Optimum in the thermoelectric efficiency of nanostructured Nb-doped TiO<sub>2</sub>ceramics: from polarons to Nb–Nb dimers

Verchère, Alexandre; Pailhés, S.; Floch, Sylvie Le; Cottrino, Sandrine; Debord, Régis; Fantozzi, Gilbert; Misra, Shantanu; Candolfi, Christophe; Lenoir, Bertrand; Danièle, S.; Mishra, Shashank

doi:10.1039/d0cp00652a

Cited by 14 publications

(14 citation statements)

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“…While TN30 exhibits the highest power factor of 470 μW m –1 K –2 at room temperature, the ZT value was only 0.04 due to the relatively high thermal conductivity; nevertheless, this is still the highest ZT value at room temperature. At elevated temperatures, the ZT values increase with increasing Nb content, to a maximum value of 0.17 for TN60 at 873 K. The ZT values from this study are presented graphically alongside data from other studies ,,− , for single Nb-doped TiO 2 -based thermoelectric ceramics in Figure b. The present results show approximately 50% enhancement in ZT at 373 K compared with earlier studies.…”

Section: Resultssupporting

confidence: 63%

“…At elevated temperatures, the ZT values increase with increasing Nb content, to a maximum value of 0.17 for TN60 at 873 K. The ZT values from this study are presented graphically alongside data from other studies 1,12,[54][55][56]61 for single Nb-doped TiO 2 -based thermoelectric ceramics in Figure 11b. The present results show approximately 50% enhancement in ZT at 373 K compared with earlier studies.…”

Section: ■ Results and Discussionmentioning

confidence: 65%

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Controlling the Thermoelectric Properties of Nb-Doped TiO₂ Ceramics through Engineering Defect Structures

Liu

Kepaptsoglou

Gao

et al. 2021

ACS Appl. Mater. Interfaces

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Donor-doped TiO 2 ceramics are promising high-temperature oxide thermoelectrics. Highly dense (1 − x)TiO 2 −xNb 2 O 5 (0.005 ≤ x ≤ 0.06) ceramics were prepared by a single-step, mixed-oxide route under reducing conditions. The microstructures contained polygonal-shaped grains with uniform grain size distributions. Subgrain structures were formed in samples with low Nb contents by the interlacing of rutile and higher-order Magneĺi phases, reflecting the high density of shear planes and oxygen vacancies. Samples prepared with a higher Nb content showed no subgrain structures but high densities of planar defects and lower concentrations of oxygen vacancies. Through optimizing the concentration of point defects and line defects, the carrier concentration and electrical conductivity were enhanced, yielding a much improved power factor of 5.3 × 10 −4 W m −1 K −2 at 823 K; lattice thermal conductivity was significantly reduced by enhanced phonon scattering. A low, temperature-stable thermal conductivity of 2.6 W m −1 K −1 was achieved, leading to a ZT value of 0.17 at 873 K for compositions with x = 0.06, the highest ZT value reported for single Nb-doped TiO 2 ceramics without the use of spark plasma sintering (SPS). We demonstrate the control of the thermoelectric properties of Nbdoped TiO 2 ceramics through the development of balanced defect structures, which could guide the development of future oxide thermoelectric materials.

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Section: Resultssupporting

confidence: 63%

Section: ■ Results and Discussionmentioning

confidence: 65%

Controlling the Thermoelectric Properties of Nb-Doped TiO₂ Ceramics through Engineering Defect Structures

Liu

Kepaptsoglou

Gao

et al. 2021

ACS Appl. Mater. Interfaces

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“…The EXAFS results also indicate that it is unlikely that Nb forms dimers as has been postulated in some Nb-doped TiO 2 . 33 In other studies, anatase thin films were prepared from a composite TiNb target by reactive magnetron sputtering giving a level of 1.5% Nb doped in TiO 2 anatase. 29 The authors conclude that “the local environment of Nb atoms in the film is close to that of Ti atoms in the anatase phase [...].…”

