New high pressure rare earth tantalates RExTa2O5+1.5x (RE=La, Eu, Yb)

• Published in: Journal of solid state chemistry 2013-07, Vol.203, p.240-246
• Main Authors: Zibrov, Igor P., Filonenko, Vladimir P., Zakharov, Nikolai D., Werner, Peter, Drobot, Dmitrii V., Nikishina, Elena E., Lebedeva, Elena N.
• Format: Article
• Language: English
• Subjects: Amorphous materials; Channels; Electron microscopy; High pressure; Rare earth metals; Rare-earth tantalates; Solid state; Tantalates; Tantalum; Tantalum pentoxide; Unit cell; X-ray diffraction; X-rays
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2013.03.057

Rare earth tantalates La0.075Ta2O5.113, Eu0.089Ta2O5.134 and Yb0.051Ta2O5.077 have been prepared by solid state reaction at P=7.0GPa and T=1050–1100°C and studied by X-ray diffraction, thermal analysis and electron microscopy. Low hydrated amorphous tantalum, lanthanum, europium and ytterbium hydroxides were used as starting materials. Aqueous as well as anhydrous compounds were obtained. Title tantalates are crystallized in the structure type of F–Ta2O5 [Zibrov et al. Russ. J. Inorg. Chem. 48 (2003) 464–471] [5]. The structure was refined by the Rietveld method from X-ray powder diffractometer data: La0.075Ta2O5.113, a=10.5099(2), b=7.2679(1), c=6.9765(1)Å, V=532.90(1)Å3, Z=6, space group Ibam; Eu0.089Ta2O5.134, a=10.4182(3), b=7.2685(1), c=6.9832(1)Å, V=528.80(2)Å3, Z=6, space group Ibam; Yb0.051Ta2O5.077, a=10.4557(2), b=7.3853(1), c=6.8923(1)Å, V=532.21(1)Å3, Z=6, space group Ibam. RE atoms do not replace the tantalum in its positions but the only water in the channels of the structure. Highly charged cations RE+3 compress the unit cell so that its volume becomes less than that of F–Ta2O5. Significant decrease of the unit cell volume after water removal from the structure is possible due to the puckering of pentagonal bipyramid layers and change of the corrugation angle in the layer. The structure of RExTa2O5+1.5x and its HRTEM image (“A” arrows show empty channel, “B” arrows show filled channel). [Display omitted] •We synthesized new tantalates of RE under high pressure high temperature conditions.•RE atoms replace water molecules in the channels of the structure.•Aqueous as well as anhydrous tantalates were obtained.•Highly charged cations RE+3 compress the unit cell decreasing RE–O distances.