Preparation of Oxygen Ion Conducting Doped Lanthanum Gallate Thin Films on Amorphous and Single Crystal Substrates by Pu
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Preparation of Oxygen Ion Conducting Doped Lanthanum Gallate Thin Films on Amorphous and Single Crystal Substrates by Pulsed Laser Deposition Fumiaki Mitsugi, Seiji Kanazawa1, Toshikazu Ohkubo1, Yukiharu Nomoto1, Yusaku Takita2 and Tatsumi Ishihara3 Venture Business Laboratory, Oita University, 700 Dannoharu, Oita 870-1192, Japan 1 Department of Electrical and Electronic Engineering, Oita University, 700 Dannoharu, Oita 870-1192, Japan 2 Department of Applied Chemistry, Oita University, 700 Dannoharu, Oita 870-1192, Japan 3 Department of Applied Chemistry, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan ABSTRACT An La1-xSrxGa1-y-zMgyCozO3-(x+y+z)/2 (LSGMCO) has attracted much attention because it can be useable as an electrolyte of a solid oxide fuel cell due to its high oxide ion conductivity. We prepared LSGMCO thin films on silica glass and LaAlO3 single crystal substrates by pulsed laser deposition and evaluated their properties. LSGMCO thin films deposited at 800oC were poly-crystal and the deposition pressure affected their surface morphologies. In the case of the LaAlO3 single crystal substrate, a c-axis oriented LSGMCO thin film was obtained. DC conductivity and complex impedance of LSGMCO thin films were measured in vacuum atmosphere to investigate the effect of the crystal orientation on the oxide ion conductivity. It was revealed that resistance at a grain boundary of films is more dominant compare with the grain interior. INTRODUCTION A doped LaGaO3 such as La1-xSrxGa1-yMgyO3-(x+y)/2 (LSGMO) has one order magnitude higher oxide ion conductivity than yttria stabilized zirconia (YSZ) [1,2]. A unit cell of the LSGMO has a structure of ABO3 perovskite and the ion radius of the B (Ga, Mg) site, which exists at the center of the BO3 octahedron, affects the oxide ion conductivity. In particular, Co is an effective transition metal in increasing oxide ion conductivity. An La1-xSrxGa1-y-zMgyCozO3-(x+y+z)/2 (LSGMCO) is one of promising candidates for electrolytes of solid oxide fuel cells (SOFCs) or oxygen gas sensors [3-5]. However, a large amount of the Co addition to the B site of the LSGMO causes a decrease of the oxide ion transport number. Then, we employ the LSGMCO with the composition of La0.8Sr0.2Ga0.8Mg0.15Co0.05O2.8. There are many reports on properties for bulk materials of LSGMO or LSGMCO and on attempts to apply them to electrolytes of SOFCs and gas sensor [6-8]. Recently, thin film fabrication techniques for the YSZ, LSGMO and LSGMCO have been investigated in order to reduce an operating temperature of SOFCs [9,10]. However, it is difficult to make thin films with correct composition especially for the LSGMCO. We have evaluated properties of LSGMCO thin films fabricated by pulsed laser deposition [11] and also have tried to deposit LSGMCO thin film electrolytes onto porous anodes of SOFCs [12]. In this work, we deposited LSGMCO thin films on silica glass and LaAlO3 single crystal substrates by pulsed laser deposition. Structural, crystal and electrical properties for LSGMCO thin
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