IMF2017

Rb₂ZnI₄ is a crystal having monoclinic structure with P2₁/m at room temperature. On cooling, it undergoes a phase transition to an incommensurate phase below 62 K [1], where the b-axis dielectric constant ε_b forms a λ-type peak. On further cooling, ε_b again increases and forms a broad peak at around 5 K, however, it shows no ferroelectricity at any temperatures. To elucidate such properties, we performed dielectric measurements for Rb₂ZnI₄ and mixed systems such as (Rb_1-xK_x)₂ZnI₄ and Rb₂Zn_1-xCd_xI₄ and revealed that the system shows a ferroelectric transition of the first order for x > 0.13 ~ 0.14, and with increase of x, ferroelectric Curie point moves high temperature [2-4]. On the other hand, Mashiyama [5] theoretically derived a phase diagram which reproduces an aspect of our results. In this presentation, we shall report the latest data of thermal expansion measurements for both (Rb_1-xK_x)₂ZnI₄ and Rb₂Zn_1-xCd_xI₄.

References

[1] J. Puragahn: Doctor Thesis, Karlsruhe University (1998).

[2] M. Takashige et al: J. Phys. Soc. Jpn. 81, 045001-2 (2012).

[3] T. Yamaguchi et al: Ferroelectrics 462, 104-109 (2014).

[4] R. Shibata et al: J. Korean Phys. Soc. 66, 1367-1370 (2015).

[5] H. Mashiyama: J. Phys. Soc. Jpn. 84, 104712 (2015).