Large electrocaloric effects in single-crystal ammonium sulfate

Area of Science:

• Materials Science
• Thermodynamics
• Solid State Physics

Background:

• Electrocaloric (EC) effects, the change in temperature of a dielectric material upon application or removal of an electric field, are typically observed near phase transitions.
• Research has primarily focused on ceramic and polymer materials for EC applications.

Purpose of the Study:

• To investigate the electrocaloric effects in an inorganic salt, ammonium sulfate ((NH4)2SO4).
• To determine the potential of ammonium sulfate for novel cooling applications by quantifying its EC properties near its order-disorder transition.

Main Methods:

• Utilized a single crystal of ammonium sulfate, thinned to 50 μm.
• Applied a Maxwell relation to calculate the isothermal entropy change.
• Employed the Clausius-Clapeyron equation to determine the adiabatic temperature change.

Main Results:

• Observed a large isothermal entropy change of 30 J K⁻¹ kg⁻¹ for a field change of 400 kV cm⁻¹.
• Calculated a corresponding adiabatic temperature change of 4.5 K.
• Identified the order-disorder transition onset at 223 K on cooling.

Conclusions:

• Ammonium sulfate exhibits significant electrocaloric effects, particularly near its order-disorder transition.
• The findings suggest that inorganic salts like ammonium sulfate are promising candidates for developing advanced EC cooling materials.
• This study expands the scope of materials investigated for EC applications beyond traditional ceramics and polymers.