Increasing Doping Solubility of RE³⁺ Ions in Fergusonite BiVO₄ via Pressure-Induced Phase Transition

Abstract

Eu3+ ions doped bismuth vanadate powders were synthesized by a hydrothermal method, and the effect of Eu3+ ions doping on the crystal structure was investigated by X-ray diffraction (XRD), Raman, and UV–vis diffuse reflectance spectra. XRD and Raman results reveal that the doping solubility of Eu3+ ions in fergusonite-BiVO4 is extremely small. Above 0.5 mol % doping, a structural transition from fergusonite to zircon structure occurs. This phase transition results in band gap enhancement and thus limits its photocatalytic performance. Upon compression, zircon-BiVO4:Eu3+ is not stable, and a zircon-to-scheelite transition presents above 5 GPa. It is noted that this transition is irreversible, and the high-pressure scheelite structure transforms back to the fergusonite structure rather than the original zircon structure after pressure release. The transition sequence of zircon-to-scheelite-to-fergusonite in a compression-decompression cycle for BiVO4:Eu3+ provides one method to synthesize fergusonite-BiVO4:Eu3+ with more doping content. This result confirms that pressure is one effective strategy to access new structures and novel physical properties of functional material.

Structural Phase Transition in BiVO4 Nanosheets under High Pressure

“…Below ∼5 GPa, these initial two peaks (011) and (110) have a tendency to shift to a middle state; above ∼5 GPa, they merge into one single peak (101), indicating that a fergusonite to scheelite transition occurred at ∼5 GPa. The transition pressure is almost three times higher than that in previous reports (∼1.5 GPa). − ,,, At ∼ 10 GPa in the scheelite phase, the slope of the d 101 peak deviates, which can be regarded as a proof of a potential second-order phase transition; more experimental evidence can be found in later sections. Above ∼15 GPa, the (101) peak of the scheelite phase splits into two new peaks, indicating the occurrence of another phase transition.…”

“…The transition pressure is almost three times higher than that in previous reports (∼1.5 GPa). [11][12][13]16,17,21 At ∼ 10 GPa in the scheelite phase, the slope of the d 101 peak deviates, which can be regarded as a proof of a potential second-order phase transition; more experimental evidence can be found in later sections. Above ∼15 GPa, the (101) peak of the scheelite phase splits into two new peaks, indicating the occurrence of another phase transition.…”

Pressure-induced phase transition in α- and β-BiNbO4

“…In our previous research on ABO 4 compounds, such as BiVO 4 , 38,39 ZrGeO 4 40 and LaVO 4 , 41 it is believed that different polymorphic compounds will finally transform into the same high-pressure structure if the pressure is high enough. For example, the fergusonite-and zircon-type BiVO 4 finally transform into the same scheelite-BiVO 4 at high pressure.…”

Phase Transitions of BiVO4 under High Pressure and High Temperature

“…12,38 In our case, we know that T Trans = 523(1) K. In Figure 9, we show ε s and β90°versus temperature and fits using functions of the form ε s = A(|T − T Trans |) n and β90°= A(|T − T Trans |) n . In the first case, the best fit is obtained for n = 0.56 (7). In the second case, it is obtained for n = 0.48 (11).…”

“…Bismuth vanadate (BiVO 4 ) has recently been under focus for its potential use in photocatalysis for hydrogen production via water splitting. , It has also attracted attention for decades because of its complex structural phase diagram, tunable properties when being doped, − its rich polymorphism depending on preparation conditions, and external thermodynamic parameters . The high-pressure (HP) and high-temperature (HT) behavior of BiVO 4 has attracted attention for nearly half a century. , This compound is known to crystallize either into the stable monoclinic fergusonite-type polymorph (space group I 2/ a ) or in the metastable tetragonal zircon-type polymorph (space group I 4 1 / amd ) .…”