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Atomically thin diamond, also called diamane, is a twodimensional carbon allotrope and has attracted considerable scientific interest because of its potential physical properties. However, the successful synthesis of a pristine diamane has up until now not been achieved. We demonstrate the realization of a pristine diamane through diamondization of mechanically exfoliated few-layer graphene via compression. Resistance, optical absorption, and X-ray diffraction measurements reveal that hexagonal diamane (h-diamane) with a bandgap of 2.8 ± 0.3 eV forms by compressing trilayer and thicker graphene to above 20 GPa at room temperature and can be preserved upon decompression to ∼1.0 GPa. Theoretical calculations indicate that a (−2110)-oriented h-diamane is energetically stable and has a lower enthalpy than its few-layer graphene precursor above the transition pressure. Compared to gapless graphene, semiconducting h-diamane offers exciting possibilities for carbon-based electronic devices.

We report the superconductivity enhancement of ZrTe on compression up to 33 GPa. The superconducting transition occurs above 4.1 GPa and the superconducting temperature (T ) increases with pressure in further compression, reaching a maximum of 7.1 K at ~28 GPa. An anomalous change of superconducting temperature is seen in the compression above 21 GPa. No structural phase transition is observed in the whole compression up to 36 GPa, but a subtle change in structural parameter is seen between 17-19 GPa, which seems relevant to the anomalous increase in the superconducting temperature. First-principle calculations reveal that the density of states at the Fermi level increases with pressure, which explains the enhancement of T in ZrTe under compression.

Jahn-Teller distortion commonly exists in Cu-containing complex oxides and remarkably changes the electronic property. However, how it functions to pressure in high-entropy oxides (HEOs) remains unknown. Here we studied pressure engineering on quenching the Jahn-Teller distortion in the (Mg 0.2 Ni 0.2 Co 0.2 Zn 0.2 Cu 0.2 )O HEO and its effect on the electronic structure. Synchrotron X-ray diffraction demonstrate that the local structural distortion of the CuO 6 octahedral sublattice in the rocksalt-type (Mg 0.2 Ni 0.2 Co 0.2 Zn 0.2 Cu 0.2 )O HEO is progressively reduced and the distorted structure evolves into a nearly ideal form with increasing pressure up to 40 GPa. Alternating current impedance and ultraviolet-visible absorption reveal a dramatic resistance drop by more than 3 orders of magnitude and an obvious bandgap decrease of ~0.1 eV, accompanied by the pressure-induced quenching of the Jahn-Teller distortion in the (Mg 0.2 Ni 0.2 Co 0.2 Zn 0.2 Cu 0.2 )O HEO. Our study presents a high-pressure route for tuning the local structural distortion and electronic structure of Cu-containing HEOs for optimizing the materials functionality.

The comprehension of structural behaviors in double perovskites is crucial for their functional optimization, especially when applying external regulations. Here, to inquire about potential structures with better magnetic performance, high-pressure phase transformation in double perovskite Ba 2 SmBiO 6 was first investigated up to 50 GPa via in situ high-pressure x-ray diffraction and Raman spectroscopy. A pressure-induced phase transition from cubic Fm-3m to orthorhombic Pnma is discovered at 4.8 GPa, accompanied by the splitting of the diffraction peaks. Above 19.8 GPa, the new phase becomes distorted as shown by the peak recombination and broadening. The variation of Raman spectra also confirms the formation and distortion of the high-pressure phase during compression, through the evolution of Bi-O stretching, Bi-O bending, octahedral rotation, and Ba-sites translation modes. The analysis of tilt angles and distortion factor evinced that the octahedral BiO 6 tilting is the key factor for the phase transition occurrence. Based on the Mulliken populations analyses, the Bi-O bonds undergo a covalent-ionic-antibonding transition across the phase transition under compression. Our exploration of the phase transition mechanism guides the modulation of the magnetic and electronic properties under extreme conditions.

In this paper, we introduced a method to measure grain rotation of nanomaterials under external stress using a high pressure diamond anvil cell and the Laue microdiffraction technique at a synchrotron facility. We used WC tungsten carbide marker crystals to investigate grain rotation activities of 3 nm and 500 nm nickel media. Our results show that the grain rotation of 3 nm and 500 nm nickel nanocrystals increase with pressure and finally rotation of 500 nm nickel tends to stop at a lower pressure/stress level than 3 nm nickel saturate around 5 GPa and 3 GPa, respectively. 3 nm nickel nanocrystals show a higher rotation magnitude than 500 nm nickel nanocrystals. Our measurements show an effective method to study the grain rotation of nanomaterials especially in ultrafine nanocrystals.

Nanoceramics may have different structural and physical properties compared to their coarse-grained counterparts. Here, we report the high-pressure study of micro- and nano-crystalline MgAl2O4 in order to examine the effect of particle size on the structural stability. A reversible pressure-induced phase transition (cubic to tetragonal) is observed in MgAl2O4 nanocrystals under non-hydrostatic pressure at room temperature, in contrast to the previously reported structural transition of MgAl2O4 at high pressure and high temperature. It is also found that the compressed MgAl2O4 microcrystals do not fracture further below 60 nm, suggesting a plastic deformation mechanism transition. MgAl2O4 with a grain size above ∼60 nm exhibits normal cracking behaviors, but shows metal-like plastic deformation behaviors below this critical size. It is implied that combined ductility and strength can be achieved in nanoceramic MgAl2O4.