Pressure-induced structural phase transitions and amorphization in selected molybdates and tungstates

Mączka, M.; Filho, A. G. Souza; Paraguassu, W.; Freire, Paulo; Fílho, J. Mendes; Hanuza, J.

doi:10.1016/j.pmatsci.2012.01.001

Cited by 111 publications

(71 citation statements)

References 141 publications

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“…Note that the energy gap between stretching and bending modes of BaWO 4 decreases from about 440 cm -1 at ambient pressure to only 85 cm -1 at 9.4 GPa. The latter is a direct proof of the change of coordination of tungsten, from tetrahedral to octahedral, associated to the phase transition [36]. Upon further compression, we did not find any qualitative change in the Raman spectrum of BaWO 4 -II.…”

Section: A Xrd Experimentssupporting

confidence: 48%

Complex high-pressure polymorphism of barium tungstate

et al. 2012

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We have studied BaWO 4 under compression at room temperature by means of x-ray diffraction and Raman spectroscopy. When compressed with neon as pressuretransmitting medium (quasi-hydrostatic conditions), we found that BaWO 4 transforms from its low-pressure tetragonal structure into a much denser monoclinic structure. This result confirms our previous theoretical prediction based on ab initio calculations that the scheelite to BaWO 4 -II transition occurs at room temperature if kinetic barriers are suppressed by pressure. However, our experiment without any pressure-transmitting medium has resulted in a phase transition to a completely different structure, suggesting non-hydrostaticity may be responsible for previously reported rich polymorphism in BaWO 4 . The crystal structure of the low-and high-pressure phases from the quasihydrostatic experiments has been Rietveld refined. Additionally, for the tetragonal phase the effects of pressure on the unit-cell volume and lattice parameters is discussed.2 Finally, the pressure evolution of the Raman modes of different phases is reported and compared with previous studies.

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Section: A Xrd Experimentssupporting

confidence: 48%

Complex high-pressure polymorphism of barium tungstate

et al. 2012

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“…This attention is due to the catalytic activity of (MoO 4 2− ) groups in hydrocarbons oxidations [17][18][19][20] and due to negative thermal expansion, ferroelasticity, and pressure-induced amorphization [21]. Furthermore, the interpretation of laser properties needs knowledge of vibrational level distribution [22].…”

Section: Introductionmentioning

confidence: 99%

Electrical and Vibrational Studies of Na₂K₂Cu(MoO₄)₃

Dridi

Zid

Mączka

2017

Advances in Materials Science and Engineering

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The complex impedance of Na 2 K 2 Cu(MoO 4 ) 3 material has been investigated in the temperature range of 653-753 K and in the frequency range of 40 Hz-5 MHz. Electrical behavior of the studied material is explained through an equivalent circuit model which takes into account the contributions of grains and grains boundaries. The number of vibrational modes was calculated using group theoretical approach. The infrared and Raman spectra have also been measured and vibrational assignment has been proposed.

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“…Lanthanum tritungstate belongs to the A 2 (BO 4 ) 3 family of compounds, a large group which includes materials with optical, ferroelastic, and ferroelectric properties, which make them useful in diverse technological fields [1]. Under normal conditions, the rare-earth (RE) tritungstates and trimolybdates RE 2 (MO 4 ) 3 (M = W, Mo) adopt different crystalline structures depending on both the RE cation as well as the method used during the synthesis.…”

Section: Introductionmentioning

confidence: 99%

“…Other structures with SG P 2 1 /c, No. 14, and Z = 4 are found in related compounds like Bi 2 (MoO 4 ) 3 , Sb 2 (SO 4 ) 3 , and As 2 (SO 4 ) 3 [1]. Trimolybdates and tritungstates with heavier RE cations (RE = Ho-Lu) adopt the γ form of Sc 2 (WO 4 ) 3 and display negative thermal expansion (NTE) [4][5][6].…”

Section: Introductionmentioning

confidence: 99%

“…The α phases of trimolybdates have been less studied than the β or γ phases, as evidenced in a recent review by Maczca et al on pressure-induced phase transitions and amorphization in the tungstate and molybdate families [1]. In fact, the α phases of tritungstates RE 2 (WO 4 ) 3 (RE = La-Dy) have never been investigated under compression.…”

Section: Introductionmentioning

confidence: 99%

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Effect of pressure onLa2(WO4)3with a modulated scheelite-type structure

et al. 2014

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We have studied the effect of pressure on the structural and vibrational properties of lanthanum tritungstate La 2 (WO 4 ) 3 . This compound crystallizes under ambient conditions in the modulated scheelite-type structure known as the α phase. We have performed x-ray diffraction and Raman scattering measurements up to a pressure of 20 GPa, as well as ab initio calculations within the framework of the density functional theory. Up to 5 GPa, the three methods provide a similar picture of the evolution under pressure of α-La 2 (WO 4 ) 3 . At 5 GPa, we begin to observe some structural changes, and above 6 GPa we find that the x-ray patterns cannot be indexed as a single phase. However, we find that a mixture of two phases with C2/c symmetry accounts for all diffraction peaks. Our ab initio study confirms the existence of several C2/c structures, which are very close in energy in this compression range. According to our measurements, a state with medium-range order appears at pressures above 9 and 11 GPa, from x-ray diffraction and Raman experiments, respectively. Based upon our theoretical calculations we propose several high-pressure candidates with high cationic coordinations at these pressures. The compound evolves into a partially amorphous phase at pressures above 20 GPa.

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Pressure-induced structural phase transitions and amorphization in selected molybdates and tungstates

Cited by 111 publications

References 141 publications

Complex high-pressure polymorphism of barium tungstate

Complex high-pressure polymorphism of barium tungstate

Electrical and Vibrational Studies of Na₂K₂Cu(MoO₄)₃

Effect of pressure onLa2(WO4)3with a modulated scheelite-type structure

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Pressure-induced structural phase transitions and amorphization in selected molybdates and tungstates

Cited by 111 publications

References 141 publications

Complex high-pressure polymorphism of barium tungstate

Complex high-pressure polymorphism of barium tungstate

Electrical and Vibrational Studies of Na2K2Cu(MoO4)3

Effect of pressure onLa2(WO4)3with a modulated scheelite-type structure

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Product

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Electrical and Vibrational Studies of Na₂K₂Cu(MoO₄)₃