Pyrochlore type semiconducting ceramic oxides in Ca–Ce–Ti–M–O system (M=Nb or Ta)—Structure, microstructure and electrical properties

Deepa, M.; Rao, P. Prabhakar; Radhakrishnan, A. N.; Sibi, K.S.; Koshy, Peter

doi:10.1016/j.materresbull.2009.02.014

Cited by 38 publications

(12 citation statements)

References 33 publications

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“…Pyrochlore structured composition have a wide range of technically important properties such as high ionic conductivity, superconductivity, luminescence and ferromagnetism [5]. Lanthanide based pyrochlore are emerging as an important class of solid oxide materials with potential applications as ionic conductors [6], thermal barrier coatings [7], nuclear waste storage materials [8], scintillators and semiconductors [9]. These applications are due to the structural flexibility of pyrochlores and specifically mobility of anions [10].…”

Section: Introductionmentioning

confidence: 99%

Environmentally sustainable facile synthesis of nanocrystalline holmium hafnate (Ho2Hf2O7): Promising new oxide-ion conducting solid electrolyte

et al. 2020

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A 2 B 2 O 7 oxides with defect-fluorite structure are one of the potential candidates for solid oxide fuel cell electrolyte material due to their excessive thermodynamic stability in oxygen potential gradient at elevated temperature between 500 and 900 °C. Holmium hafnate nanoparticles have been synthesised through the Leeds Alginate Process (LAP) using inorganic salts of holmium and hafnium as starting materials immobilized in alginate beads. Ion exchange with sodium alginate and its subsequent thermal treatment have been used to prepare the nanopowder of Ho 2 Hf 2 O 7 . Thermal decomposition of dried beads is carried out at 700 °C for 2 h and 6 h to obtain the nanoparticles of Ho 2 Hf 2 O 7 . This calcination temperature was determined after carrying out simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/ DSC). High Temperature X-ray Diffraction (HT-XRD) was carried out to gain further insight into the thermal decomposition process in static ambient environment. HT-XRD analysis corroborated with the results obtained from TGA/DSC. Nanocrystalline powder of single phase Ho 2 Hf 2 O 7 has been obtained by calcination of oven dried ion-exchanged alginate beads in relatively low temperature range of 500-700 °C. Rietveld refinement of X-ray diffraction (XRD) data confirmed the formation of single phase defect fluorite structure of Ho 2 Hf 2 O 7 . The crystallographic parameters calculated from TEM and XRD analysis are in excellent agreement with each other. Furthermore, TEM-EDX analysis confirms that the Ho 2 Hf 2 O 7 synthesised by the facile alginate process is nearly stoichiometric. Raman spectroscopy gives evidence of the presence of oxide-ion vacancy in holmium hafnate which is supported with ac-impedance spectroscopy measurement at selected three temperatures. The present study suggests that the LAP has the capability of yielding on a large scale single phase defect-fluorite nanoparticles of electrolyte materials for solid oxide fuel cells in environmentally sustainable, economical and energy efficiently manner.

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Section: Introductionmentioning

confidence: 99%

Environmentally sustainable facile synthesis of nanocrystalline holmium hafnate (Ho2Hf2O7): Promising new oxide-ion conducting solid electrolyte

et al. 2020

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“…C omplex oxides have yielded numerous materials of interest to solid‐state chemists, condensed matter physicists, and materials scientists. They exhibit interesting transport properties such as superconductivity, 1 metallic conductivity, 2 semiconductivity, 3 magnetism, etc. Semiconducting oxides are a very important group of materials; their applications span through photocatalysts, 4 negative temperature coefficient (NTC) thermistors, 5 gas sensors, 6 etc.…”

Section: Introductionmentioning

confidence: 99%

New Negative Temperature Coefficient Ceramics in Ca–Ce–Nb–M–O (M=Mo or W) System

Deepa

Rao

Sumi

et al. 2010

Journal of the American Ceramic Society

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A series of quaternary powellites with varying cerium contents in a Ca–Ce–Nb–M–O (where M=Mo or W) system has been synthesized through the solid‐state route. Powder X‐ray diffraction analysis shows that these compounds crystallize in a tetragonal powellite structure with the I41/a space group. The structure was further confirmed by Raman spectroscopic analysis. The electrical conductivity studies reveal that they exhibit negative temperature coefficient (NTC) thermistor characteristics. The characteristic parameter of the thermistor (β) is found to be in the range of 5000–7000 K, and these values can be tuned with the cerium concentration. The electrical conductivity in these compounds is due to the presence of Ce3+, which remains in the reduced state without being oxidized to Ce4+ due to the structural stabilization. The X‐ray photoelectron spectroscopy analysis corroborates the presence of Ce in the 3+ state.

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“…Pyrochlore oxides have attracted considerable attention in many areas of Material Science during the last few decades, due to their chemical and structural flexibility as well as their wide range of properties, such as superconductivity [1,2], semi-conductivity [3], ionic conductivity [4,5], ferromagnetism [6] and luminescence [7,8]. Oxide ion-conducting pyrochlores find applications in solid oxide fuel cells as electrolytes [9,10] and gas sensors.…”

Section: Introductionmentioning

confidence: 99%

Structural, electrical and magnetic properties of the pyrochlorate Er_2-x Sr_x Ru_2O_7 (0<=x<=0.10) system

Abatal

2018

Rev. Mex. Fís.

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In this research, we report a detailed study of the structural, electrial and magnetic properties of the ruthenium pyrochlore with the composition (Er_2-x Sr_x) Ru_2O_7 0<=x<=0.10 prepared by solid-state reaction in air at ambient pressure. The synthesized products were characterized using powder X-ray diffraction. The structure of the samples was refined with the Rietveld method, showing that the lattice parameters are more sensitive to the Strontium and Erbium sites. Scanning electron microscopy shows that the crystal size varies between 0.27 and 0.62 mu m. In all polycrystalline samples, the electrical resistance decreases with increasing temperature, indicating that the samples are nonmetallic. The slope of the temperature-dependent resistance profiles systematically decreases with increasing x, proving that the carrier concentration increases with increasing the Sr content. Zero-field-cooled and field cooled magnetization measurements show an irreversible behavior where the split is systematically enhanced by increasing x.

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Pyrochlore type semiconducting ceramic oxides in Ca–Ce–Ti–M–O system (M=Nb or Ta)—Structure, microstructure and electrical properties

Cited by 38 publications

References 33 publications

Environmentally sustainable facile synthesis of nanocrystalline holmium hafnate (Ho2Hf2O7): Promising new oxide-ion conducting solid electrolyte

Environmentally sustainable facile synthesis of nanocrystalline holmium hafnate (Ho2Hf2O7): Promising new oxide-ion conducting solid electrolyte

New Negative Temperature Coefficient Ceramics in Ca–Ce–Nb–M–O (M=Mo or W) System

Structural, electrical and magnetic properties of the pyrochlorate Er_2-x Sr_x Ru_2O_7 (0<=x<=0.10) system

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