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Large-scale replication of the hierarchical microstructure of bio-template is a long-standing challenge due to the large shrinkage when the bio-templates are burned off. In this work, TiO2 based biomimetic metamaterials have been successfully synthesized by sputtering technique, followed by tape assisted transferring and thermal oxidation process. Tile-like arrays of the scale replicas with ridge-lamellae hierarchical microstructures have been obtained and exhibit bright blue-purple structure color. More interestingly, they exhibit significantly enhanced photocatalytic activity to decompose methylene blue under solar light illumination, with the degradation rate of methylene blue almost five times that of TiO2 thin films with the same sample area. The enhancement on the visible light photocatalytic activity in TiO2 replicas can be attributed to a synergy effect of the presence of Ti3+ doping, the air-TO2 interaction, and hierarchical microstructure. The controlling factors that affect the microstructure, structural color and photocatalytic activity of the TiO2 replicas have been discussed in detail. This work offers a scalable and precise approach to replicate various bio-templates based on transition metal oxides, such as ZnO, Fe3O4, CoO, and VO2, thereby providing the new opportunity for infrared sensing, photocatalytic and photonic applications.

Attempts have been made to manufacture AlON transparent ceramics at low temperature using a new sintering aid system, Y2O3-La2O3-MnO. The sintering behaviors, including relative density and microstructure evolution of AlON ceramics doped with Y2O3-La2O3, MnO alone, and Y2O3-La2O3-MnO were compared. It was found that both the relative densities and grain sizes of samples doped with Y2O3-La2O3-MnO were much higher and larger than those of samples doped with Y2O3-La2O3 or MnO alone, respectively. A liquid phase containing Al, O, N, Mn, and La formed at high temperature and played an important role on both eliminating pores and promoting grain growth of the sintered AlON bodies. Finally, translucent AlON ceramics were obtained through pressureless sintering at 1830 °C for 1 h, ~100 °C lower than those with conventional sintering aid Y2O3-La2O3. The ceramics doped with MnO showed green emission at 534 nm, under 445 nm excitation. We believe Y2O3-La2O3-MnO is a promising additive for the preparation of AlON transparent ceramic at lower temperature.

Transparent AlON ceramics were bonded with Lu-Al-Si-O-N oxynitride glass interlayer at 1450 °C in nitrogen atmosphere in this investigation. The Lu-Al-Si-O-N oxynitride glass showed good wettability on the AlON substrate and had strong interface adhesion with each other. The joining process had no detrimental effect on the in-line transmittance of transparent AlON ceramics but caused slight decrease of flexural strength due to the partial decomposition. The bonding strength of AlON/AlON joint was 142.7 ± 6.3 MPa at room temperature and 110.1 ± 9.6 MPa at 1200 °C in situ, which were comparable with those of the parent AlON ceramics. Some Lu2Si2O7 grains crystallized out from the glass interlayer after joining.

Twin lamellas, were observed in transparent AlON ceramics in our previous work. In this work, the influence of the twin lamellas on mechanical strength was evaluated and its mechanism was investigated by SEM, EBSD, and HRTEM. Both the crystallographic direction and the space direction of a crack will deflect when it propagates across a twin lamella. The dynamic mechanism is that the dislocation propagation in front of the crack tips is blocked by the twin boundaries. Because the fraction of twin boundaries increases with grain size in transparent AlON ceramics, the strengthening effect becomes more notable for large-sized samples resulting in inverse Hall-Petch relation. It is a potentially useful way to advance the mechanical properties of transparent AlON ceramics by controlling the content of twin lamellas.

Raman scattering technique was used to study structure dynamics of strongly reduced epitaxial barium titanate (BaTiO3-x) thin films grown on MgO (1 0 0) substrates by laser molecular beam epitaxy under different oxygen pressures from 10(-2) to 10(-5) Pa. X-ray diffraction and asymmetric rocking curves indicate that lattice parameters c and c/a ratio increase, and a slightly decreases with decreasing oxygen pressure, indicating increased lattice volume of BaTiO3-x thin film. Raman spectra confirm that BaTiO3-x thin films are in tetragonal phase with some deviated features, which maybe origin from tensile strain at film-substrate interface due to lattice parameter mismatch. Moreover, two weak peaks in Raman spectra of BaTiO2.52 thin film grown under 3.0 x 10(-5) Pa may be induced by second-order two-phonon processes. Raman peaks shift towards lower frequencies with decreasing oxygen pressure during deposition, suggesting a decrease of the stress in BaTiO3-x thin films. In the meantime, Raman peaks become broadened, which may be attributed to higher degree of structural disorder in strongly reduced BaTiO3-x lattice structure. (c) 2005 Elsevier Ltd. All rights reserved.