Structure Refinement of (Sr,Ba)Nb2O6 Ceramic Powder from Neutron and X-Rays Diffraction Data

Carrió, J. G.; Mascarenhas, Yvonne P.; Yelon, W. B.; Santos, I. A.; Garcia, D.; Eiras, J. A.

doi:10.1590/s1516-14392002000100010

Cited by 27 publications

(23 citation statements)

References 11 publications

(19 reference statements)

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“…After an A‐site occupancy of 1 is reached, any additional decrease in the oxygen activity is accommodated by an additional phase. More accurate determination of the site occupancies could be achieved via Rietveld refinements as has been done previously for air‐fired SBN, but unlike previous studies, the A‐site vacancy concentration must be refined in the current work. This additional degree of freedom renders refinements of the system unconstrained if only XRD and compositional analysis are used.…”

Section: Resultssupporting

confidence: 82%

“…The formula unit can be represented as (A1) 2 (A2) 4 C 4 B 10 O 30 where both the A1 and A2 sites host strontium ions, barium ions sit exclusively on the A2 site, the C‐site is empty, and Nb fills the B‐sites inside the oxygen octahedra. Only five‐sixth of the A1 and A2 sites are filled, resulting in an A‐site vacancy solid solution which is thought to contribute to the relaxor ferroelectric properties of SBN . Other tetragonal tungsten bronze materials show different cation site occupancies including, for example, in the ‘stuffed’ bronzes like K 6 Li 4 Nb 10 O 30 where all of the A1, A2, and C‐sites are completely filled, and the “filled” bronzes like Ba 4 Na 2 Nb 10 O 30 where the A1 and A2 sites are filled but the C‐sites remain empty .…”

Section: Introductionmentioning

confidence: 99%

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The Effects of Low Oxygen Activity Conditions on the Phase Equilibria and Cation Occupancy of Strontium Barium Niobate

et al. 2016

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Strontium barium niobate (SBN) is a tungsten bronze family ferroelectric which shows promising thermoelectric properties under reducing conditions. It is found here that the enhanced electrical conductivity of oxygen‐deficient SBN correlates with the formation of a NbO2 secondary phase. The effects of the reducing environment and the NbO2 phase formation are studied via a detailed defect chemistry analysis. Increasing amounts of the NbO2 phase are accompanied by an interesting mechanism where the A‐site occupancy of the SBN matrix increases. The resulting donor defects source the large carrier concentrations which cause the enhanced electrical conductivity necessary for thermoelectric performance. In investigation of the phase equilibria, it is found that a solid solution between (Sr0.6,Ba0.4)Nb2O6 and (Sr0.6,Ba0.4)1.2Nb2O6 exists and that the A‐site filling is found to occur at more modest reduction conditions in Sr‐ and Ba‐rich compositions. Finally, thermogravimetric analysis of the reoxidation process is performed, and the results suggest that the A‐site filling is compensated ionically. Not only do the presented results explain the enhanced electrical conductivity of oxygen‐deficient strontium barium niobate but also modification of the site occupancies by reduction and reoxidation may widen the design space for property modification in tungsten bronze‐structured materials in general.

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Section: Resultssupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

The Effects of Low Oxygen Activity Conditions on the Phase Equilibria and Cation Occupancy of Strontium Barium Niobate

et al. 2016

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“…[19][20][21] The process is simple but requires a high temperature. Thus, the particle sizes of the synthesized powders tend to be large and nonuniform.…”

Section: Introductionmentioning

confidence: 99%

A novel sol–gel route to synthesize (Sr0.5Ba0.5)Nb₂O₆ ceramics with enhanced electrocaloric effect

Chen

Liu

et al. 2017

J. Adv. Dielect.

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(Sr 0:5 Ba 0:5 )Nb 2 O 6 ultra-fine powders were synthesized by a novel sol-gel route, and the mechanism of the reaction was discussed. SrCO 3 , BaCO 3 , oxalate niobium and citric acid were used to initiate the sol-gel process, and ethylene glycol (EG) was added to further polymerize the cross-linking structure. The evolution of the (Sr 0:5 Ba 0:5 )Nb 2 O 6 phase, the reaction process and the microstructures were investigated by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy, DSC-TG and scanning electron microscopy. The synthesis temperature of the (Sr 0:5 Ba 0:5 )Nb 2 O 6 powders reached as low as 1200 C, and the size and morphology of the powders were controlled by temperature. By adjusting the calcination temperature, we obtained (Sr 0:5 Ba 0:5 )Nb 2 O 6 powders with uniform sizes of 20 nm to 500 nm. Then, dense (Sr 0:5 Ba 0:5 )Nb 2 O 6 ceramics were successfully prepared using these ultrafine powders. Finally, an enhanced electrocaloric effect (ECE) value of 0.35 C was obtained at 100 kV/cm.

