Investigations on electrical conduction properties and crystallization conditions of V 2 O 5 -P 2 O 5 glass based semico

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Investigations on electrical conduction properties and crystallization conditions of V2O5-P2O5 glass based semiconductors Akifumi Matsuda1, Takuya Aoyagi2, Takashi Naito1,2, Tadashi Fujieda2, Kenjiro Ikejiri3, Koji Koyama3, Ryosuke Yamauchi1, Geng Tan1, Satoru Kaneko1,4, and Mamoru Yoshimoto1 1 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259-J3-16 Nagatsuta, Midori, Yokohama 226-8502, Japan. 2 Hitachi Research Laboratory, Hitachi Ltd., 7-1-1 Omika, Hitachi 319-1292, Japan. 3 Namiki Precision Jewel Co., Ltd., 3-8-22 Shinden, Adachi, Tokyo 123-8511, Japan. 4 Kanagawa Industrial Technology Center, 705-1 Shimoimaizumi, Ebina 243-0435, Japan. ABSTRACT We studied the electrical properties of thermally treated V2O5-CuO-Fe2O3-P2O5 (vanadate) glasses under reducing high-vacuum conditions. The glasses were prepared by using a melt-quenching method and then applied on Al2O3 substrates as ~40μm-thick films. The glass films were then heat treated at 375í550°C under a vacuum of 10í6 Pa. Powder X-ray diffraction showed the formation of complex oxides of both MxV2O5 (M = Cu, Fe; x = 0.12í1.3) and vanadium oxides (VOx; x = 1.5í2.5). The resistivity of the glass film crystallized at 550°C measured at 50°C and 300°C were 1.8 × 100 Ωcm and 2.8 × 10í1 Ωcm, respectively, which was 10 times lower than that of the film crystallized in air. The Seebeck coefficient was í132 μV/K at 50°C and í130 μV/K at 300°C. These results show that the vanadate glasses crystallized under the appropriate condition become potential candidate materials for semiconductor and thermoelectric application. INTRODUCTION Thermoelectric (TE) generation has been recognized as a promising energy-harvesting technology because it provides a direct conversion of thermal energy [1]. Chalcogenide compounds such as Bi2Te3- and PbTe-related materials with relatively high figure-of-merit (ZT > 1) have been used at temperatures up to 800°C [2]. However, the major drawbacks of TE devices based on these substances are the consistently low thermal-to-electric conversion efficiency of ~8% (when compared to that of photovoltaic generation) and the toxic and rare elements in their composition. Thus, the search for alternative nontoxic and environmentally friendly TE materials as well as improved conversion characteristics is important. Nonetheless, there have been reports of alternative TE materials such as layered cobalt oxides and heavily doped SrTiO3 [3], and some organic materials [4], e.g., poly(3,4-ethylenedioxythiophene);polystyrene sulfonate (PEDOTPSS) [5]. On the other hand, vanadate glasses have semiconductor properties such as electric conductivity of about 105 Ωí1cmí1 due to the hopping conduction between V4+ and V5+ ions [68]. V2O5-P2O5 glasses are considered to have a layered structure comprising VO4, VO5, and PO4 polyhedra; moreover, they have a potential for applications in energy devices such as Li-ion batteries as well as Li1+xV1íxO2 layered compounds [9]. Few studies have been conducted regarding the thermoelectric applicabili

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