Fabrication of Non-Stoichiometric Titanium Dioxide by Spark Plasma Sintering and Its Thermoelectric Properties

Lu, Yun; Sagara, Katsuhiro; Hao, Liang; Ji, Ziwu; Yoshida, Hiroyuki

doi:10.2320/matertrans.e-m2012808

Cited by 19 publications

(7 citation statements)

References 23 publications

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“…Many physical and chemical properties are often strong functions of δ including, for example, electrical conductivity, magnetic permeability, optical absorptivity and luminescence, oxygen and cation diffusivities, and thermal conductivity . As an illustrative example, the room temperature electrical conductivity of TiO 2‐δ can differ by many orders of magnitude as δ varies from near zero to ∼ 0.01 …”

Section: Introductionmentioning

confidence: 99%

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Chen

Tuller

2014

Adv Funct Materials

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While the properties of functional oxide thin films often depend strongly on oxygen stoichiometry, there have been few means available for its control in a reliable and in situ fashion. This work describes the use of DC bias as a means of systematically controlling the stoichiometry of oxide thin films deposited onto yttria‐stabilized zirconia substrates. Impedance spectroscopy is performed on the electrochemical cell Pr0.1Ce0.9O2−δ (PCO)/YSZ/Ag for conditions: T = 550 to 700 °C, pO 2 = 10−4 to 1 atm, and ΔE = ‐100 to 100 mV. The DC bias ΔE is used to control the effective pO 2 or oxygen activity at the PCO/YSZ interface. The non‐stoichiometry (δ) of the PCO films is calculated from the measured chemical capacitance (Cchem ). These δ values, when plotted isothermally as a function of effective pO 2, established, either by the surrounding gas composition alone, or in combination with applied bias, agree well with each other and to predictions based on a previously determined defect model. These results confirm the suitability of using bias to precisely control δ of thin films in an in situ fashion and simultaneously monitor these changes by measurement of Cchem . Of further interest is the ability to reach effective pO 2s as high as 280 atm.

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Section: Introductionmentioning

confidence: 99%

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Chen

Tuller

2014

Adv Funct Materials

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“…As high-temperature generation is the main application prospect for TiO 2 as a thermolectric material, it is crucial to accurately predict the transport properties between 300 K and 2000 K. In Ref. 20, the electrical conductivity and Seebeck coefficients of reduced rutile samples, subjected to spark plasma sintering (SPS) at different temperatures, have been measured up to 523 K. The conductivity displays a very weak temperature dependance, even though the scattering rate, equation ( 5), increases substantially with elevated temperature. This suggests an activation mechanism for the electron density in the conduction band, as confirmed by the Hall measurements in Ref.…”

Section: High-temperature Thermoelectric Performancesmentioning

confidence: 99%

“…Of these, rutile is particularly stable at high temperatures with a melting point around 2100 K, while anatase and brookite undergo a phase transition to rutile near 1000 K. Additionally, the carrier concentration of rutile can be tuned by doping with several elements such as boron, niobium or cobalt, or by using reduction processes to introduce oxygen vacancies acting as electron donors. [17][18][19][20] Therefore, this compound would represent a very promising prospect for waste heat recovery applications if its thermoelectric properties could be optimized. 21 In this paper, we investigate the electron transport properties of n-type rutile TiO 2 by combining first-principle calculations with a modelling of electronphonon interactions and donor defects.…”

Section: Introductionmentioning

confidence: 99%

Investigating the high-temperature thermoelectric properties of n -type rutile TiO2

2019

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Transition metal oxides are considered promising thermoelectric materials for harvesting hightemperature waste heat due to their chemical and thermal stability, abundance and low toxicity. Despite their typically strong ionic character, they can exhibit surprisingly high power factors σS 2 , as in n-type SrTiO3 for instance. Thus, it is worth examining other transition metal oxides that might equal or even surpass the performances of strontium titanate. This theoretical paper investigates the thermoelectric properties of n-type rutile TiO2, which is the most stable phase of titanium oxide up to 2000 K. The electronic structure is obtained through density functional theory calculations, while the prominent features of strong electron-phonon interaction and defects states are modelled using a small number of parameters. The thermoelectric transport properties are computed by solving the Boltzmann transport equation with the relaxation time approximation. The theoretical results are compared with a wealth of experimental data from the literature, yielding very good agreements over a wide range of carrier concentrations. This validates the hypothesis of band conduction in rutile TiO2 and allows the prediction of the high-temperature thermoelectric properties. arXiv:1909.08554v2 [cond-mat.mtrl-sci]

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“…10,11) It suggests the combination of SPS and the following reduction treatment is effective and feasible to improve the thermoelectric performance of TiO 2 . For the unpolished sample ( Fig.…”

Section: Thermoelectric Propertiesmentioning

confidence: 99%

“…The measurement method of thermoelectric properties has been described and can be found in our early work 11) and it will not be involved here. The Seebeck coefficient and electrical resistivity were measured by the static method and 4-probe method respectively in air from room temperature up to 573 K. In that temperature range, the re-oxidation effect on the thermoelectric properties was rather weak and can be neglected.…”

Section: Measurements Of Thermoelectric Propertiesmentioning

confidence: 99%

Improvement in Thermoelectric Properties of Non-Stoichiometric Titanium Dioxide by Reduction Treatment

Hao

Sagara

et al. 2013

Mater. Trans.

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Compacts of non-stoichiometric TiO 2¹x were fabricated by SPS and the following reduction treatment in carbon powder. XRD, SEM and EPMA were used to characterize the compacts. The results showed that they were composed of non-stoichiometric TiO 2¹x inside and TiO as the surface layer. The thickness of the surface layer was increased with the increase of the holding time and exceeded 100 µm when it came to 20 h. Carbon did not penetrate into the compacts during the reduction treatment. To examine the carrier density and the non-stoichiometric number, 2 ¹ x, thermogravimetry was carried out. The study showed that the value of 2 ¹ x was decreased and the carrier density was increased as the holding time increased. The thermoelectric properties including electrical resistivity, Seebeck coefficient and power factor was measured. The electric resistivity was considerably reduced by the reduction treatment. The values of the Seebeck coefficient was also decreased by the reduction treatment but maintained at a large absolute value of 250 µV·K ¹1 at 573 K. Power factor reached 2 © 10 ¹4 W·m ¹1 ·K ¹2 at 573 K. The value was much higher than that of the samples by SPS only. Therefore, the thermoelectric performance was improved by the reduction treatment. The influence of the TiO layer on the thermoelectric performance was also examined. It was believed that the influence should result from its comprehensive effect on Seebeck coefficient and electrical resistivity.

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Fabrication of Non-Stoichiometric Titanium Dioxide by Spark Plasma Sintering and Its Thermoelectric Properties

Cited by 19 publications

References 23 publications

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Investigating the high-temperature thermoelectric properties of n -type rutile TiO2

Improvement in Thermoelectric Properties of Non-Stoichiometric Titanium Dioxide by Reduction Treatment

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Fabrication of Non-Stoichiometric Titanium Dioxide by Spark Plasma Sintering and Its Thermoelectric Properties

Cited by 19 publications

References 23 publications

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr0.1Ce0.9O2−δ Case Study

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr0.1Ce0.9O2−δ Case Study

Investigating the high-temperature thermoelectric properties of n -type rutile TiO2

Improvement in Thermoelectric Properties of Non-Stoichiometric Titanium Dioxide by Reduction Treatment

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Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr_0.1Ce_0.9O_2−δ Case Study