Person: Prado Gonjal, Jesús De La Paz
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First Name
Jesús De La Paz
Last Name
Prado Gonjal
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Inorgánica
Area
Química Inorgánica
Identifiers
7 results
Search Results
Now showing 1 - 7 of 7
Item In situ generation of 3D graphene-like networks from cellulose nanofibres in sintered ceramics(Nanoscale, 2018) Kocjan, Andraz; Schmidt, Rainer; Lazar, Ana; Prado-Gonjal, Jesus; Prado Gonjal, Jesús De La Paz; Kovac, Janez; Logar, Manca; Mompean, Francisco J; García-Hernández, Mar; Ruiz-Hitzky, Eduardo; Wicklein, BerndEstablishing a 3D electrically percolating network in an insulating matrix is key to numerous engineering and functional applications. To this end, using hydrophobic carbon nanofillers is tempting, but still results in suboptimal performance due to processing challenges. Here, we demonstrate how natural cellulose nanofibres can be in situ transformed into graphene-like sheets connected to a 3D network enhancing both the transport and the mechanical properties of sintered engineering ceramics. The network architecture also permits the decoupling of electrical and thermal conductivities, which represents a major obstacle in attaining efficient thermoelectric materials. We foresee that our transferable methodology can pave the way for the use of natural nanofibres to unravel the full potential of 3D graphene-like networks to accelerate development in fields like energy and telecommunications.Item Substantial thermal conductivity reduction in mischmetal skutterudites Mm_xCo_4Sb_12 prepared under high-pressure conditions, due to uneven distribution of the rare-earth elements(Journal of Materials Chemistry C, 2019) Gainza, Javier; Serrano Sánchez, F.; Prado Gonjal, Jesús De La Paz; Nemes, Norbert Marcel; Biskup Zaja, Nevenko; Dura, O.J.; Martínez, J.L.; Fauth, F.; Alonso, J.A.Thermoelectric mischmetal-filled Mm(x)Co(4)Sb(12) (Mm: natural cocktail of rare-earth elements, mostly Ce and La) skutterudites have been synthesized and sintered in one step under high-pressure conditions at 3.5 GPa in a piston-cylinder hydrostatic press. Synchrotron X-ray diffraction patterns display a splitting of the diffraction peaks ascribed to purely Ce-, and Mm-filled skutterudite phases, which have been analyzed and confirmed by high-resolution TEM and EELS. A total thermal conductivity () of 1.51 W m(-1) K-1 is measured at 773 K for Mm(0.5)Co(4)Sb(12), below that of other filled skutterudites, which is promoted by the enhanced phonon scattering over a broad range of the phonon spectrum due to the inhomogeneous and nanoscale mischmetal inclusion. Compared to undoped CoSb3 skutterudite synthesized by conventional methods, is reduced by a factor of 3, while the power factor is also substantially enhanced.Item Thermal conductivity reduction by fluctuation of the filling fraction in filled cobalt antimonide skutterudite thermoelectrics(ACS Applied Energy Materials, 2018) Serrano Sánchez, F.; Prado Gonjal, Jesús De La Paz; Nemes, Norbert Marcel; Biskup Zaja, Nevenko; Dura, O. J.; Martinez, J. L.; Fernandez Diaz, M. T.; Fauth, F.; Alonso, J. A.The reduction of the lattice thermal conductivity is one of the crucial steps in improving thermoelectric materials. In skutterudites, a well-known approach is to reduce the thermal conductivity by filling the structural cage with rare-earth atoms. In this work, we show that it is not just the amount of such filling itself but its nanoscale structuration that lowers the thermal conductivity. A straightforward synthesis procedure under high pressure yields Ce- and Yb-filled CoSb3 skutterudites, with and without an inhomogeneous distribution of the filler atoms. The composition of the phases is evaluated from synchrotron Xray diffraction (SXRD) data; the highly nanostructured morphology is verified by high-resolution transmission electron microscopy (TEM). The filling fluctuation, i.e., the uneven distribution of filling atoms in the sample originating a phase segregation, brings about low lattice thermal conductivity, as a strong source of phonon scattering. This effect is prominent in the Ce-filled compound, where Ce is segregated into Ce-rich and Ce-poor regions, and the lattice contribution of the thermal conductivity kappa(L), shows a concomitant reduction, approaching values as low as 1.6 W m(-1) K-1 at 800 K. Although the level of filling is much higher in YbxCoSb3, its lattice thermal conductivity remains larger. Overall, though, its power factor is enhanced due to charge transfer from the Yb-filler. We thus define a new paradigm for the design of filled skutterudites with exceptionally low thermal conductivities, based on the nanoscale mixing of two phases with different filling factors, spontaneously induced by high-pressure synthesis conditions, which can be considered as pseudoamorphous structures with significant reduction in kappa(L).Item Structural, magnetic and dielectric properties of the novel magnetic spinel compounds ZnCoSnO₄ and ZnCoTiO₄(Journal of the european ceramic society, 2018) Ruiz León, Domingo; Mompean, Federico; Prado Gonjal, Jesús De La Paz; Marco, José F.; García Hernandez, Mar; Schmid, RainerThe transparent semiconductor Zn₂SnO₄ with cubic spinel structure and the isostructural Zn₂Ti₄O have been magnetically doped with Co^(2++) ZnCoSnO₄ and ZnCoTiO₄ exhibit ferrimagnetism below TN ≈ 13 K and TN ≈ 17 K. Ferrimagnetic moments are evident in M vs H curves below TN by small hysteresis. Fits to strictly linear Curie-Weiss plots above TN give µ_(eff) ≈ to 4.86 µ(B) and a ≈ to 4.91 µB for ZnCoSnO₄ and ZnCoTiO₄, above theoretical predictions. Impedance spectroscopy data from sintered ceramic can be fitted with a standard equivalent circuit model based on two RC elements for bulk and GB areas. The relative dielectric permittivity of the bulk is ≈ 20 and ≈ to 30 for Zn₂SnO₄ and Zn₂TiO₄. The semiconducting ZnCoSn SnO₄ and ZnCoTiO₄ceramics exhibit bulk resistivity of ≈ to 1 10⁶Ω cm and ≈ to 1 10⁵ Ωcm at 560 K (287°C), and bulk activation energies of EA ≈ to 1.2 eV and 1.1 eV.Item Structural and dielectric properties of ultra-fast microwave-processed La_0.3Ca_0.7Fe_0.7Cr_0.3O3-delta ceramics(Journal of solid state chemistry, 2022) Sánchez Ahijón, Elena; Schmidt, Rainer; Martínez De Irujo Labalde, Xabier; Haris Masood, Ansari; Fernández Díaz, María Teresa; Morán, Emilio; Molero Sánchez, Beatriz; Prado Gonjal, Jesús De La PazPerovskite La_0.3Ca_0.7Fe_0.7Cr_0.3O_(3-delta) (LCFCr) is a mixed ionic and electronic conductor (MIEC) that can be employed as an electrode material in reversible solid oxide fuel cells (RSOFCs). In this work, an ultra-fast (15 min) one-step microwave (MW)-assisted combustion synthesis route has been developed to obtain phase pure and highly crystalline LCFCr powder. The synthesized powders exhibited a sponge-like microstructure with increased electrochemical reaction sites. Neutron thermodiffraction analysis revealed a structural transition above 500 degrees C from the room temperature (RT) orthorhombic Pnma to a rhombohedral R3c perovskite phase. The oxygen vacancy concentration was found to increase from delta = 0.272(7) at RT to delta = 0.333(5) at 900 degrees C. Furthermore, a 3-dimensional G-type antiferromagnetic structure was detected at RT. MW-sintering of pressed green ceramic pellets was carried out at 950 degrees C for 1 h, using a MW-transparent quartz fiber crucible or alternatively a SiC crucible acting as a MW-absorber. Impedance spectroscopy data on sintered ceramic pellets revealed electronic inhomogeneity as demonstrated by the occurrence of three dielectric relaxation processes associated with two grain boundary (GB)-like contributions and one bulk. The dielectric inhomogeneity encountered may be restricted to the extrinsic GB areas, which may be rather thin. More homogeneous dielectric properties of the GBs were found in the pellet that was sintered in the SiC crucible.Item From theory to experiment: BaFe0.125Co0.125Zr0.75O3-delta, a highly promising cathode for intermediate temperature SOFCs(Journal of Materials Chemistry A, 2020) Sánchez Ahijón, Elena; Marín Gamero, Rafael; Molero Sánchez, Beatriz; Ávila Brande, David; Manjón Sanz, Alicia; Fernández Díaz, M. Teresa; Morán, Emilio; Schmidt, Rainer; Prado Gonjal, Jesús De La PazIn a recent theoretical study [Jacobs et al., Adv. Energy Mater., 2018, 8, 1702708], BaFe0.125Co0.125Zr0.75O3-delta was predicted to be a stable phase with outstanding performance as an auspicious cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). It is shown here that the theoretical predictions are valid. The material can be synthesized by the citrate method as a single cubic Pm3m phase with a significant amount of oxygen vacancies, randomly distributed in the anionic sublattice facilitating oxygen vacancy conduction. A thermal expansion coefficient of 8.1 x 10(-6) K-1 suggests acceptable compatibility with common electrolytes. Electrochemical impedance spectroscopy of symmetrical cells gives an area-specific resistance of 0.33 Omega cm(2) at 700 degrees C and 0.13 Omega cm(2) at 800 degrees C. These values are reduced to 0.13 Omega cm(2) at 700 degrees C and 0.05 Omega cm(2) at 800 degrees C when the material is mixed with 30 wt% Ce0.9Gd0.1O2-delta.Item Effects of sintering temperature on the internal barrier layer capacitor (IBLC) structure in CaCu3Ti4O12 (CCTO) ceramics(Journal of the European Ceramic Society, 2012) Schmidt, Rainer; Stennett, Martin; Hyatt, Neil; Pokorny, Jan; Prado Gonjal, Jesús De La Paz; Ming Li; Sinclair, DerekThe formation of the internal barrier layer capacitor (IBLC) structure in CaCu3Ti4O12 (CCTO) ceramics was found to be facilitated by the ceramic heat treatment. Electrically insulating grain boundary (GB) and semi-conducting grain interior areas were characterized by impedance spectroscopy to monitor the evolution of the IBLC structure with increasing sintering temperature TS (975–1100 °C). The intrinsic bulk and GB permittivity increased by factors of ≈2 and 300, respectively and the bulk resistivity decreased by a factor of ≈103. These trends were accompanied by increased Cu segregation from the CCTO ceramics as detected by scanning electron microscopy and quantitative energy dispersive analysis of X-rays. The chemical changes due to possible Cu-loss in CCTO ceramics with increasing TS are small and beyond the detection limits of X-ray absorption spectroscopy near Cu and Ti K-edges and Raman Spectroscopy.