Bench- and pilot-scale continuous-flow hydrothermal production of barium strontium titanate nanopowders

•Continuous-flow hydrothermal synthesis of barium titanate nanopowders.•Base is necessary for the generation of the crystalline perovskite.•Barium strontium titanate nanoparticles produced across the targeted full stoichiometric range.•Products are substoichiometric single phase crystalline nanoparticles.•Pilot-scale production of perovskite nanoparticles.

Barium strontium titanate (Ba(1−x)SrxTiO3) nanopowders have been prepared at both bench- and pilot-scales using a fully hydrothermal continuous-flow system. A mixed solution of barium nitrate (and/or strontium nitrate) with titanium bis (ammonium lactato) dihydroxide was mixed in-flow with a sodium hydroxide stream before meeting a pre-heated flow of supercritical water at a counter-current mixing point which resulted in the crystallisation of Ba(1−x)SrxTiO3. The obtained nanopowders were characterised by ICP-MS, powder X-ray diffraction, transmission electron microscopy and Raman spectroscopy. All products were found to be sub-stoichiometric with the total M2+:Ti ratio varying between 0.8:1 and 0.96:1, attributed to the formation of divalent metal carbonates preventing full incorporation of the M2+ ions into the perovskite structure in the extremely short reaction times employed. The obtained products were found to adopt the expected perovskite structure, while increasing strontium content led to a decrease in both particle size and lattice parameter. Products with target compositions of Ba(1−x)SrxTiO3 (0 ⩽ x ⩽ 1) were produced for the first time by a fully hydrothermal route at both the bench-scale of ∼5 g h−1 and pilot-scale at ∼80 g h−1.

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