Section: Resultsmentioning

confidence: 99%

Niobium K-Edge X-ray Absorption Spectroscopy of Doped TiO₂ Produced from Ilmenite Digested in Hydrochloric Acid

et al. 2022

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Niobium doping of TiO 2 creates a conductive material with many new energy applications. When TiO 2 is precipitated from HCl solutions containing minor Nb, the Nb in solution is quantitatively deposited with the TiO 2 . Here, we investigate the structure of Nb doped in anatase and rutile produced from ilmenite digested in hydrochloric acid. Nb K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) are used to characterize the environment of 0.08 atom % Nb doped in TiO 2 . XANES shows clear structural differences between Nb-doped anatase and rutile. EXAFS for Nb demonstrates that Nb occupies a Ti site in TiO 2 with no near neighbors of Nb. Hydrolysis of Ti and Nb from acid solution, followed by calcination, leads to a well dispersed doped material, with no segregation of Nb. Production of Nb-doped TiO 2 by this method may be able to supply future demand for large quantities of the material and in energy applications where a low cost of production, from readily available natural resources, would be highly desirable.

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“…A good TE efficiency requires materials with low thermal conductivity and high electrical conductivity. While a small amount of Nb (2-4 at.%) increases the electrical conductivity of TiO 2 by several orders of magnitude, it has been recently shown that the thermal conductivity of bulk nano-structured Nb-TiO 2 obtained by spark plasma sintering (SPS) is significantly lowered by decreasing the average grain size [1]. A value of 2.5 W/mK has been observed at 900 K for an average grain size of 170 nm, while the value in the single crystal is of about 4 W/mK.…”

Section: Introductionmentioning

confidence: 99%

Effect of High Pressure Spark Plasma Sintering on the Densification of a Nb-Doped TiO2 Nanopowder

et al. 2020

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Sintering under pressure by means of the spark plasma sintering (SPS) technique is a common route to reduce the sintering temperature and to achieve ceramics with a fine-grained microstructure. In this work, high-density bulk TiO2 was sintered by high pressure SPS. It is shown that by applying high pressure during the SPS process (76 to 400 MPa), densification and phase transition start at lower temperature and are accelerated. Thus, it is possible to dissociate the two densification steps (anatase then rutile) and the transition phase during the sintering cycle. Regardless of the applied pressure, grain growth occurs during the final stage of the sintering process. However, twinning of the grains induced by the phase transition is enhanced under high pressure resulting in a reduction in the crystallite size.

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Optimum in the thermoelectric efficiency of nanostructured Nb-doped TiO₂ceramics: from polarons to Nb–Nb dimers

Abstract: Thermoelectric properties of bulk nanostructured Nb-doped rutile TiO2.

Cited by 14 publications

References 81 publications

Controlling the Thermoelectric Properties of Nb-Doped TiO₂ Ceramics through Engineering Defect Structures

Controlling the Thermoelectric Properties of Nb-Doped TiO₂ Ceramics through Engineering Defect Structures

Niobium K-Edge X-ray Absorption Spectroscopy of Doped TiO₂ Produced from Ilmenite Digested in Hydrochloric Acid

Effect of High Pressure Spark Plasma Sintering on the Densification of a Nb-Doped TiO2 Nanopowder

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Optimum in the thermoelectric efficiency of nanostructured Nb-doped TiO2ceramics: from polarons to Nb–Nb dimers

Abstract: Thermoelectric properties of bulk nanostructured Nb-doped rutile TiO2.

Cited by 14 publications

References 81 publications

Controlling the Thermoelectric Properties of Nb-Doped TiO2 Ceramics through Engineering Defect Structures

Controlling the Thermoelectric Properties of Nb-Doped TiO2 Ceramics through Engineering Defect Structures

Niobium K-Edge X-ray Absorption Spectroscopy of Doped TiO2 Produced from Ilmenite Digested in Hydrochloric Acid

Effect of High Pressure Spark Plasma Sintering on the Densification of a Nb-Doped TiO2 Nanopowder

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Optimum in the thermoelectric efficiency of nanostructured Nb-doped TiO₂ceramics: from polarons to Nb–Nb dimers

Controlling the Thermoelectric Properties of Nb-Doped TiO₂ Ceramics through Engineering Defect Structures

Controlling the Thermoelectric Properties of Nb-Doped TiO₂ Ceramics through Engineering Defect Structures

Niobium K-Edge X-ray Absorption Spectroscopy of Doped TiO₂ Produced from Ilmenite Digested in Hydrochloric Acid