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 (σ) of the compacted sample is an increasing function of temperature from 363 K to 463 K: evidence is presented that σ derives primarily from proton transfer. The activation energy in this temperature range is Ea ≈ 0.60 eV, while at 363 K, σ = 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. •La(OH)3 powders were prepared via the carbonate route.•La(OH)3powders were compacted into pellets by uniaxial pressing for 72 h.•La(OH)3 ceramics exhibit electrical conductivity 3·10−11 S/cm at 363 K.•Grain boundaries in La(OH)3ceramics are not blocking.