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Title: Photo- and gas-tuned, reversible thermoelectric properties and anomalous photo-thermoelectric effects of platinum-loaded tungsten trioxide

Abstract

We report the photo- and gas-controllable properties of platinum-loaded tungsten trioxide (Pt/WO{sub 3}), which is of interest for developing practical applications of WO{sub 3} as well as for interpreting such phenomena from scientific viewpoints. Here, a Pt/WO{sub 3} thin film generated a thermoelectric power due to the ultraviolet-light-induced band-gap excitation (photochromic (PC) reaction) and/or dark storage in formic acid vapor (gaschromic (GC) reaction) in the absence of O{sub 2}, resulting from the generation of W{sup 5+} ions. After such chromic reactions, the electrical conductivity (σ) is increased, whereas the absolute value of the Seebeck coefficient (S) is decreased. The changes in σ and S and their rate of change for consistency increased in the order of: during the PC reaction < during the GC reaction < during simultaneous PC and GC reactions. The opposite behaviors, a decrease in σ and an increase in S, were exhibited by Pt/WO{sub 3} in the presence of O{sub 2} after dark storage or visible-light irradiation. This reversible cycle could be repeated. Moreover, anomalous, nontrivial photo-thermoelectric effects (a photoconductive effect (photoconductivity, σ{sub photo}) and a photo-Seebeck effect (photo-Seebeck coefficient, S{sub photo})) were also detected in response to the visible-light irradiation of Pt/WO{sub 3} in themore » absence of O{sub 2} after chromic reactions. Under visible-light irradiation, both σ{sub photo} and the absolute value of S{sub photo} are increased. After the irradiation, both values were decreased, that is, σ and the absolute value of S were smaller than σ{sub photo} and the absolute value of S{sub photo}, respectively. These effects are likely to be due to the photoinduced charge carriers and the accumulated electrons in Pt contributing to the increase in σ{sub photo}. In addition, electrons are extracted from the W{sup 5+} state, decreasing the number of W{sup 5+} in H{sub x}WO{sub 3} and thus contributing to the increase in S{sub photo}. After light irradiation, the accumulated electrons in Pt are returned to the energetically favorable W{sup 5+} state, and Pt/H{sub x}WO{sub 3} are returned to the initial state. Then both σ and S are decreased. The mechanisms of our anomalous, nontrivial photo-thermoelectric effects are presumed to be different from that involving the two-carrier contribution to the transport properties.« less

Authors:
;  [1]; ;  [2]
  1. Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi 400-8511 (Japan)
  2. Clean Energy Research Center, University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi 400-8511 (Japan)
Publication Date:
OSTI Identifier:
22596675
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 119; Journal Issue: 24; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CHARGE CARRIERS; ELECTRONS; EXCITATION; FORMIC ACID; IRRADIATION; PHOTOCONDUCTIVITY; PLATINUM; SEEBECK EFFECT; THERMOELECTRIC PROPERTIES; THIN FILMS; TRANSPORT THEORY; TUNGSTATES; TUNGSTEN IONS; TUNGSTEN OXIDES; ULTRAVIOLET RADIATION

