Modified Glycine Nitrate Procedure Research Articles

Development of a new system of solid ionic conductors based on multi-doped ceria for application in IT-SOFCs

Nanosized multi-doped ceria with composition Ce0.8Nd0.0025Sm0.0025Gd0.005Dy0.095Y0.095O2-? (CNSGDY) as perspective solid ionic conductor was obtained by modified glycine-nitrate procedure (MGNP) and room temperature self-propagating reaction (SPRT). The pressed pellets of both powders were sintered at 1550?C for 2 h in an air atmosphere. The obtained sintered samples were characterized by XRPD, Raman spectroscopy, FESEM, EDS and EIS methods. Despite a high temperature of sintering, XRPD and FESEM analyses of the samples confirmed appropriate dimensions of grains with fluorite structure. Overall concentration of introduced dopants (x = 0.2) in the structure of CeO2 after the sintering process was confirmed by EDS analysis. After sintering, Raman spectroscopy confirmed retention of the oxygen vacancies in the ceria lattice, which is in accordance with the improvement of ionic conductivity of solid ionic conductors. The highest value of total conductivity was obtained for the sintered MGNP sample at 700?C (4.22 ? 10?2 S cm?1), with the corresponding activation energy of 0.26 eV.

Geopolymer/CeO2 as Solid Electrolyte for IT-SOFC

As a material for application in the life sciences, a new composite material, geopolymer/CeO2 (GP_CeO2), was synthesized as a potential low-cost solid electrolyte for application in solid oxide fuel cells operating in intermediate temperature (IT-SOFC). The new materials were obtained from alkali-activated metakaolin (calcined clay) in the presence of CeO2 powders (x = 10%). Besides the commercial CeO2 powder, as a source of ceria, two differently synthesized CeO2 powders also were used: CeO2 synthesized by modified glycine nitrate procedure (MGNP) and self-propagating reaction at room temperature (SPRT). The structural, morphological, and electrical properties of pure and GP_CeO2-type samples were investigated by X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR), BET, differential thermal and thermogravimetric analysis (DTA/TGA), scanning electron microscopy (FE-SEM), energy dispersive spectrometer (EDS), and method complex impedance (EIS). XRPD and matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) analysis confirmed the formation of solid phase CeO2. The BET, DTA/TGA, FE-SEM, and EDS results indicated that particles of CeO2 were stabile interconnected and form a continuous conductive path, which was confirmed by the EIS method. The highest conductivity of 1.86 × 10−2 Ω−1 cm−1 was obtained for the sample GP_CeO2_MGNP at 700 °C. The corresponding value of activation energy for conductivity was 0.26 eV in the temperature range 500–700 °C.

Structural, morphological, and electrical properties of doped ceria as a solid electrolyte for intermediate-temperature solid oxide fuel cells

The solid solutions of CeO2 with one or more rare-earth oxides among Yb2O3, Sm2O3, and Gd2O3 are synthesized by either modified glycine nitrate procedure (MGNP) or self-propagating reaction at room temperature (SPRT). The overall mole fraction of rare-earth oxide dopants was x = 0.2. The characterization was committed by XRPD, TEM, BET, and Raman Spectroscopy methods. According to XRPD and Raman spectroscopy, the obtained products presented the single-phase solid solutions with basic fluorite-type CeO2 structure, regardless on the number and the concentration of dopants. Both XRPD and TEM analysis evidenced the nanometer particle dimensions. The defect model was applied to calculate lattice parameters of single-, co-, and multi-doped solids. The sintering of the sample nanopowders was performed at 1550 °C, in air atmosphere. The sintered samples were characterized by XRPD, SEM, and complex impedance methods. The sintering did not affect the concentration ratios of the constituents. The highest conductivity at 700 °C amounting to 2.14 × 10−2 and 1.92 × 10−2 Ω−1 cm−1 was measured for the sample Ce0.8Sm0.08Gd0.12O2−δ, synthesized by SPRT and MGNP methods, respectively. The corresponding activation energies of conductivity, measured in the temperature range 500–700 °C, amounted to 0.24 and 0.23 eV.

