Sintered polycrystalline cobalt ferrite is a potential magnetostrictive smart material for applications as sensors and actuators. A novel concept of enhancing the magnetostrictive strain of sintered cobalt ferrite by making self-composites from nanosized and bulk powders with different particle sizes of the same material as components is reported. The self-composites give higher magnetostriction coefficient and strain derivative when compared to the sintered products obtained from the individual powders. The individual components give a maximum magnetostriction up to ~310 ppm, whereas up to ~370 ppm is obtained for a two-component system consisting of powders of two different sizes. On the other hand, a three-component self-composite made from starting powders of 3 nm, 40 nm and >1 μm give very high magnetostriction of ~400 ppm at 800 kA/m, suitable for making devices.

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Low-temperature hydrothermal epitaxial growth and topochemical conversion (TC) reactions offer unexploited possibilities for the morphological engineering of heterostructural and non-equilibrium shape (photo)catalyst particles. The hydrothermal epitaxial growth of SrTiO 3 on Bi 4 Ti 3 O 12 platelets is studied as a new route for the formation of novel nanoheterostructural SrTiO 3 /Bi 4 Ti 3 O 12 platelets at an intermediate stage or (100)-oriented mesocrystalline SrTiO 3 nanoplatelets at the completed stage of the TC reaction. The Bi 4 Ti 3 O 12 platelets act as a source of Ti(OH) 6 2– species and, at the same time, as a substrate for the epitaxial growth of SrTiO 3 . The dissolution of the Bi 4 Ti 3 O 12 platelets proceeds faster from the lateral direction, whereas the epitaxial growth of SrTiO 3 occurs on both bismuth-oxide-terminated basal surface planes of the Bi 4 Ti 3 O 12 platelets. In the progress of the TC reaction, the Bi 4 Ti 3 O 12 platelet is replaced from the lateral ends toward the interior by SrTiO 3 , while Bi 4 Ti 3 O 12 is preserved in the core of the heterostructural platelet. Without any support from noble-metal doping or cocatalysts, the SrTiO 3 /Bi 4 Ti 3 O 12 platelets show stable and 15 times higher photocatalytic H 2 production (1265 μmol·g –1 ·h –1 ; solar-to-hydrogen (STH) efficiency = 0.19%) than commercial SrTiO 3 nanopowders (81 μmol·g –1 ·h –1 ; STH = 0.012%) in pH-neutral water/methanol solutions. A plausible Z scheme is proposed to describe the charge-transfer mechanism during the photocatalysis.

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