Proton Ordering Induces a Polar Structure in the Antiferromagnetic Solid Proton Conductor FeH₆(PO₄)₃

Area of Science:

• Solid-state chemistry
• Materials science
• Condensed matter physics

Background:

• Magnetoelectric materials are crucial for advanced applications, combining ferroelectric and magnetic properties.
• Proton conductors are vital for energy technologies, but often lack other functional properties.

Purpose of the Study:

• To investigate FeH6(PO4)3 for coexisting proton conductivity, magnetic, and polar properties.
• To explore its potential as a novel magnetoelectric material.

Main Methods:

• Neutron diffraction and second harmonic generation experiments to determine crystal structure.
• Magnetic measurements and theoretical calculations to characterize magnetic and polar behavior.

Main Results:

• FeH6(PO4)3 crystallizes in the polar R3c space group, exhibiting proton conductivity.
• Demonstrated coexistence of polar structural features (net polarization ~10 μC cm-2) and antiferromagnetism below 28 K.
• Identified polar proton ordering and Fe3+ octahedral arrangement as key factors.

Conclusions:

• FeH6(PO4)3 presents a unique combination of proton conductivity, ferroelectricity, and antiferromagnetism.
• This material is a promising candidate for magnetoelectric applications within the solid ionic conductor phase space.
• Encourages further research into multifunctional solid ionic conductors.