  There are two silver perovskite oxides: AgNbO3 and AgTaO3. AgNbO3 has a
noncentrosymmetric group of Pmc21 at room temperature with a ferri-electric
ordering of polarization. Such a ferri-electric state with small polarization
can be changed into a ferroelectric state with very large polarization by a
high electric field or by a chemical modification. The induced ferroelectric
phase shows promising electromechanical response for applications in
piezoelectric devices. In contrast, AgTaO3 is a quantum paraelectric, but
ferroelectricity also can be induced through chemical substitution. The
findings of good ferroelectric and piezoelectric performance in the silver
perovskites are hoped to trigger further theoretical and experimental
investigations on these systems.
