Cuspidine型希土類アルミネートの高温相変態
2000 年 29 巻 1 号 p. 53-58
詳細
2000 年 29 巻 1 号 p. 53-58
Recent studies on the high-temperature martencitic phase transition of cuspidine-type rare-earth aluminates (RE4Al2O9, RE: rare-earth elements) were reviewed. Calorimetry, dilatometry, thermal gravimetry and crystal structure analyses of RE4Al2O9(RE=Y) revealed a reversible phase transformation at around 1370°C with thermal hysteresis. The cell volume of the high-temperature phase is approximately 0.4% smaller than that of the low-temperature phase. The high-tempera-ture phase crystallizes in a monoclinic cell, a space group P 21/c. This is identical to the space group of the low temperature phase. Phase transition temperatures of cuspidine-type rare-earth aluminates (RE4Al2O9, RE=Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) and gallates (RE4Ga2O9, RE=La, Pr, Nd, Sm, Eu, Gd) decreased from 1300°C (Yb) to 1044°C (Sm) for the aluminates and 1417°C (Gd) to 1271°C (La) for the gallates with increasing ionic radius of the rare-earth elements.
