We review our work on combinatorial search and investigation of morphotropic phase boundaries (MPBs) in chemically substituted BiFeO 3 (BFO). Utilizing the thin-film composition spread technique, we discovered that rare-earth (RE 5 Sm, Gd, and Dy) substitution into the A-site of the BFO lattice results in a structural phase transition from the rhombohedral to the orthorhombic phase. At the structural boundary, both the piezoelectric coefficient and the dielectric constant are substantially enhanced. It is also found that the observed MPB behavior can be universally described by the average A-site ionic radius as a critical parameter, indicating that chemical pressure effect due to substitution is the primary cause for the MPB behavior in RE-substituted BFO. Our combinatorial investigations were further extended to the A-and B-site cosubstituted BFO in the pseudoternary composition spread of (Bi 1Àx Sm x )(Fe 1Ày Sc y )O 3 . Clustering analysis of structural and ferroelectric property data of the fabricated pseudoternary composition spread reveals close correlations between the structural and ferroelectric properties. We show that the evolution in structural and ferroelectric properties is controlled solely by the A-site Sm substitution and not the B-site Sc substitution.

Triple-stimuli-responsive PEG-based materials are prepared by living anionic ring-opening copolymerization of ethylene oxide and vinyl ferrocenyl glycidyl ether and subsequent thiol-ene postpolymerization modification with cysteamine. The hydrophilicity of these materials can be tuned by three stimuli: (i) temperature (depending on the comonomer ratio), (ii) oxidation state of iron centers in the ferrocene moieties, and (iii) pH-value (through amino groups), both in aqueous solution and at the interface after covalent attachment to a glass surface. In such materials, the cloud point temperatures are adjustable in solution by changing oxidation state and/or pH. On the surface, the contact angle increases with increasing pH and temperature and after oxidation, making these smart surfaces interesting for catalytic applications. Also, their redox response can be switched by temperature and pH, making this material useful for catalysis and electrochemistry applications. Exemplarily, the temperature-dependent catalysis of the chemiluminescence of luminol (a typical blood analysis tool in forensics) was investigated with these polymers.

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