Compression mechanism and pressure-induced amorphization ofγ−ZrW2O8

Abstract

The structure of ␥-ZrW 2 O 8 has been optimized at zero pressure and also at V / V 0 = 0.97 by means of density functional theory calculations using the B3LYP functional. As previously found for ␣-ZrW 2 O 8 , tungsten polyhedra are stiffer than zirconium octahedra in ␥-ZrW 2 O 8 . However, contrary to what has been found for ␣-ZrW 2 O 8 , all first coordination polyhedra in the ␥ phase are less compressible than the unit cell. Volume reduction in ␥-ZrW 2 O 8 is, thus, mainly accomplished by polyhedral tilting. Upon pressure increase, the distance between the terminal oxygen and W atoms from the nearest polyhedra decreases by as much as 3.66% ͑for the pair O101-W6͒. Accordingly, a further reduction in the zirconium tungstate molar volume with the high-pressure transition to the amorphous phase should bring several oxygen atoms within the threshold of bond formation to W. O 1s photoelectron spectra provide further experimental evidence on the formation of additional W-O bonds in amorphous zirconium tungstate. These new W-O bonds should enable the metastable retention of the amorphous phase upon pressure release.

Pressure-induced structural evolution and amorphization in Eu3Ga5O12

“…Previous theoretical and experimental results provide evidence on the distortion and tilting of the tetrahedra as well as an increase of the cation coordination number in the amorphization of these network-structured compounds. 3,5,17,21,22 It has been found that their transition pressures (<10 GPa) are systematically lower than that of the REE garnets (>50 GPa), suggesting a strong influence of the pressure-induced changes of the local oxygen environment around the R site on the amorphization process. Therefore, studying the structural changes of the REE garnets, such as Eu 3 Ga 5 O 12 , can provide new insights into the underlying mechanisms of amorphization in the network-structured compounds.…”

Zirconium tungstate reinforced cyanate ester composites with enhanced dimensional stability

“…At pressures above 200 MPa, ZrW 2 O 8 exists in the g-phase, which is characterized by an orthorhombic crystal structure and the lowest negative CTE values (À1 Â 10 À6 C À1 ); however, the g-phase is metastable and heating the material to 117-140 C at ambient pressure results in an irreversible transformation to the a-phase. [1][2][3][4][5][6][7][8][9] Despite its large negative CTE and interesting phase behavior, only a few researchers have examined the impact of ZrW 2 O 8 as filler in polymer matrix composites. Shi and coworkers 10 reported that the incorporation of 30 volume (vol)% of ZrW 2 O 8 with a polyester resin resulted in a 40% decrease in CTE.…”

Pressure-induced amorphization and decomposition ofFe[Co(CN)6]

“…[24][25][26] It is noteworthy to say that, contrarily to ZrW 2 O 8 and related compounds, Fe͓Co͑CN͒ 6 ͔ does not exhibit terminal atoms that could contribute to retain a possible high-pressure amorphous phase back to ambient pressure. 27 From these considerations, it seems worthwhile to verify to what extent the trend between NTE and PIA also applies to nonoxide structures such as these cyanide-bridged framework materials.…”