Size Dependent Melting for Transient Liquid Phase Sintering of Nanoceramics

• Research unit: COST
• Project number: C00.0038

Key words (English)

Ceria solid solutions; sintering; activation energy; grain growth; conductivity

Research programs (English)

COST-Action 525 - Advanced Electron Ceramics: Grain Boundary Engineering

Short description (English)

See abstract

Further information (English)

Full name of research-institution/enterprise: ETH Zürich Prof. f. Nichtmetallische Anorganische Werkstoffe ETH Hönggerberg HCI G 535

Partners and International Organizations (English)

A, B, CZ, DK, F, D, IRL, I, LV, LT, N, P, SI, E, S, CH, TR, GB

Abstract (English)

Ceria solid solutions exhibit 4 to 5 times higher ionic conductivity at intermediate temperatures (600 - 700 °C) compared to zirconia-based solid solutions. Therefore, solid oxide fuel cells with ceria electrolytes can be operated at temperatures as low as 700 °C with high power output and high efficiency. Ceria is partially reduced in the atmosphere present at the fuel cell anode leading to mixed ionic-electronic conductivity and increased electrode performance. Conventional sintering of ceria requires high temperatures leading to partial reduction above 1200°C and therefore to reduced sintering kinetics. Sintering of nanosized ceria and CeO.8Gd0.2O1.9 (CGO) with and without cobalt oxide doping is studied. The high shrinkage rates of cobalt oxide doped powders at temperatures as low as 900 °C lead to dense, nano-grain sized ceria solid solutions. Shrinkage rates from sintering experiments with constant rates of heating were analysed with classical sintering models. Characteristic differences in the parameters of classical sintering models were obtained due to the cobalt oxide doping of CGO. It is suggested that cobalt oxide doping suppresses surface diffusion and promotes grain boundary diffusion leading to a fine-grained microstructure. Grain growth studies have shown that the grain boundary mobility is increased due to the cobalt oxide doping indicating increased diffusion rates at the grain boundaries. Conductivity measurements have revealed the existence of a percolating network of a CoO-rich grain boundary phase at 900 °C leading to an increased conductivity at low temperatures. The network is destroyed in slowly cooled samples where the secondary grain boundary phase retracts to the grain boundary triple points to form isolated particles.

References in databases (English)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C00.0038