The high-pressure (HP) behavior of Fe­(IO3)3 was studied up to 35 GPa using powder X-ray diffraction, infrared micro-spectroscopy, and ab initio density-functional theory calculations. Fe­(IO3)3 shows a pressure-induced structural phase transition at 15–22 GPa. Powder X-ray diffraction was employed to obtain the structure of the HP phase. This phase can be described by the same space group (P63) as the low-pressure phase but with a substantial different c/a ratio. This conclusion is supported by our computational simulations. The discovered phase transition involves a large volume collapse and a change in the coordination polyhedron of iodine, being a first-order transition. It also produces substantial changes in the infrared and Raman vibrational spectra. The pressure dependences of infrared and Raman phonon frequencies and unit-cell parameters have been obtained. A mode assignment is proposed for phonons based upon ab initio calculations. The bulk modulus of the two phases was obtained by fitting a Birch–Murnaghan equation of state to synchrotron X-ray powder diffraction data resulting in B 0 = 55(2) GPa for the low-pressure phase and B 0 = 73(9) GPa for the HP phase. Calculations gave B 0 = 36(1) GPa and B 0 = 48(3) GPa for the same phases, respectively. The results are compared with other iodates, in particular LiIO3, for which we have also performed density-functional theory calculations. A possible mechanism driving the observed phase transition will be discussed.

A pressure-induced structural phase transition and its intimate link with the superconducting transition was studied for the first time in TiSe2 up to 40 GPa at room temperature using X-ray diffraction, transport measurement, and first-principles calculations. We demonstrate the occurrence of a first-order structural phase transition at 4 GPa from the standard trigonal structure (S.G.P3̅m1) to another trigonal structure (S-G-P3̅c1). Additionally, at 16 GPa, the P3̅c1 phase spontaneously transforms into a monoclinic C2/m phase, and above 24 GPa, the C2/m phase returns to the initial P3̅m1 phase. Electrical transport results show that metallization occurs above 6 GPa. The charge density wave observed at ambient pressure is suppressed upon compression up to 2 GPa with the emergence of superconductivity at 2.5 GPa, with a critical temperature (T c) of 2 K. A structural transition accompanies the emergence of superconductivity that persists up to 4 GPa. The results demonstrate that the pressure-induced phase transitions explored by the experiments along with the theoretical predictions may open the door to a new path for searching and controlling the phase diagrams of transition metal dichalcogenides.

Inverse photoconductivity (IPC) is a unique photoresponse behavior that exists in few photoconductors in which electrical conductivity decreases with irradiation, and has great potential applications in the development of photonic devices and nonvolatile memories with low power consumption. However, it is still challenging to design and achieve IPC in most materials of interest. In this study, pressure‐driven photoconductivity is investigated in n‐type WO3 nanocuboids functionalized with p‐type CuO nanoparticles under visible illumination and an interesting pressure‐induced IPC accompanying a structural phase transition is found. Native and structural distortion induced oxygen vacancies assist the charge carrier trapping and favor the persistent positive photoconductivity beyond 6.4 GPa. The change in photoconductivity is mainly related to a phase transition and the associated changes in the bandgap, the trapping of charge carriers, the WO6 octahedral distortion, and the electron–hole pair recombination process. A unique reversible transition from positive to inverse photoconductivity is observed during compression and decompression. The origin of the IPC is intimately connected to the depletion of the conduction channels by electron trapping and the chromic property of WO3. This synergistic rationale may afford a simple and powerful method to improve the optomechanical performance of any hybrid material.

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