Dielectric Study on the Phase Transitions in RbMgBr₃ and Cs₂MgCl₄

Abstract

Single crystals of RbMgBr₃ and Cs₂MgBr₄ were prepared, and phase transitions have been studied by dielectric measurements. Three phase transitions were found in RbMgBr₃ at 226 K, 238 K, and 456 K. The phase between 226 K and 238 K (phase III) becomes narrower with increasing hydrostatic pressure and disappears at about 800 MPa. The dielectric anomalies at the phase transitions and the pressure-temperature phase diagram are quite similar to those KNiCl₃-family ferroelectrics. This would imply that phase III of RbMgBr₃ is ferroelectric. Phase transitions accompanied with rather small dielectric anomalies are found in Cs₂MgBr₄ at 51 K, 84 K, and 123 K. Ferroelectric hysteresis loop has not been observed for Cs₂MgBr₄ along any of the crystallographic axes.

Keywords:

• Phase transition
• dielectric
• RbMgBr₃
• Cs₂MgBr₄
• pressure effect