Formation of new compounds Ln{sub 4}Al{sub 2}O{sub 9} in the Ln{sub 2}O{sub 3}{center_dot}Al{sub 2}O{sub 3} system (Ln = La, Pr, Tb)
- Haldor Topsoee A/S, Lyngby (Denmark). Research Labs.
The new compounds La{sub 4}Al{sub 2}O{sub 9}, Pr{sub 4}Al{sub 2}O{sub 9}, and Tb{sub 4}Al{sub 2}O{sub 9} were identified in the system 2Ln{sub 2}O{sub 3}{center_dot}Al{sub 2}O{sub 3}. X-ray powder diffraction showed that they were isomorphous with the previously characterized Ln{sub 4}Al{sub 2}O{sub 9} (Ln = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Y) and Ln{sub 4}Ga{sub 2}O{sub 9} (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd). La{sub 4}Al{sub 2}O{sub 9}: P2{sub 1}/c, a = 7.97 {angstrom}, b = 11.09 {angstrom}, c = 11.41 {angstrom}, {beta} = 108.8{degree}, Z = 4; Pr{sub 4}Al{sub 2}O{sub 9}: P2{sub 1}/c, a = 7.80 {angstrom}, b = 11.03 {angstrom}, c = 11.31 {angstrom}, {beta} = 109.6, Z = 4; and Tb{sub 4}Al{sub 2}O{sub 9}: P2{sub 1}/c, a = 7.40 {angstrom}, b = 10.58 {angstrom}, c = 11.16 {angstrom}, {beta} = 107.2{degree}, Z = 4. The lanthanum and praseodymium compounds were metastable phases in the Ln{sub 4}Al{sub 2}O{sub 9} systems and transformed into LaAlO{sub 3} and La{sub 2}O{sub 3}, and PrAlO{sub 3} and PrO{sub 1.83} upon prolonged heating at 1,200 C, respectively. Ln{sub 4}Al{sub 2}O{sub 9} (Ln = La,Pr) were synthesized by precipitation of Al(OH){sub 4}{sup {minus}} with Ln{sup 3+} (aq) and subsequent heating at 900 C for 10 h. Tb{sub 4}Al{sub 2}O{sub 9} required calcination at 1,200 C for 10 h. The formation of La{sub 4}Al{sub 2}O{sub 9} and Pr{sub 4}Al{sub 2}O{sub 9} was followed by TGA-DSC, which was also used to assess their thermal stability. Several other members of the above family of compounds were similarly synthesized by the new synthesis route. Particularly, for Nd{sub 4}Al{sub 2}O{sub 9} this represented a significantly improved method.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 417783
- Journal Information:
- Journal of the American Ceramic Society, Vol. 79, Issue 11; Other Information: PBD: Nov 1996
- Country of Publication:
- United States
- Language:
- English
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