The secondary ferroelectricity along the c-direction of Rb₂CoCl₄

Abstract

The most ferroelectrics of the Rb₂ZnCl₄ group exhibit ferroelectricity in the a-direction. It was reported that the Rb₂ZnCl₄ indicates ferroelectricity also in the pseudo-hexagonal c-direction and the Rb₂ZnBr₄ and Rb₂CoBr₄ show not only antiferroelectricity along the b-direction in the intermediate phase but also ferroelectricity along the c-direction below the second Curie point. In this work, by means of a pyroelectric charge measurement, it was found that Rb₂CoCl₄ crystals exhibit the secondary ferroelectricity below the second Curie transition point, T _C2 = 69·0 K along the pseudo-hexagonal c-direction. The temperature dependence of the spontaneous polarization in the a- and c-direction, P _a ^F, and P_c ^F, was measured down to 4 K. Furthermore the temperature dependence of the dielectric constants along the three crystallographic axes was reexamined between 4 K and about 350 K. A small peak anomaly of the dielectric constant in the a-direction was observed around 20 K.

Key Words:

• Keywords
• Rb₂CoCl₄
• Rb₂ZnCl₄ group ferroelectrics
• ferroelectricity
• the secondary ferroelectricity
• pyroelectricity
• Rb₂CoBr₄
• Rb₂ZnBr₄