Investigation of structural changes in the phase transformations of γ-Bi₂MoO₆

Abstract

In this work, extensive thermo-Raman investigations have been carried out on a γ(L)-Bi2MoO6 sample (`(L)' indicating the low-temperature polymorph) in an effort to gain an understanding of the structural evolution and phase transformation involved during a dynamical thermal process. The room temperature Raman spectrum of the γ(L)-Bi2MoO6 phase indicated the presence of corner-sharing distorted MoO6 octahedra. The spectral variations, shift in the band positions, decrease in intensities and broadening of the Mo-O modes observed in the thermo-Raman spectra and the thermal evolution of the Mo-O bonds in the temperature interval from 25 to 610 °C strongly suggest that the transformation from the γ(L)-Bi2MoO6 to the γ(I)-Bi2MoO6 phase (`(I)' indicating the intermediate-temperature polymorph) involves a gradual anisotropic thermal response of Mo-O bonds initially, upon heating, and further appreciable increase in the octahedral distortion from 310 °C onwards - until the structure is on the verge of becoming composed of distorted tetrahedra. The spectral variation in the thermo-Raman spectra observed for the transformations to γ(H)-Bi2MoO6 (`(H)' indicating the high-temperature polymorph) starting at around 620 °C and ending at 660 °C revealed the sluggish nature of the transformations and also clearly indicated the transformation from highly distorted MoO6 octahedra to distorted tetrahedra. The comparison of the profile of the Raman spectrum of the γ(H)-Bi2MoO6 phase measured at 720 °C and that measured after cooling down to 25 °C clearly rules out the possibility of the formation of a β-Bi2Mo2O9} phase structure consisting of Mo6+ in tetrahedral coordination at high temperature.

Photoelectrochemical degradation of anti-inflammatory pharmaceuticals at Bi2MoO6–boron-doped diamond hybrid electrode under visible light irradiation

“…There is a sharp peak around 1334 cm À1 , slightly away from the characteristic signature of the diamond structure, 1332 cm À1 , revealing the presence of diamond [10]. The peak around 800 and 1000 cm À1 are attributed to Bi 2 MoO 6 crystal [26,27]; XRD analysis of BDD and the hybrid electrode was shown in Fig. 2, the peak at 28.3u is produced from the Bi 2 MoO 6 (JCPDS.…”

Refinement of Bi2WO6 and Bi2MoO6 polymorphism

“…According to Watanabe and Kodama [13], this transition is also seen at 604 • C in differential thermal analysis (DTA) scans as a weak thermal event owing to the proximity of this transition to the second order transition. According to several reports [10,[15][16][17], -phase persists only to 310-350 • C. It seems likely that, at these temperatures, BM undergoes a phase transition → into the phase, which we designate as . This transition is evidenced by the X-ray investigations [15], changes in its Raman spectrum [16,17].…”

“…At higher temperatures it has transformed into tetragonal nonpolar phase (4/mmm) [5]. The phase transitions of BW and BM have been studied for more than four decades now, but the number of transitions and their detailed nature are not yet fully clear [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

Bi2MoO6 Nanostrip Networks for Enhanced Visible‐Light Photocatalytic Reduction of CO2 to CH4

“…[1,2] Bismuth molybdates are of the general chemicalf ormula Bi 2 O 3 ·n MoO 3 ,w here n = 3, 2, or 1, corresponding to the a, b,a nd g phases, respectively. [3,4] The structures of the a and b phases can be considered as defective fluorite structures, whereas the g phase is an Aurivillius type structure, which consists of alternating layers of (Bi 2 O 2 ) 2 + and (MoO 4 ) 2À . [3][4][5] The g phase is of particular interest, since this material is not only ag ood catalyst, but also shows an unusual phase transformation above 600 8Ct ot he g' phase which further transformst ot he g'' phase.…”

“…[3,4] The structures of the a and b phases can be considered as defective fluorite structures, whereas the g phase is an Aurivillius type structure, which consists of alternating layers of (Bi 2 O 2 ) 2 + and (MoO 4 ) 2À . [3][4][5] The g phase is of particular interest, since this material is not only ag ood catalyst, but also shows an unusual phase transformation above 600 8Ct ot he g' phase which further transformst ot he g'' phase. [3] The g-Bi 2 MoO 6 ,k nown as "koechlinite", [4] is ak ind of visible-light-responsive photocatalyst, widely being applied in the degradation of organic pollutants, [6][7][8][9][10][11][12][13][14][15][16][17][18][19] photocatalytic oxygen evolution, [20][21][22][23] and the photocatalytic reduction of CO 2 .…”