Electrical conductivity of lanthanum hydroxide below 473 K

We have investigated the synthesis, preparation protocols and properties of La(OH)3 powder and pellets. Preparation of useful pellet samples of La(OH)3 from the synthesized powder required (i) elimination of the presence of carbonate oxides by powder calcination at 1173 K in flowing oxygen; followed by (ii) hydration of the remaining La2O3 in boiling, deionized water for 48 h. Room temperature compaction of these powders into solid pellet samples with 73% of theoretical density, suitable for electrical measurements, requires prolonged (72 h) dwell under 80 MPa uniaxial pressure, suggesting that cold sintering and formation of inter-grain bridges do take place. The electrical conductivity (Sigma) of the compacted sample is an increasing function of temperature from 363 K to 463 K: evidence is presented that Sigma derives primarily from proton transfer. The activation energy in this temperature range is Ea approximate to 0.60 eV, while at 363 K, Sigma = 3.10-11 S/cm. Although 3.10-11 S/cm is too low for applications in fuel cells it may be sufficient for electro-chemo-mechanical applications. The fact that the grain boundaries are apparently not blocking, makes it attractive to look for dopants that may potentially enhance the low temperature conductivity.

Automated summary

The study focused on the synthesis, preparation protocols and properties of La(OH)3 powder and pellets, highlighting the potential for cold sintering and inter-grain bridges formation under high pressure. The electrical conductivity was found to be temperature-dependent, primarily deriving from proton transfer, suggesting the potential use of dopants to enhance low temperature conductivity.