Low-temperature sintering of dense lanthanum silicate electrolytes with apatite-type structure using an organic precipit
- PDF / 1,287,189 Bytes
- 8 Pages / 584.957 x 782.986 pts Page_size
- 29 Downloads / 197 Views
Highly sinterable La10Si6O27 and La10Si5.5M0.5O27 (M = Mg, and Al) nanopowders with apatite-type structure have been synthesized via a homogeneous precipitation method using diethylamine (DEA) as a precipitant. The synthetic approach using an organic precipitant with dispersant characteristics is advantageous in configuring weakly agglomerated nanopowders, leading to desirable sintering activity. X-ray diffraction powder patterns confirmed the single-phase crystalline lanthanum silicate of hexagonal apatite structure at 800 C, which is a relatively lower calcination temperature compared to conventionally prepared samples. Transmission electron microscopy images revealed particles 30 nm in size with a high degree of crystallinity. A dense grain morphology was recognized from the scanning electron microscopy images of the polished surface of the pellets that were sintered at 1400 and 1500 C for 10 h. This low-temperature sintering is significant because conventional powder processing requires a temperature above 1700 C to obtain the same dense electrolyte. The doped-lanthanum silicate electrolyte prepared by the DEA process and sintered at 1500 C for 10 h exhibited electrical conductivity comparable with samples prepared at much higher sintering temperature (>1700 C).
I. INTRODUCTION
Intermediate-temperature solid oxide fuel cells (ITSOFCs), which have operating temperatures ranging from 400 to 700 C, have come to be considered state-of-the-art in the area of power fabrication. This is because of their long-term stability and cost saving potential when produced as large units.1–3 Until recently, conventionally used solid electrolytes with high ionic conductivity consisted of fluorite-structured stabilized zirconia, which requires an operating temperature above 900–1000 C.4–7 Therefore, serious attention has been paid to finding alternative electrolytes for IT-SOFCs, which has led to the development of fluorite and perovskite structures, such as doped ceria and doped lanthanum gallate, respectively.3,4,8–11 However, the application of those materials has been limited by the increase in the electronic conductivity, which occurs in doped-ceria-based electrolytes and by the insufficient chemical stability that characterizes doped lanthanum gallate materials.12
a)
These authors contributed equally to this work. Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0018 b)
J. Mater. Res., Vol. 24, No. 1, Jan 2009
Lanthanum silicate-based compositions that have an apatite-type structure and high electric conductivity have recently attracted significant interest. Initially, Nakayama et al. reported that Ln10xSi6O26þy (Ln = La, Sm, Nd, Dy, Gd, x = 8 to 11) materials with an apatite structure exhibited ionic conductivity.13,14 Among the lanthanum silicate apatite solid electrolytes, the composition of La10Si6O27 has exhibited high oxygen ionic conductivity of >103 Scm1 at 500 C, which is comparably higher than that of 8 mol% yttria doped zirconia (YSZ) electrolytes
Data Loading...
