The phase transitions of one-dimensional (1D) anatase TiO2 nanowires were studied by in situ high-pressure synchrotron X-ray diffraction and Raman scattering up to 37 GPa. A direct anatase-to-baddeleyite transformation was observed at ∼9 GPa, which is clearly different from the size-dependent phase transition behaviors for nanocrystalline TiO2. We found the higher compressibility in the c-axis compared to the a-axis for anatase nanowires that may be attributed to both the crystal structural feature and the growth direction of the nanowires. The Ti–O bonds show abnormal changes during the anatase-to-baddeleyite phase transition. This phase transition of the TiO2 nanowires shows obvious morphology-tuned behaviors. Upon decompression, the baddeleyite phase transformed into α-PbO2 phase. The morphology of the TiO2 nanowires shows excellent stability and TiO2 nanowires with α-PbO2 phase were obtained at ambient conditions through a compression–decompression cycle. These results indicate that the nanoscale quasi-1D structure of TiO2 nanowires may contribute to the high-pressure phase transitions showing unique morphology-tuned behaviors.

TiO2 nanosheets with highly reactive {001} facets show ultralow compressibility compared to those of the corresponding TiO2 nanoparticles and bulk.

The high-pressure behavior of zircon-structured YPO 4 (with/without Eu 3+ doping) nanoparticles was examined at room temperature using in situ synchrotron X-ray diffraction (XRD) and photoluminescence (PL) measurements. In contrast with the reported XRD results of bulk YPO 4 upon compression, the nanoparticles showed a distinct transition sequence: zircon phase → scheelite phase (∼18 GPa) without the metastable monazite phase. By the return to ambient pressure, both XRD and PL results revealed that the scheelite phase could be reserved. Further Raman experiments helped us to identify the valuable mode ν 1 (A g ) of the scheelite structure in the quenched samples. The dopants effect, quasi-hydrostatic stress, and nanoscale-induced surface energy difference are considered to explain the high-pressure behavior of the nanoparticles. It is proposed that the nanoscale-induced higher surface energy contribution plays a crucial role in the distinctive high-pressure behavior of the nanoparticles.

As a new class of multi-principal component oxides with high chemical disorder, high-entropy oxides (HEOs) have attracted much attention. The stability and tunability of their structure and properties are of great interest and importance, but remain unclear. By using in situ synchrotron radiation X-ray diffraction, Raman spectroscopy, ultraviolet-visible absorption spectroscopy, and ex situ high-resolution transmission electron microscopy, here we show the existence of lattice distortion in the crystalline (Ce 0.2 La 0.2 Pr 0.2 Sm 0.2 Y 0.2 )O 2−δ HEO according to the deviation of bond angles from the ideal values, and discover a pressureinduced continuous tuning of lattice distortion (bond angles) and band gap. As continuous bending of bond angles, pressure eventually induces breakdown of the long-range connectivity of lattice and causes amorphization. The amorphous state can be partially recovered upon decompression, forming glass-nanoceramic composite HEO. These results reveal the unexpected flexibility of the structure and properties of HEOs, which could promote the fundamental understanding and applications of HEOs.