Time-Dependent Degradation Due to the Gradual Phase Change in BICUVOX and BICOVOX Oxide-Ion Conductors at Temperatures below about 500°C
✍ Scribed by Akiteru Watanabe; Kaushik Das
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 328 KB
- Volume
- 163
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
This paper describes a cause of the time-dependent degradation of conductivity observed in the representative BIMEVOX phases Bi 2 Cu 0.1 V 0.9 O 5.35 (BICUVOX.10) and Bi 2 Co 0.1 V 0.9 O 5.35 (BICOVOX.10). In both phases, to date, the following facts were reported: the high-temperature stable -type phase transformed reversibly to the low-temperature stable -type phase at 450+5003C through the order+disorder transition without changing to the -type or -type phase. In addition, the degradation of conductivity was observed in -BICUVOX.10 at about 4203C. In the present study, it has turned out that a prolonged annealing at 4503C for several hundred hours causes both phases to change to a new phase with -Bi 4 V 2 O 11 -related structure. Thisrelated phase changes promptly to the phase on heating (at about 5353C for BICOVOX.10 and at about 4853C for BI-CUVOX.10); by contrast, the phase reverts sluggishly to the -related phase. Since the -related phase shows far lower conductivity (10 ؊ 4.8 S cm ؊ 1 at 4303C for BICUVOX.10), this gradual -totransition explains well the time-dependent degradation of conductivity in the phase reported so far. Namely, the phase is metastably quenched to room temperature and reverts gradually to the -related phase upon heat treatment below the -to-transition temperature.