Citation Formats

Suzuki, Kenta, Watanabe, Takuya, Kakemoto, Hirofumi, and Irie, Hiroshi, E-mail: hirie@yamanashi.ac.jp. Photo- and gas-tuned, reversible thermoelectric properties and anomalous photo-thermoelectric effects of platinum-loaded tungsten trioxide. United States: N. p., 2016. Web. doi:10.1063/1.4954874.
Suzuki, Kenta, Watanabe, Takuya, Kakemoto, Hirofumi, & Irie, Hiroshi, E-mail: hirie@yamanashi.ac.jp. Photo- and gas-tuned, reversible thermoelectric properties and anomalous photo-thermoelectric effects of platinum-loaded tungsten trioxide. United States. doi:10.1063/1.4954874.
Suzuki, Kenta, Watanabe, Takuya, Kakemoto, Hirofumi, and Irie, Hiroshi, E-mail: hirie@yamanashi.ac.jp. Tue . "Photo- and gas-tuned, reversible thermoelectric properties and anomalous photo-thermoelectric effects of platinum-loaded tungsten trioxide". United States. doi:10.1063/1.4954874.
@article{osti_22596675,
title = {Photo- and gas-tuned, reversible thermoelectric properties and anomalous photo-thermoelectric effects of platinum-loaded tungsten trioxide},
author = {Suzuki, Kenta and Watanabe, Takuya and Kakemoto, Hirofumi and Irie, Hiroshi, E-mail: hirie@yamanashi.ac.jp},
abstractNote = {We report the photo- and gas-controllable properties of platinum-loaded tungsten trioxide (Pt/WO{sub 3}), which is of interest for developing practical applications of WO{sub 3} as well as for interpreting such phenomena from scientific viewpoints. Here, a Pt/WO{sub 3} thin film generated a thermoelectric power due to the ultraviolet-light-induced band-gap excitation (photochromic (PC) reaction) and/or dark storage in formic acid vapor (gaschromic (GC) reaction) in the absence of O{sub 2}, resulting from the generation of W{sup 5+} ions. After such chromic reactions, the electrical conductivity (σ) is increased, whereas the absolute value of the Seebeck coefficient (S) is decreased. The changes in σ and S and their rate of change for consistency increased in the order of: during the PC reaction < during the GC reaction < during simultaneous PC and GC reactions. The opposite behaviors, a decrease in σ and an increase in S, were exhibited by Pt/WO{sub 3} in the presence of O{sub 2} after dark storage or visible-light irradiation. This reversible cycle could be repeated. Moreover, anomalous, nontrivial photo-thermoelectric effects (a photoconductive effect (photoconductivity, σ{sub photo}) and a photo-Seebeck effect (photo-Seebeck coefficient, S{sub photo})) were also detected in response to the visible-light irradiation of Pt/WO{sub 3} in the absence of O{sub 2} after chromic reactions. Under visible-light irradiation, both σ{sub photo} and the absolute value of S{sub photo} are increased. After the irradiation, both values were decreased, that is, σ and the absolute value of S were smaller than σ{sub photo} and the absolute value of S{sub photo}, respectively. These effects are likely to be due to the photoinduced charge carriers and the accumulated electrons in Pt contributing to the increase in σ{sub photo}. In addition, electrons are extracted from the W{sup 5+} state, decreasing the number of W{sup 5+} in H{sub x}WO{sub 3} and thus contributing to the increase in S{sub photo}. After light irradiation, the accumulated electrons in Pt are returned to the energetically favorable W{sup 5+} state, and Pt/H{sub x}WO{sub 3} are returned to the initial state. Then both σ and S are decreased. The mechanisms of our anomalous, nontrivial photo-thermoelectric effects are presumed to be different from that involving the two-carrier contribution to the transport properties.},
doi = {10.1063/1.4954874},
journal = {Journal of Applied Physics},
number = 24,
volume = 119,
place = {United States},
year = {Tue Jun 28 00:00:00 EDT 2016},
month = {Tue Jun 28 00:00:00 EDT 2016}
}
  • The addition of photo-controllable properties to tungsten trioxide (WO{sub 3}) is of interest for developing practical applications of WO{sub 3} as well as for interpreting such phenomena from scientific viewpoints. Here, a sputtered crystalline WO{sub 3} thin film generated thermoelectric power due to ultraviolet (UV) light-induced band-gap excitation and was accompanied by a photochromic reaction resulting from generating W{sup 5+} ions. The thermoelectric properties (electrical conductivity (σ) and Seebeck coefficient (S)) and coloration of WO{sub 3} could be reversibly switched by alternating the external stimulus between UV light irradiation and dark storage. After irradiating the film with UV light, σmore » increased, whereas the absolute value of S decreased, and the photochromic (coloration) reaction was detected. Notably, the opposite behavior was exhibited by WO{sub 3} after dark storage, and this reversible cycle could be repeated at least three times. Moreover, photo-thermoelectric effects (photo-conductive effect (photo-conductivity, σ{sub photo}) and photo-Seebeck effect (photo-Seebeck coefficient, S{sub photo})) were also detected in response to visible-light irradiation of the colored WO{sub 3} thin films. Under visible-light irradiation, σ{sub photo} and the absolute value of S{sub photo} increased and decreased, respectively. These effects are likely attributable to the excitation of electrons from the mid-gap visible light absorption band (W{sup 5+} state) to the conduction band of WO{sub 3}. Our findings demonstrate that the simultaneous, reversible switching of multiple properties of WO{sub 3} thin film is achieved by the application of an external stimulus and that this material exhibits photo-thermoelectric effects when irradiated with visible-light.« less
