High pressure synchrotron x-ray powder diffraction study of Sc₂Mo₃O₁₂and Al₂W₃O₁₂

Abstract

Synchrotron x-ray powder diffraction was used to study Sc 2 Mo 3 O 12 and Al 2 W 3 O 12 at high pressure in a DAC. Both compounds adopt the orthorhombic Sc 2 W 3 O 12 structure under ambient conditions and exhibit anisotropic negative thermal expansion. A phase transition from orthorhombic (Pnca) to monoclinic (P2 1 /a) symmetry was observed at ∼0.25 GPa for Sc 2 Mo 3 O 12 and at ∼0.1 GPa for Al 2 W 3 O 12 associated with a volume reduction of ∼1.5-2%. A second crystalline to crystalline phase transition was clearly seen only for Sc 2 Mo 3 O 12 (2.5-3.0 GPa). Peak broadening and almost complete amorphization were observed for Sc 2 Mo 3 O 12 at ∼8 GPa, and this was not fully reversible on decompression. At 7 GPa, the amorphization of Al 2 W 3 O 12 was not as advanced as for the molybdate and on decompression crystalline material was recovered. The compressibility of orthorhombic Sc 2 Mo 3 O 12 is highly anisotropic, but it is almost isotropic for both monoclinic Sc 2 Mo 3 O 12 and Al 2 W 3 O 12 . Both compounds show a reduction in their bulk moduli (K 0 ) at the orthorhombic to monoclinic transition: 32(2) GPa for orthorhombic and 16(1) GPa for monoclinic Sc 2 Mo 3 O 12 , and 48 GPa for orthorhombic and 28(1) GPa for monoclinic Al 2 W 3 O 12 . Sc 2 Mo 3 O 12 displays very similar high pressure behaviour to the previously studied Sc 2 W 3 O 12 .

Al2Mo3O12/polyethylene composites with reduced coefficient of thermal expansion

“…Thus far elastic constants and related properties such as bulk [55][56][57][58]. Our analysis of experimental a c versus volume filler fraction in terms of Turner's model ( Figure 6) and calculations based on the ultrasonic tests gave a bulk modulus of 13.6 ± 2.6 GPa and 13.…”

“…Our analysis of experimental a c versus volume filler fraction in terms of Turner's model ( Figure 6) and calculations based on the ultrasonic tests gave a bulk modulus of 13.6 ± 2.6 GPa and 13. [55][56][57][58]. In comparison, the bulk modulus of cubic a-ZrW 2 O 8 , the most studied thermomiotic filler, is much higher (*74 GPa) [59].…”

Structural changes accompanying negative thermal expansion in Zr2(MoO4)(PO4)2

“…Many compositions are known to form with structures related to that of orthorhombic Sc 2 W 3 O 12 [1][2][3][4]. They typically display anisotropic volume NTE while orthorhombic, but are susceptible to symmetry lowering phase transitions [5], with a concomitant loss of NTE, on cooling or modest compression [6][7][8][9]. The Sc 2 W 3 O 12 framework is amenable to a wide range of substitutions beyond the simple replacement of Sc 3+ with other trivalent ions; for example, materials such as A 2 (MO 4 )(PO 4 ) 2 (A-Zr or Hf; M-W or Mo) [10][11][12][13], (HfMg)(WO 4 ) 3 [14][15][16][17], and Zr 2 (SO 4 )(PO 4 ) 2 [18] have been reported to have related structures.…”

Pressure-induced amorphization of cubic ZrMo2O8 studied in situ by X-ray absorption spectroscopy and diffraction

“…The low densities and highly flexible frameworks of many NTE materials, combined with the presence of lattice modes that soften on volume reduction [10][11][12][13][14][15][16] predispose them to interesting highpressure behavior. Crystalline to crystalline phase transitions have been observed at high pressure in cubic ZrW 2 O 8 [11,12,[17][18][19][20], cubic HfW 2 O 8 [13,21], cubic ZrMo 2 O 8 [22,23], cubic HfMo 2 O 8 [22], ZrV 2 O 7 [24], Sc 2 W 3 O 12 [25], Sc 2 Mo 3 O 12 [26,27] and Al 2 W 3 O 12 [27][28][29]. Additionally, pressure induced amorphization (PIA) has been seen for ZrMo 2 O 8 [22,23], ZrW 2 O 8 [30], Sc 2 W 3 O 12 [31], Sc 2 Mo 3 O 12 [32] and Lu 2 W 3 O 12 [33] at low pressures.…”