Phase Transitions of BiVO₄ under High Pressure and High Temperature

Abstract

We have studied the occurrence of phase transitions in two polymorphs of BiVO 4 under high-pressure and high-temperature conditions by means of X-ray diffraction measurements. The fergusonite polymorph undergoes a phase transition at 1.5(1) GPa and room temperature into a tetragonal scheelite-type structure. The same transition takes place at 523(1) K and ambient pressure. A second phase transition takes place at room temperature under compression at 16(1) GPa. The transition is from the tetragonal scheelite structure to a monoclinic structure (space group P2 1 /c). All observed phase transitions are reversible. The zircon polymorph counterpart also transforms under compression into the scheelite-type structure. In this case, the transitions take place at 4.3(1) GPa and room temperature and at 653(1) K and ambient pressure. The zircon−scheelite transition is nonreversible. The experiments support that the fergusonite−scheelite transformation is a second-order transition and that the zircon−scheelite transformation is a first-order transition. Finally, we have also determined the compressibility and the thermal expansion of the fergusonite, scheelite, and zircon phases.

Unraveling the Site-Selective Doping Mechanism in Single-Crystalline BiVO4 Thin Films for Photoelectrochemical Water Splitting

“…Magnified views of the Raman spectra at 368 and 324 cm –1 of pristine BVO, 2% Gd-BVO, and 2% Mo-BVO samples exhibit a clear peak-merging process until 613, 533, and 513 K, respectively, during the heating process (Figure b). For each vibrational mode, the dependence of the Raman shift on temperature can be attributed to the anharmonic coupling of optical phonons and thermal expansion. − Specifically, the magnified plots of the gradual Raman shift at ∼827 cm –1 of the three samples indicate the more regular symmetry of VO 4 tetrahedra during the warming-up process (Figure c). As shown in Figure d–f, we use the linear approximation equation ω­( T ) = ω 0 + κ T to further study the impact of doping on the phase transition temperature.…”

H/F Substitution Induced Enhancement of Phase Transition Temperature and Quantum Yield in Rare-Earth Hybrid Perovskite

“…The TG curves indicate 1 and 2 are thermally stable below 373 K. The structural phase transition of the two hybrids was first performed by differential scanning calorimetry (DSC), while the DSC curves display no reversible endothermic and exothermic peaks in the temperature range of 100–363 K (Figure S3). The phase transition of the two compounds should be a second-order phase transition. − Variable-temperature PXRD (VT-PXRD) patterns were performed to verify the structural phase transitions around 223–343 K. , For 1 , the VT-PXRD patterns show obvious changes upon heating and cooling. It displays peaks changed at 2θ around 14–17°, 18–20°, and 24–27° in HTP (303 K) compared with the LTP (243 K) (Figure a).…”

Tetragonal-zircon BiVO4: a better polymorph for the formation of coherent type-II heterostructures for water splitting applications

“…According to crystal chemistry, the structure of t-z BiVO 4 can be regarded as made up of Bi 3+ cations and VO 2). 53,54 After optimization, the increase in bond length of V-O (1.74 Å) and Bi-O (2.52 Å, 2.42 Å) has been observed. Furthermore, we have calculated the band gap with both functionals, i.e.…”

“…Structural optimization is done with the PBE of GGA and band gap is calculated with both functionals, i.e. PBE of GGA and HSE06 hybrid functional Lattice parameters (A 0 ) Band gap (eV) Our calculated values Literature (experimental values) Literature (computational values) Calculated Literature (experimental values) Literature (computational values) a = b = 7.40, c = 6.47 a = b = 7.303, c= 6.584 a = b = 7.36, c= 6.47 55,56 2.55(PBE) a = b = g = 90 a = b = g = 9053 3.11(HSE06) 2.957 2.9 58 a = b = 7.290, c = 6.444 a = b = g = 9054…”