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“…x 0.75), T c may vary from 325 (x = 0.25) to 470 K (x = 0.75). 23 Many different approaches have been employed to fabricate SBN powders, including solid-state processing, [24][25][26] sol-gel-based synthesis, [27][28][29] and aqueous organic gel routes. [30][31][32] However, these methods have a few disadvantages.…”

Section: Introductionmentioning

confidence: 99%

Thermoelectric Properties of Reduced Polycrystalline Sr_0.5Ba_0.5Nb₂O₆ Fabricated Via Solution Combustion Synthesis

et al. 2013

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The thermoelectric properties of bulk polycrystalline Sr0.5Ba0.5Nb2O6 (SBN50) fabricated via solution combustion synthesis (SCS) and reduced at temperatures of 900°C–1150°C were explored. The Seebeck coefficient (S) of all samples increased over the entire range of testing temperatures; a peak S value of −281 μV/K was obtained at 930 K for the sample reduced at 900°C. A metal‐insulator transition was observed in the electrical conductivity (σ) of samples reduced at 1000°C–1150°C, whereas only semiconducting electrical behavior was observed for the sample reduced at 900°C. An optimal balance between S and σ was achieved for the pellet reduced at 1000°C, which exhibited a maximum power factor of 1.78 μW/cm·K2 at 930 K. Over a temperature range of 300–930 K, the thermal conductivity (κ) of as‐processed and reduced (1000°C) SBN50 was found to be 1.03–1.4 and 1.46–1.84 W/m·K, respectively. A maximum figure of merit (ZT) of 0.09 was obtained at 930 K for the 1000°C‐reduced sample. X‐ray photoelectron spectroscopy revealed that the Nb2+ peak intensity increased at higher reduction temperatures, which could possibly lead to a distortion of NbO6 octahedra and a decrease in the Seebeck coefficient.

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Structure Refinement of (Sr,Ba)Nb2O6 Ceramic Powder from Neutron and X-Rays Diffraction Data

Cited by 27 publications

References 11 publications

The Effects of Low Oxygen Activity Conditions on the Phase Equilibria and Cation Occupancy of Strontium Barium Niobate

The Effects of Low Oxygen Activity Conditions on the Phase Equilibria and Cation Occupancy of Strontium Barium Niobate

A novel sol–gel route to synthesize (Sr0.5Ba0.5)Nb₂O₆ ceramics with enhanced electrocaloric effect

Thermoelectric Properties of Reduced Polycrystalline Sr_0.5Ba_0.5Nb₂O₆ Fabricated Via Solution Combustion Synthesis

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Structure Refinement of (Sr,Ba)Nb2O6 Ceramic Powder from Neutron and X-Rays Diffraction Data

Cited by 27 publications

References 11 publications

The Effects of Low Oxygen Activity Conditions on the Phase Equilibria and Cation Occupancy of Strontium Barium Niobate

The Effects of Low Oxygen Activity Conditions on the Phase Equilibria and Cation Occupancy of Strontium Barium Niobate

A novel sol–gel route to synthesize (Sr0.5Ba0.5)Nb2O6 ceramics with enhanced electrocaloric effect

Thermoelectric Properties of Reduced Polycrystalline Sr0.5Ba0.5Nb2O6 Fabricated Via Solution Combustion Synthesis

Contact Info

Product

Resources

About

A novel sol–gel route to synthesize (Sr0.5Ba0.5)Nb₂O₆ ceramics with enhanced electrocaloric effect

Thermoelectric Properties of Reduced Polycrystalline Sr_0.5Ba_0.5Nb₂O₆ Fabricated Via Solution Combustion Synthesis