Structural study of nanosized yttrium-doped CaMnO3 perovskites

Nanostructured compounds with general formula Ca1–x Y x MnO3 (0 ≤ x ≤ 1) were synthesized by modified glycine nitrate procedure. In the next step, we have investigated crystal structure and microstructure of the synthesized samples using X-ray methods and Rietveld analysis. Focus of this research was the structural stability of the yttrium-doped CaMnO3 perovskite phases, which crystallize in orthorhombic space group Pnma. We observed that the unit cell volumes of the investigated compounds increase proportionally with yttrium amount. Furthermore, we investigated the influence of yttrium amount on Mn–O bond angles and distances, tilting of MnO6 octahedra and deformation due to the presence of Jahn–Teller distortion around Mn3+ cation. In order to estimate effective coordination of A and B sites, bond valence calculations (BVC) were performed for A and B site cations. Finally, the photoelectron spectroscopy (XPS) method was applied in order to follow yttrium concentration in the perovskite phases.

Electrical properties of multidoped ceria

Multidoped nanosized ceria powders were prepared by either modified glycine nitrate procedure (MGNP) or self-propagating reaction at room temperature (SPRT). As the dopants to CeO2, trivalent rare earth oxides such as Nd2O3, Sm2O3, Gd2O3, Dy2O3 and Y2O3 were used, with the total molar fraction of 20%. The pressed powder pellets were subjected to the densification by sintering at 1500°C, in an air atmosphere. A single-phase crystalline form was evidenced by X-ray diffractometry for both sintered materials. By means of complex impedance measurements, the conductivity of the sintered samples was determined as a function of temperature. At 700°C, the conductivity amounted to 2.19×10−2 and 1.40×10−2Ω−1cm−1 for the SPRT and for the MGNP sample, respectively. The corresponding values of activation energies of conductivity amounted to 0.72 (MGNP) and 0.59 (SPRT)eV in the temperature range 550–700°C.

Investigation of the structure and the magnetic behavior of nanostructure Ca1−xGdxMnO3 (x=0.05; 0.1; 0.15; 0.2) obtained by modified glycine nitrate procedure

The synthesis, crystal structure and magnetic properties of Ca1−xGdxMnO3 (x=0.05; 0.1; 0.15; 0.2) perovskite has been investigated. Powders with nominal compositions Ca0.95Gd0.05MnO3, Ca0.9Gd0.1MnO3, Ca0.85Gd0.15MnO3 and Ca0.8Gd0.2MnO3 were prepared using a modified glycine nitrate procedure. Obtained powders were calcinated in the temperature interval from 850°C to 950°C for 10min. All samples where characterized by DTA, XRD and SQUID magnetometry. The possibility of incorporation of Gd ions in the positions A of the perovskite structure was investigated by X-ray methods. Influence of Gd on unit cell volume of the perovskite compounds, occupation numbers and distances between atoms were analyzed by Rietveld refinement. Microstructure size–strain analysis was performed, as well. The results revealed that Gd entered positions A in the structure. Magnetic measurements showed that a Gd3+ substituted Ca2+ ions changes antiferromagnetic properties of CaMnO3 by introduction of ferromagnetic interaction due to a double exchange between Mn3+ and Mn4+ ions.

Electrical characterization of multidoped ceria ceramics

Ceria ceramics was obtained from multi-doped nanosized ceria powders prepared by both modified glycine nitrate procedure (MGNP) and self-propagating reaction at room temperature (SPRT). Rare earth elements such as Nd, Sm, Gd, Dy, Y, Yb were used as dopants. The overall mole fraction of dopants was 0.2. One-hour long sintering of powder compacts was performed at 1500°C in oxygen atmosphere. Phase composition, microstructure and ionic conductivity of sintered samples were analysed. Single-phase ceria was detected in all samples. In general, the increase in the number of dopants improved the ionic conductivity. The samples doped simultaneously with five dopants had the highest ionic conductivity, as evidenced by the impedance measurements. At 450°C, the conductivity of sample obtained by MGNP was 3.94×10−3Ω−1cm−1 whereas the conductivity of sample obtained by SPRT was 2.61×10−3Ω−1cm−1. The conductivity activation energy for MGNP and SPRT samples was measured to be 0.348 and 0.385eV, respectively. Finally, the conductivity decreased as the number of dopants increased to six.

Nanometric solid solutions of the fluorite and perovskite type crystal structures: Synthesis and properties

In this paper a short review of our results on the synthesis of nanosized CeO2, CaMnO3 and BaCeO3 solid solutions are presented. The nanopowders were prepared by two innovative methods: self propagating room temperature synthesis (SPRT) and modified glycine/nitrate procedure (MGNP). Different types of solid solutions with rare earth dopants in concentrations ranging from 0-0.25 mol% were synthesized. The reactions forming solid solutions were studied. In addition, the characteristics of prepared nanopowders, phenomena during sintering and the properties of sintered samples are discussed.

