The effect of simultaneous cation and anion substitution on the ferroelectric phase transition in (NH4)2SO4

Solid solutions of general formula (NH4)2—xAx(SO4)y(BX4)1—y (A = K+, Rb+ and TI+, BX4 = SeO4 and BeF4) were studied. In all cases the degree of substitution in (NH4)2SO4 was established. The simultaneous partial substitution of ammonium cation and sulfate anion in (NH4)2SO4, with the same spatial groups (Pnam-Pna21) produces changes in the phase transition temperature and in ΔH and ΔS. The new cation-anion bonds may explain the greater energy involved in the phase transition. Using thermal measurements and X-ray diffraction at low temperature, we can conclude that both cations and anions produce a cooperative effect in the mechanism of the phase transition in these new compounds.

Keywords:

• Keywords
• Ammonium sulfate
• phase transitions
• ferroelectric
• solid solutions