Bilayered Pb(Zr(1–x),Tix)O3 ferroelectric thin film heterostructures show complex ferroelastic nanodomain patterns. These ferroelastic nanodomains exist only in the upper layer, and hence are able to move under the application of an external electric field. Quantitative analysis reveals an enhanced piezoelectric coefficient of ≈220 pm V−1, rendering them attractive for a variety of electromechanical devices.

There is tremendous fl urry of research interest in multiferroic materials that exhibit multiple primary ferroic order parameters simultaneously and that have practical applications. [ 1 ] Much of the recent work on multiferroic materials was directed towards bringing ferroelectricity and ferromagnetism together in a single-phase compound. [ 2 ] The search for these materials is driven by the prospect of controlling charges by applying magnetic fi elds or/and manipulating spins by applying electrical fi eld and using this to construct new paradigms of spintronics devices and data storage applications. [ 1 ] Despite these intriguing characteristics, the simultaneous presence of electric and magnetic dipoles does not guarantee mutual coupling because the microscopic mechanisms of ferroelectricity and ferromagnetism are quite different. [ 2 ] Owing to these fundamental and technological challenges, the long sought after single-phase multiferroic material was hampered and was mainly based on silicon incompatible perovskite materials, [ 1 ] which limits their multifunctional applications.Zinc oxide (ZnO) has been of growing technological importance due to its versatile properties. [ 3 ] The substitution of transition-metal ions into the Zn sites leads to ferromagnetic ordering. [ 4 ] Additionally, doped-ZnO bulk crystals and thin fi lms could exhibit ferroelectric behavior. [ 5 ] Recently, a number of reports have shown the coexistence of ferromagnetism and ferroelectricity in doped ZnO. [ 6 ] However, there are no reports on the demonstration of mutual manipulation between ferromagnetism and ferroelectricity in this class of material. Despite these exciting characteristics, the demonstration of mutual ferromagnetic and ferroelectric coupling (true multiferroic behavior) in doped-ZnO fi lms poses a technology diffi culty because 1) ZnO is not suffi ciently insulating, which undermines the ferroelectric measurement and 2) most of the ferromagnetic and ferroelectric order in doped-ZnO fi lms are mutually exclusive. [ 2 ] Here, we report the mutual manipulation of ferromagneticferroelectric properties in a copper-doped ZnO (ZnO:Cu) fi lm and demonstrate domain structure manipulation in this material. The ZnO:Cu is a particular interesting system for several reasons. First, the fact that neither metallic Cu nor its oxides are ferromagnetic at 300 K is advantageous, removing any possibility of ferromagnetism arising from the presence of precipitates or secondary phases. The ZnO:Cu was reported to possess ferromagnetism, attributing to the presence of oxygen vacancies and Cu ions. [ 7 , 8 , 9 ] Second, Cu atoms in ZnO are well-known as electron traps, which results in a high resistivity fi lm. [ 10 ] A highly resistive fi lm reduces the current leakage, favoring ferroelectric measurement. In this study, we discover a striking multiferroic phenomenon in ZnO:Cu that is attributed to the interplay of Cu ions and oxygen vacancies (V o ). The substitution of Cu 2 + into Zn 2 + sites gives rise to ferroelectricity, while Cu 2 + ...

Vertically aligned, single crystalline ZnO nanorods with a high packing density and diameter of B60 nm have been successfully synthesized via a low-temperature hydrothermal route on glass substrates pre-deposited with a ZnO seeding layer. The seeding layer exhibits an epitaxial effect on the growth and alignment of the ZnO nanorods. This epitaxial effect can arise from two considerations, namely the crystalline orientation and surface roughness of the seeding layer, which can be controlled by the curing temperature. The ZnO seeding layer that was cured at 3501C exhibited a preferred (0002) crystalline orientation of wurtzite hexagonal structure and a low surface roughness. It was demonstrated to promote the vertical growth of ZnO nanorods. The ZnO nanorods grew in an almost linear relationship with hydrothermal time up to 8 h, but thereafter started to dissolve as the reaction time extended beyond 8 h, due to competition from the homogeneous nucleation of ZnO microparticles in the solution.

High-performance piezoelectric devices based on ferroelectric materials rely heavily on ferroelastic domain wall switching. Here we present visual evidence for the local mechanisms that underpin domain wall dynamics in ferroelastic nanodomains. State-of-the-art band excitation switching spectroscopy piezoforce microscopy (PFM) reveals distinct origins for the reversible and irreversible components of ferroelastic domain motion. Extrapolating the PFM images to case for uniform fields, we posit that, while reversible switching is essentially a linear motion of the ferroelastic domains, irreversible switching takes place via domain wall twists. Critically, real-time images of in situ domain dynamics under an external bias reveal that the reversible component leads to reduced coercive voltages. Finally, we show that junctions representing three-domain architecture represent facile interfaces for ferroelastic domain switching, and are likely responsible for irreversible processes in the uniform fields. The results presented here thus provide (hitherto missing) fundamental insight into the correlations between the physical mechanisms that govern ferroelastic domain behavior and the observed functional response in domain-engineered thin film ferroelectric devices.

Heterolayered Pb(Zr1−xTix)O3 thin films consisting of different numbers of alternating Pb(Zr0.7Ti0.3)O3 and Pb(Zr0.3Ti0.7)O3 layers are studied. They exhibit (001)∕(100) preferred orientation and dense microstructure when baked at 500°C and then thermally annealed at 650°C. They demonstrate a considerably low leakage current density in the order of 10−7A∕cm2. Their ferroelectric and dielectric properties are improved with increasing number of alternating Pb(Zr0.7Ti0.3)O3 and Pb(Zr0.3Ti0.7)O3 layers, thereby the six-heterolayered PZT thin film shows a much enhanced remanent polarization of 41.3μC∕cm2 and relative permittivity of 710 at 1kHz. In fatigue test, a wake-up phenomenon is observed with the heterolayered films, where the degradation in switchable polarization is delayed. At elevated temperatures, the wake-up phenomenon was reduced, leading to fatigue degradation at a relatively lower number of switching cycles. The phenomenon is related to the injected electron causing oxygen vacancies, the accumulation of which impedes the domain switching.