Dielectric study on the phase transitions in ferroelectric (CH3NH3)2AlBr5.6H2O

1999 
The dielectric properties have been measured for single crystals of ferroelectric (CH 3 NH 3 ) 2 AlBr 5 .6H 2 O. The dielectric constant along the a direction ∈ n shows a sharp λ-type peak at the Curie temperature of 76.6 K below which the crystal shows ferroelectricity along the a direction. The dielectric constant along the a direction ∈ a obeys a Curie Weiss law with the Curie constant of 3.3×10 2 K in a temperature range about 30K above the Curie temperature, The spontaneous polarization approaches the saturation value of 6.5 × 10 -3 C/m 2 at low temperatures. Beside the ferroelectric Curie temperature, there is a first order phase transition at about 250 K where the dielectric constant shows a slight discontinuous change. The results are compared with those of the isomorphic ferroelectric crystal of (CH 3 NH 3 ) 2 AlCl 5 .6H 2 O, and discussed.
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