  • A hexagonal form of WO{sub 3} (a = 7.3244(6), c = 7.6628(5) {angstrom}, z = 6) was synthesized by the low temperature sintering of an ammonium peroxo-polytungstate precursor. This compound, the N/W ratio of which is 0.015 at most, is not identical to reported hexagonal WO{sub 3} from WO{sub 3}{center dot}1/3 H{sub 2}O because its c-axis is significantly shorter than that of the latter (7.798 {angstrom}). Powder XRD profile refinements were performed in the space group P6{sub 3}/mcm. The authors found two kinds of structural models that showed reasonably good profile agreement (R {approx} 0.07). Both models are built upmore » of remarkably distorted WO{sub 6} octahedra, in which part of the O-O distances are very short (2.32 {approximately} 2.42 {angstrom}). Electrochemical intercalation of lithium into the present WO{sub 3} framework work was investigated using a Li{vert bar}LiPF{sub 6}{vert bar}WO{sub 3} cell. It was found that Li was intercalated reversibly up to the composition Li{sub 1.0}WO{sub 3}.« less
  • The anodic oxidation of tungsten in nitrate melts and the electrochromic properties of the resulting oxide layers were studied. Optimum conditions for the formation of WO/sub 3/ oxide films having satisfactory electrochromic characteristics were established. Anodic oxide layers on tungsten were shown to have high stability in sulfuric acid solutions, and guarantee at least 10/sup 6/ color changes.
  • Fine-grained Ti-doped FeVSb half-Heusler alloys were synthesized by combining mechanical alloying and spark plasma sintering and their thermoelectric properties were investigated with an emphasis on the influences of Ti doping and phase purity. It was found that substituting V with Ti can change the electrical transport behavior from n-type to p-type due to one less valence electron of Ti than V, and the sample with nominal composition FeV{sub 0.8}Ti{sub 0.4}Sb exhibits the largest Seebeck coefficient and the maximum power factor. By optimizing the sintering temperature and applying annealing treatment, the power factor is significantly improved and the thermal conductivity ismore » reduced simultaneously, resulting in a ZT value of 0.43 at 500 Degree-Sign C, which is relatively high as for p-type half-Heusler alloys containing earth-abundant elements. - Graphical abstract: Fine-grained Ti-doped FeVSb alloys were prepared by the MA-SPS method. The maximum ZT value reaches 0.43 at 500 Degree-Sign C, which is relatively high for p-type half-Heusler alloys. Highlights: Black-Right-Pointing-Pointer Ti-doped FeVSb half-Heusler alloys were synthesized by combining MA and SPS. Black-Right-Pointing-Pointer Substituting V with Ti changes the electrical behavior from n-type to p-type. Black-Right-Pointing-Pointer Thermoelectric properties are improved by optimizing sintering temperature. Black-Right-Pointing-Pointer Thermoelectric properties are further improved by applying annealing treatment. Black-Right-Pointing-Pointer A high ZT value of 0.43 is obtained at 500 Degree-Sign C for p-type Ti-doped FeVSb alloys.« less
  • In this paper we describe an experimental setup designed to measure simultaneously and very accurately the resistivity and the absolute thermoelectric power, also called absolute thermopower or absolute Seebeck coefficient, of solid and liquid conductors/semiconductors over a wide range of temperatures (room temperature to 1600 K in present work). A careful analysis of the existing experimental data allowed us to extend the absolute thermoelectric power scale of platinum to the range 0-1800 K with two new polynomial expressions. The experimental device is controlled by a LabView program. A detailed description of the accurate dynamic measurement methodology is given in thismore » paper. We measure the absolute thermoelectric power and the electrical resistivity and deduce with a good accuracy the thermal conductivity using the relations between the three electronic transport coefficients, going beyond the classical Wiedemann-Franz law. We use this experimental setup and methodology to give new very accurate results for pure copper, platinum, and nickel especially at very high temperatures. But resistivity and absolute thermopower measurement can be more than an objective in itself. Resistivity characterizes the bulk of a material while absolute thermoelectric power characterizes the material at the point where the electrical contact is established with a couple of metallic elements (forming a thermocouple). In a forthcoming paper we will show that the measurement of resistivity and absolute thermoelectric power characterizes advantageously the (change of) phase, probably as well as DSC (if not better), since the change of phases can be easily followed during several hours/days at constant temperature.« less