Synthesis, structural and magnetic properties of nanostructured Ca0.9Gd0.1MnO3 obtained by modified glycine nitrate procedure (MGNP)

Ca0.9Gd0.1MnO3 nanopowders with perovskite type crystal structure were synthesized by modified glycine nitrate procedure. Nanopowders were prepared by combining glycine with metal nitrates and/or metal acetates in their appropriate stoichiometric ratios. Modification of the procedure was performed by partial replacement of nitrates by acetates, in order to control the burn-up reaction. Obtained Ca0.9Gd0.1MnO3 powders were calcinated in the temperature interval from 850°C to 950°C for 10min. Properties such as phase evolution, lattice parameters, chemical composition and magnetic properties were monitored by DTA, X-ray diffraction, SEM/EDS and magnetic measurements. Magnetic measurements performed at the sample with the smallest crystallite size showed that a 10% of Gd3+ substituted Ca2+ ions changes antiferromagnetic properties of CaMnO3 by the introduction of ferromagnetic interaction due to a double exchange between Mn3+ and Mn4+ ions. Presence of competing interactions and their randomness lead to a formation of a spin glass state below Neel temperature TN=110K. From the high temperature magnetic susceptibility measurements effective magnetic moment of manganese ions is determined which lies between the values for Mn3+ and Mn4+ ions.

Preparation, sintering and electrical properties of nano-grained multidoped ceria

Multiply doped ceria nanopowders were synthesized by applying MGNP (modified glycine/nitrate procedure). The overall concentration of dopants was kept constant (x=0.2) whereby Gd ion as the main dopant was gradually substituted by Sm and by Sm+Y. The compositions of solid solutions were calculated by applying defect model introducing anion vacancy radius. Characterization of powders involved BET, TEM, XRD and chemical analyses. Densification was performed at 1500°C, in an oxygen atmosphere for 1h. The results showed that with increasing number of dopants, specific surface area of powders increased, followed by decrease of crystallite and grain sizes. Densification degree was also found to rise with increasing number of dopants. According to impedance measurements it was found that ionic conductivity was the highest 1.14×10−3Scm−1 at 450°C in sample doped with Gd, Sm and Y simultaneously.

The effect of Y2O3 addition on thermal shock behavior of magnesium aluminate spinel

The effect of yttria additive on the thermal shock behavior of magnesium aluminate spinel has been investigated. As a starting material we used spinel (MgAl2O4) obtained by the modified glycine nitrate procedure (MGNP). Sintered products were characterized in terms of phase analysis, densities, thermal shock, monitoring the damaged surface area in the refractory specimen during thermal shock and ultrasonic determination of the Dynamic Young modulus of elasticity. It was found that a new phase between yttria and alumina is formed, which improved thermal shock properties of the spinel refractories. Also densification of samples is enhanced by yttria addition.

Cerium oxide based nanometric powders: synthesis and characterization

Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate procedure. Solid solutions of the host compound CeO2 with one or more dopants in the lattice were synthesized. Rare earth cations (Re=Yb, Gd and Sm) were added to ceria in total concentration of x= 0.2 that was kept constant. The criterion in doping was to keep the value of lattice parameter of ceria unchanged. The lattice parameters were calculated by using the model that takes into account the existence of oxygen vacancies in the structure.

Modified glycine nitrate procedure (MGNP) for the synthesis of SOFC nanopowders

Nanopowders with perovskite type crystal structure were synthesized by modified glycine nitrate procedure. Modification of the procedure was performed by partial replacement of nitrates by acetates, in order to control the burn-up reaction. The obtained nanopowders, according to XRD results are single phase, independent of number of dopants. The yield of powder in all cases was very close to the theoretical one. Many different powders with perovskite type crystal structure were produced, with cation dopants on A as well as on B sites or both. Properties of the synthesized powders together with sintering tests are discussed.

Lattice Parameters of Gd-Doped Ceria Electrolytes

This paper deals with Gd-doped ceria solid solutions: Ce1−XGdXO2−d with "x" ranging from 0 to 0.2. Four different powders were synthesized by modified glycine nitrate procedure with very precise stoichiometry according to tailored composition. The method was modified by decreasing glycine/nitrate ratio to 0.5. All obtained solid solutions exhibit a fluorite-type crystal structure with composition dependent lattice parameters. The variation of the lattice parameter was studied and correlated with the equation describing the ion-packing model. It has been found that the change of lattice parameter versus Gd concentration obeys Vegard's rule very well. Results also show that all powders are nanometric in size. The average size of Ce1−XGdXO2−d particles is about 20 nm.