Ferroelastic Phase Transition in K3H(SeO4)2
1982 年 51 巻 5 号 p. 1461-1468
詳細
1982 年 51 巻 5 号 p. 1461-1468
Optical observation of twin structures, the measurement of lattice deformation and X-ray examinations of K3H(SeO4)2 were carried out in a temperature range between 25°C and 130°C. It was found that K3H(SeO4)2 undergoes the improper ferroelastic phase transition at 117°C (Tc) and has spontaneous strains e13=−5.1×10−3 and (e22−e11)⁄2=4.8×10−3 at room temperature. The crystal is monoclinic with the space group A2/a below Tc and trigonal with the space group R\bar3m above Tc. It was clarified by both observation and symmetry consideration that K3H(SeO4)2 below Tc indicates two types of domain boundaries and three kinds of orientations (or domains) which appear as a result of the phase transition. It is suggested that the phase transition may be caused by a soft mode with k=(1⁄2)g2.
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