Polymorphism of Bi{sub 1-x}Ln{sub x}O{sub 1.5} phases (0<x<0.40) Characterization of a new compound Bi{sub 4}Ln{sub 2}O{sub 9} (x=0.33; Ln=La, Pr, Nd)
The Bi{sub 1-x}Ln{sub x}O{sub 1.5} solid solutions (Ln=La, Pr, Nd), of the {beta}{sub 2}/{beta}{sub 1}/{epsilon} (Bi-Sr-O) structural type, have been investigated in their Ln-rich domains. For Ln=La, Pr, and Nd, the upper limits are 0.35, 0.35 and 0.33, respectively. The Bi{sub 4}Ln{sub 2}O{sub 9} {epsilon} phase (x=0.33) appears to be the single definite compound. For Bi{sub 4}La{sub 2}O{sub 9}, Bi{sub 4}Pr{sub 2}O{sub 9} and Bi{sub 4}Nd{sub 2}O{sub 9}, the {epsilon}-type cells are respectively: a=9.484(4) A, b=3.982(2) A, c=7.030(3) A, {beta}=104.75(3) deg.; a=9.470(5) A, b=3.945(2) A, c=6.968(4) A, {beta}=104.73(3) deg. and a=9.439(3) A, b=3.944(2) A, c=6.923(2) A, {beta}=105.03(3) deg. . Upon heating, each monoclinic ({epsilon}) compound transforms successively into rhombohedral phases ({beta}{sub 2}/{beta}{sub 1}) and finally into a cubic fluorite-type phase. For La- and Pr-based compounds, all transitions are reversible; for Nd, depending on the thermal treatment, the reversibility of {epsilon}{yields}{beta}{sub 2} can be incomplete. These transformations are characterized using X-ray thermodiffractometry, differential thermal analysis, dilatometry and impedance spectroscopy versus temperature. Examination of Bi{sub 4}(Ln, Ln'){sub 2}O{sub 9} samples allows to correlate the evolution of the thermal behavior and of the unit cell parameters, to the lanthanide size. A partial plot of the (Bi{sub 2}O{sub 3}){sub 1-x}-(La{sub 2}O{sub 3}){sub x} phase diagram (0{<=}x{<=}0.40) is proposed.
- OSTI ID:
- 20883133
- Journal Information:
- Materials Research Bulletin, Vol. 38, Issue 1; Other Information: PII: S0025540802009844; Copyright (c) 2002 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0025-5408
- Country of Publication:
- United States
- Language:
- English
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