BaWO₄-II (a high-pressure form)

Abstract

Abstract. Monoclinic, P21/n, a = 13.159 (12), b = 7.161 (3), c=7.499 (6) A, /?=93.76 (5) °. Z=8. Om=7"17, Dx= 7"26 g cm -3. Crystals were synthesized under high pressure at high temperature. The structure has no direct resemblance either to the scheelite-or to the wolframitetype. It consists of densely packed layers of WO6 octahedra, which are connected by edge-and corner-sharing; barium atoms are located between them. The coordination number of the barium atoms has increased in comparison with the structure under ordinary conditions.Introduction. This phase exists above the pressure P(kbar) = 26.7 + 0.0265 T (°C), (T= 600-1000 °C), and is quenchable to normal pressure (Fujita, Yamaoka & Fukunaga, 1974).The intensity data were collected on a Rigaku fourcircle diffractometer with Mo Kez (2=0.70926 A,) radiation monochromatized by graphite. In the range 20 < 90°, 6099 independent reflexions were measured, of which 3791 were considered not observed. The systematic absences were h0/, h + l= 2n + 1, and 0k0, k =

High pressure X-ray diffraction study on BaWO4-II

“…• C [4,5]. Later, the monoclinic BaWO 4 -II has also been obtained at about 10 GPa and room temperature [6,7].…”

“…88, Z = 4) plays a significant role in mineralogy, materials science, and geoscience. Under ambient conditions, a large number of ABO 4 -type tungstates and molybdates crystallize in this structure [1]. Many other ABO 4 compounds with zircon (I4 1 /amd), monazite (P2 1 /n), and CrVO 4 -type structures (Cmcm) transform to the scheelite polymorph at high pressure [2].…”

“…Many other ABO 4 compounds with zircon (I4 1 /amd), monazite (P2 1 /n), and CrVO 4 -type structures (Cmcm) transform to the scheelite polymorph at high pressure [2]. The pressure effects on the structural and electronic properties of scheelite-type ABO 4 crystals have attracted wide interest of researchers, and a pressure-induced structural sequence scheelite → fergusonite → P2 1 /n → BaMnF 4 → Cmca has been explored [3]. BaWO 4 -II (SG: P2 1 /n, No.…”

Raspite from Broken Hill

“…At higher pressure, new phases were found in PbWO4 (Chang, 1971) and BaWO 4 (Fujita, Yamaoka & Fukunaga, 1974). The high-pressure form of BaWO 4 (BaWO4-II) has a characteristic dense structure (Kawada, Kato & Fujita, 1974), and that of PbWO 4 is * A list of structure factors has been deposited with the British Library Lending Division as Supplementary Publication No. SUP 32000 (11 pp.).…”

PbWO4-III (a high-pressure form)

“…Since the cell dimensions and space group indicated that PbWO4-11I is probably isomorphous with the high-pressure phase BaWO4-1I (Kawada, Kato & Fujita, 1974), the fractional coordinates found there were used as the starting point for full-matrix leastsquares refinement. The temperature factors of the O atoms were refined isotropically.…”