Time-dependent change of ferroelectric, dielectric and piezoelectric properties (so-called aging phenomena) is well observed in ferroelectrics and is an important issue both in physics and in applications. However, this issue has remained controversial for many decades without a clear microscopic explanation. Recently PhD candidate Zhang Lixue (advisor: Prof. Ren Xiaobing) has solved this long-standing puzzle; she provides a unified explanation for all ferroelectric aging effects. This work will soon appear in Physical Review B.

Zhang Lixue devised a critical experiment: she made a "single-domain" Mn-doped BaTiO3 single crystal and studied its aging effect. The result of this important experiment excludes the long-believed mysterious "domain-wall-pinning effect" as the primary origin of aging, and strongly suggests that volume effect is the governing mechanism for ferroelectric aging. Most importantly, she shows that the volume effect actually comes from a universal symmetry-conforming principle of point defects (proposed by Prof. Ren), which stabilizes existing domain configuration and thus induces aging effect. With this clear microscopic mechanism, she is able to explain all known ferroelectric aging effect, including not only the aging in large signal properties (hysteresis loop), but also the small signal aging of dielectric and piezoelectric constant. This study thus suggests there exists a unified microscopic explanation for all ferroelectric aging.