, X-ray diffraction analyses showed non-homogeneous distribution of structural phases, with cubic phase in the bulk and tetragonal phase at the pellet surfaces.

Composite ceramic membranes were prepared according to two routes: (i) vacuum impregnation of molten eutectic sodium-lithium carbonates (NLC) into porous ceria-20 mol% gadolinia (20GDC) solid electrolytes; (ii) electric field-assisted sintering of a 25 wt% NLC/75 wt% 20GDC mixture. Porous 20GDC ceramics were obtained by controlled thermal removal of 40 vol% KCl added as pore former. Electric field-assisted (flash) sintering was carried out monitoring thickness during application of 200 V cm−1 to the specimen positioned in a sample chamber inserted in a vertical dilatometer. The surfaces of the sintered membranes were observed in a scanning electron microscope. Electrochemical impedance spectroscopy measurements were performed in the 5 Hz to 13 MHz frequency range in the 280–580°C range. Arrhenius plots showed the transition from oxide ion conduction (due to the solid electrolyte) to carbonate ion conduction (due to the molten NLC). Membranes flash sintered at 420°C in 2 min showed electrical conductivity similar to membranes conventionally sintered at 690°C for 2 h.