Mixed ionic-electronic conductivity and thermochemical expansion of Ca and Mo co-substituted pyrochlore-type Gd2Ti2O7

Zakharchuk, Kiryl; Kravchenko, Ekaterina; Fagg, Duncan P.; Frade, J.R.; Yaremchenko, A.A.

doi:10.1039/c6ra14600g

Cited by 13 publications

(4 citation statements)

References 46 publications

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“…: Li-ion battery 8,9 , photoluminescence 10,11 , laser materials 12 , solid oxide fuel cells 13,14 …). They possess exotic physical properties 15–18 exuding a strong interest in their modelling and simulation 19,20 .…”

Section: Introductionmentioning

confidence: 99%

Fingerprint of local disorder in long range ordered isometric pyrochlores

Martel

Naji

Popa

et al. 2017

Sci Rep

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The detailed characterization of local order and disorder in isometric A2B2O7 crystalline pyrochlores is of significant importance in view of their wide range and sensitive technological applications. Nevertheless, much remains to be understood concerning their atomic scale structures. Here we specifically pinpoint local order and disorder in four stoichiometric Ln2Zr2O7 (Ln = La, Nd, Sm and Eu) pyrochlores using a combination of three standard easily available laboratory techniques: XRD, 17O solid-state MAS NMR and Raman spectroscopy. The evolution of the oxygen sub-lattice identifies specific features (extra 17O NMR signals and Raman bands) which undoubtedly reveal local oxygen order and disorder in these stoichiometric long range ordered crystalline pyrochlores. These results complete the understanding of the atomic scale in these stoichiometric pyrochlores necessitating the need for new microscopic structural models.

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Section: Introductionmentioning

confidence: 99%

Fingerprint of local disorder in long range ordered isometric pyrochlores

Martel

Naji

Popa

et al. 2017

Sci Rep

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“…A similar increase in activation energy was reported for donor-doped pyrochlore type oxides such as Nb and Mo-doped Gd 2 Ti 2 O 7 . , The lower activation energy in the low-temperature regime, where oxygen stoichiometry might be fixed, may be attributed to activated electron or hole hopping between Mn neighbors and/or ionic conductivity (see Discussion below).…”

Section: Resultsmentioning

confidence: 99%

Stabilizing Coexisting n-Type Electronic and Oxide Ion Conductivities in Donor-Doped Ba–In-Based Oxides under Oxidizing Conditions: Roles of Oxygen Disorder and Electronic Structure

et al. 2019

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Surface oxygen reduction reaction (ORR) rates at n-type oxide-based mixed ionic–electronic conducting (MIEC) solid oxide fuel cell (SOFC) cathodes can be expected to be enhanced relative to that at p-type MIEC cathodes due to the greater availability of electrons at higher energies in the band structure needed for the charge transfer reaction. However, given the difficulty of achieving coexisting oxygen vacancies and electrons in the conduction band under oxidizing cathode conditions, no stable n-type MIEC cathodes have been reported to date. In this study, a predominantly n-type MIEC conductivity is confirmed in a Ba–In-based oxide (BNIM) co-doped with Nd and Mn at high temperature and high P O2 confirmed by the P O2 dependence of the electrical conductivity and negative Seebeck coefficients, combined with readily measurable oxide ion transference numbers. This coexistence of n-type electronic and oxide ion conductivities is discussed based on the electrical behavior of BNIM with different Mn levels and is attributed to the significant change in the degree of anion Frenkel ordering and the band structure associated with heavy donor doping of Ba2In2O5. This novel n-type MIEC has the potential for enhancing the ORR at SOFC cathodes at reduced temperatures and thereby identifying new potential candidate cathode materials for next-generation SOFCs.

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“…This enhancement is attributed to the in uence of disordering in oxygen vacancies on the activation energy associated with the oxygen hopping dynamics and long-range oxygen diffusion, along with the structural deformation induced by aliovalent dopant. [26][27]30] Thus, GTO systems show signi cant potential for optimization as oxygenion conductors for low-temperature SOFCs, by inducing structural deformation and disordering of oxygen vacancies through non-stoichiometric aliovalent doping strategies [31].…”

Section: Introductionmentioning

confidence: 99%

Understanding of charge relaxation dynamics of Sr doped on Gd 2 Ti 2 O 7 pyrochlore system as Electrolyte for IT-SOFCs

Ali,

Acharya,

Bhongale

et al. 2024

Preprint

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The pyrochlore-based system is gaining significant attention as a solid electrolyte in electrochemical energy devices, particularly solid oxide fuel cells (SOFC) due to its high oxygen-ion conductivity at the Intermediate temperature range (400−650 o C). In this study, we investigate the Gd 2 − x Sr x Ti 2 O 7 , pyrochlore system doped with strontium (Sr), where, x = 0, 0.02 and 0.04, 0.06, 0.08 and 0.1 to develop an oxygen-ion conductor as an electrolyte for intermediate temperature SOFCs (IT-SOFCs). Structural information is collected using the X-ray diffraction technique and confirms the cubic pyrochlore phase with Fd−3m symmetry accompanied by superstructure peaks (111) (311) (511) and (111) planes across all compositions. The structural data are simulated using Rietveld Refinement. Microstructural features of as-calcined and sintered samples studied by Scanning Electron Microscopy; confirm non-spherical grains with high non-uniformity in particle size distribution. of as-calcined samples and highly dense sintered samples. Elemental composition is confirmed by EDAS. Raman spectroscopy reveals detailed insights into the dopant-induced local restructuring in the Gadolinium Titanate lattice. Few intense Raman modes related to Eg+F2g and Alg involve the modulation of crystal structure through the vibration of oxygen along < 100 > cubic axis. Ionic conductivity and activation energy data are extracted through AC impedance measurements. The electric modulus study reveals the ionic relaxation and ion hopping dynamics and their effect on ionic conductivity. M'' relaxation peak and its distribution in relaxation time are analyzed using the Kohlrausch-Williams-Watts (KWW) fit. The presence of dopants induced structural deformations and oxygen vacancies in the GTO host lattice. This led to the disordering of vacancies and modifications in the stretching exponent 'β' and activation energy. Cooperative hopping dynamics through ion-vacancy interactions are found to be a notable influence on ionic conductivity. The optimized dopant composition of GSTO−4 exhibits the highest conductivity peak (σ = 4.3 x 10 − 3 S/cm@650oC). This suggests that apart from vacancy concentration and energy barriers for single-ion hopping, the cooperative dynamics of oxygen ions play a crucial role in determining the ionic conductivity values. Consequently, the GSTO−4 system demonstrates the potential for application as an electrolyte in intermediate temperature-SOFCs.

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Mixed ionic-electronic conductivity and thermochemical expansion of Ca and Mo co-substituted pyrochlore-type Gd₂Ti₂O₇

Abstract: Co-substitutions with calcium and molybdenum in pyrochlore-type (Gd1−xCax)2(Ti1−yMoy)2O7−δ induce mixed ionic-electronic conductivity under reducing conditions characteristic for solid oxide fuel cell anode operation.

Cited by 13 publications

References 46 publications

Fingerprint of local disorder in long range ordered isometric pyrochlores

Fingerprint of local disorder in long range ordered isometric pyrochlores

Stabilizing Coexisting n-Type Electronic and Oxide Ion Conductivities in Donor-Doped Ba–In-Based Oxides under Oxidizing Conditions: Roles of Oxygen Disorder and Electronic Structure

Understanding of charge relaxation dynamics of Sr doped on Gd 2 Ti 2 O 7 pyrochlore system as Electrolyte for IT-SOFCs

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