Phase transition of rare-earth aluminates (RE{sub 4}Al{sub 2}O{sub 9}) and rare-earth gallates (RE{sub 4}Ga{sub 2}O{sub 9})
- Tohoku Univ., Sendai (Japan). Inst. for Materials Research
Lattice parameters of RE{sub 4}Al{sub 2}O{sub 9} (RE = Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) prepared at 1,600--1,800 C and those of RE{sub 4}Ga{sub 2}O{sub 9} (RE = La, Pr, ND, Sm, Eu, and Gd) prepared at 1,400--1,600 C were refined by Rietveld analysis for the X-ray powder diffraction patterns. The parameters increased linearly with the ionic radius of the trivalent rare-earth elements (r{sub RE}). High-temperature differential calorimetry and dilatometry revealed that both RE{sub 4}Al{sub 2}O{sub 9} and RE{sub 4}Ga{sub 2}O{sub 9} have reversible phase transitions with volume shrinkages of 0.5--0.7% on heating and thermal hystereses. The transition temperatures (T{sub tr}) decreased from 1,300 C (Yb) to 1,044 C (Sm) for RE{sub 4}Al{sub 2}O{sub 9}, except for Y{sub 4}Al{sub 2}O{sub 9} (T{sub tr} = 1,377 C), and from 1,417 C (Gd) to 1,271 C (La) for RE{sub 4}Ga{sub 2}O{sub 9} with increasing ionic radius of the rare-earth elements. These transitions temperature were plotted on a curve against the ionic radius ratio of Al{sup 3+} or Gd{sup 3+} and RE{sup 3+} (r{sub Al,Ga}/r{sub RE}) except for Y{sub 4}Al{sub 2}O{sub 9}.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 116093
- Journal Information:
- Journal of the American Ceramic Society, Vol. 78, Issue 9; Other Information: PBD: Sep 1995
- Country of Publication:
- United States
- Language:
- English
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