Pressure Induced Phase Transitions in Alkaline Earth Tungstates

Christofilos, D.; Ves, S.; Kourouklis, G. A.

doi:10.1002/pssb.2221980172

Cited by 53 publications

(92 citation statements)

References 12 publications

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“…On the other hand, B cations, tungsten (W) and lithium (Li), are coordinated by four X anions forming relatively isolated BX 4 tetrahedral units [7]. In the cation coordination notation for ABX 4 compounds ([cation A coordination -cation B coordination]), scheelites have cation coordination [8 -4]. Fig.…”

Section: )mentioning

confidence: 99%

“…The spectrum is plotted together with the difference between the measured data and the calculated profile with the aim of illustrating the quality of the structural refinements used to extract the lattice parameters and bond lengths of CaWO 4 here presented. In order to obtain the lattice parameters from the experimental data the Le Bail extraction technique [15] available in the GSAS programme [16] was employed.…”

Section: )mentioning

confidence: 99%

“…The bond distances for CaWO 4 were calculated after performing the structural refinements using the POWDERCELL programme package [17]. The analogous data on YLiF 4 , used for the comparative analysis of the pressure effects on the scheelite compounds CaWO 4 and YLiF 4 , were obtained from Ref. [5].…”

Section: )mentioning

confidence: 99%

“…In order to know the microscopic mechanisms governing the scheelite-tomonoclinic phase transitions in CaWO 4 and YLiF 4 we have analyzed the pressure dependence of the lattice parameters and bond distances in these two compounds. Fig.…”

Section: Pressure Effects On the Local Atomic Structurementioning

confidence: 99%

“…Many ABX 4 ]. In both compounds, the reversibility to the initial scheelite structure after decreasing pressure has been shown.…”

Section: Introductionmentioning

confidence: 99%

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Effects of pressure on the local atomic structure of CaWO4 and YLiF4: mechanism of the scheelite-to-wolframite and scheelite-to-fergusonite transitions

Errandonea

Manjón

Somayazulu

et al. 2004

Journal of Solid State Chemistry

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Section: )mentioning

confidence: 99%

Section: )mentioning

confidence: 99%

Section: )mentioning

confidence: 99%

Section: Pressure Effects On the Local Atomic Structurementioning

confidence: 99%

“…Many ABX 4 ]. In both compounds, the reversibility to the initial scheelite structure after decreasing pressure has been shown.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Effects of pressure on the local atomic structure of CaWO4 and YLiF4: mechanism of the scheelite-to-wolframite and scheelite-to-fergusonite transitions

Errandonea

Manjón

Somayazulu

et al. 2004

Journal of Solid State Chemistry

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CaWO4: A New High-Pressure and High-Temperature Phase

Errandonea¹,

Somayazulu²,

Häusermann³

2002

phys. stat. sol. (b)

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Subject classification: 61.50.Ks Scheelite-type AWO 4 binary oxides are important materials due to their use as scintillator detectors, photoanodes, solid laser hosts, and in optical fiber applications. They crystallize in the scheelite structure (SG: I4 1 /a, No. 88) [1], which may be regarded as a cubic close-packed array of A 2þ and [WO 4 ] 2-units with the coordination number of 8 and 4 oxygen atoms for the A and W cations, respectively. CaWO 4 and other tungstates have been studied by high-pressure Raman spectroscopy [2], the occurrence of pressure-induced structural transitions being detected. In addition, the room temperature (RT) phase behaviour of CaWO 4 has been studied by X-ray diffraction up to 65 GPa [3]. These diffraction studies have determined that a pressure-induced transition to the wolframite-type structure (SG: P2/c, No. 13) takes place at 12 GPa [3] and have also established that CaWO 4 becomes amorphous at pressure exceeding 40 GPa [3]. At high pressure and high temperature a new phase has been found in BaWO 4 [4] and PbWO 4 [5], having a characteristic dense structure. In this note, we report the observation of a quenchable new high-pressure and high-temperature phase of CaWO 4 at 45 GPa after heating to 477 K.The existence of this new phase was verified by energy dispersive X-ray powder diffraction (EDXD), using a focused beam of 10 mm by 10 mm, and its structure was tentatively determined using the XRDA [6] and GSAS [7] program packages. These studies were carried out at the X-17C beam line at the National Synchrotron Light Source (NSLS) using a white beam and a Ge detector. The powder X-ray patterns were all collected at a diffraction angle of 2q ¼ 13 . CaWO 4 powder (99.78% purity) was compressed in a diamond anvil cell (DAC) to 45 GPa. No pressure medium was used in the experiments because it is known that alkaline earth tungstates are soft and can act as their own pressure medium [3,8]. A gold standard (99% purity), which was used for pressure calibration, was loaded along with the sample. We compressed the crystalline CaWO 4 sample until reaching the amorphization of it [3]. At 45 GPa CaWO 4 was already amorphized, but after heating the DAC to 477 K during two hours in an off-line electrical furnace, and then quenching to RT, the crystalline structure was recovered, being the final new phase we obtained. This is illustrated in Fig. 1, where a sequence of the diffraction spectra obtained at 2 GPa and 45 GPa at RT as well as at 45 GPa after heating is shown. After releasing pressure, no other changes that shift the peaks to lower energies were observed in the X-ray diffraction pattern indicating that the new phase remains stable at ambient pressure.A typical X-ray diffraction pattern for the new phase is given in Fig. 2. The general characteristics of the powder pattern are quite different from those of the scheelite and wolframite phase [3]. Decomposition of CaWO 4 can be ruled out since similar tungstates are thermodynamically stable with respect to their component oxides (CaO and WO...

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Raman spectroscopy of the molybdate minerals chillagite (tungsteinian wulfenite‐I4), stolzite, scheelite, wolframite and wulfenite

Crane

Frost

Williams

et al. 2002

J Raman Spectroscopy

103

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Raman spectra of chillagite, wulfenite, stolzite, scheelite and wolframite were obtained at 298 and 77 K using a Raman microprobe in combination with a thermal stage. Chillagite is a solid solution of wulfenite and stolzite. The spectra of these molybdate minerals are orientation dependent. The band at 695 cm −1 is interpreted as an antisymmetric bridging mode associated with the tungstate chain. The bands at 790 and 881 cm −1 are associated with the antisymmetric and symmetric A g modes of terminal WO 2 whereas the origin of the 806 cm −1 band remains unclear. The n 4 .E g / band was absent for scheelite. The bands at 353 and 401 cm −1 are assigned as either deformation modes or as r(B g ) and d.A g / modes of terminal WO 2 . The band at 462cm −1 has an equivalent band in the infrared at 455 cm −1 assigned as d as .A u / of the .W 2 O 4 / n chain. The band at 508 cm −1 is assigned as n sym .B g / of the .W 2 O 4 / n chain.

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Pressure Induced Phase Transitions in Alkaline Earth Tungstates

Cited by 53 publications

References 12 publications

Effects of pressure on the local atomic structure of CaWO4 and YLiF4: mechanism of the scheelite-to-wolframite and scheelite-to-fergusonite transitions

Effects of pressure on the local atomic structure of CaWO4 and YLiF4: mechanism of the scheelite-to-wolframite and scheelite-to-fergusonite transitions

CaWO4: A New High-Pressure and High-Temperature Phase

Raman spectroscopy of the molybdate minerals chillagite (tungsteinian wulfenite‐I4), stolzite, scheelite, wolframite and wulfenite

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