TKato AMomma SNagata and YKasuga Electrotechnical Laboratory 114 Umezono Tsukuba Ibaraki Japan

Introduction

The stress induced in Solid oxide fuel cells (SOFC)s has important influence on the lifetime of SOFC. But the data on stress in SOFC and mechanical properties of SOFC component materials have not been accumulated enough to manufacture SOFC. Especially, the data of La^Sr^MnO, cathode and La, jS^CrOj interconnection have been extremely limited. We have estimated numerically the dependences of residual stress in SOFC on the material properties, the cell structure and the fabrication temperatures of the components m, but these unknown factors have caused obstruction to simulate the accurate behavior of residual stress. Therefore, the residual stresses in deposited Lal xSrxMn03 and La^SrCrO., films are researched by the observation of the bending behavior of the substrate strips. The films of SOFC component materials were prepared by the RF sputtering method, because: (1) It can fabricate dense films of poor sintcrable material such as La^Sr^CrO, compared with sintering or plasma spray method. (2) For the complicated material such as perovskite materials, the difference between the composition of a film and that of a target material is generally small. (3) It can fabricate a thick ceramics film by improving of the deposition rate. For example, A1203 thick films of 50pm can be fabricated with the deposition rate of approximately 5pm/h industrially. In this paper, the dependence of residual stress on the deposition conditions is defined and mechanical properties of these materials are estimated from the results of the experiments.

Experimental

The sputtering conditions to fabricate the films are listed in

Table 1. The thickness of each deposited film was approximately lfim . La09Sr01MnO3 and La0 85Sr0IJCrO3

powders were used for the sputtering target. A1203, the mixture of A120, and MgO (SP) whose weight ratio of Mg0/Al203

was 1, and MgO were adopted as the substrates. The surfaces of the substrate strips were polished up to mirror finished and their dimensions were 1mm thick, 10mm wide and 50mm long. Their material properties are shown in Table 2. The crystal structure of the film was determined by X-ray diffractometer (XRD). The composition of the film was measured by energy-dispersive X-ray spectrometer (EDX) and induced coupled plasma spectrometer (ICP). The deflection S at the center of substrate induced by the deposited film was measured by the Fizeau interferometer. A typical example of the change of its image by the deposition is shown in Fig. 1. The residual stress of the film a was estimated by the following equation(2).

Tablel. Sputtering conditions

RF Power /W

0 0

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