Caifu Zhong

Room temperature multiferroic behavior of Cr-doped ZnO films

Single-phase 9 at. % Cr-doped ZnO film has been prepared on Pt(111)/Ti/SiO2/Si(100) substrates by reactive sputtering method. The film is found to present ferroelectric and ferromagnetic behaviors simultaneously at room temperature, and it undergoes transitions to paraelectric and paramagnetic phases at ∼368–373 and ∼495 K, respectively. It is considered that the local electric dipoles induced by the distortions of CrO4 tetrahedra should be responsible for the ferroelectricity. On the other hand, the ferromagnetic ordering could be explained by the interaction of the localized spins with statically occupied polaron states. The multiferroic behavior adds a dimension to the multifunction of ZnO.

Bulk dense fine-grain (1−x)BiScO3–xPbTiO3 ceramics with high piezoelectric coefficient

High density fine grain (1−x)BiScO3–xPbTiO3 ceramics were successfully prepared by two-step sintering and their ferroelectric properties were investigated. Experimental evidence indicates the existence of a morphotropic phase boundary at the composition x=0.635, which exhibits a piezoelectric coefficient d33 of 700 pC/N at room temperature, significantly higher than the reported values to date. Furthermore, a higher electromechanical coupling factor Kp=0.632 and a larger remnant polarization Pr=47.3 μC/cm2 were obtained. The paraelectric-to-ferroelectric phase transition occurs at 446 °C, slightly lower than in the coarse grain ceramics with a similar composition, suggesting a grain size effect. The local effective piezoelectric coefficient d33∗ was estimated to be 795 pC/N at 2.29 V, measured by scanning probe microscopy. Further atomic force microscope observation revealed the existence of 90° domains of about 60–70 nm in width, confirming the previous results that small domain structure enhances the pi...

Ferroelectric PbTiO3 nanotube arrays synthesized by hydrothermal method

Lead titanate nanotube arrays with perfect nanotubular structure and excellent piezoelectric property were formed by hydrothermal method. The nanotubular structure proved to have strong influences on both Curie temperature and piezoelectric properties of PbTiO3 nanotube arrays. The Curie temperature of PbTiO3 nanotube arrays was detected to be 620°C. Perfect piezoelectric properties with a maximum displacement of 0.88nm and d33* of 120pmV−1 were observed in PbTiO3 nanotube arrays.

Epitaxial growth of sol-gel derived BiScO3-PbTiO3 thin film on Nb-doped SrTiO3 single crystal substrate

BiScO3–PbTiO3 (BSPT) thin film was grown on electrical conductive Nb-doped SrTiO3 (100) (Nb-STO) single crystal substrate by a sol-gel method. The x-ray diffraction and high resolution transmission electron microscopy proved the epitaxial growth relation between the BSPT thin film and Nb-STO substrate. The [001]-epitaxial BSPT thin film exhibited considerable high remanent polarization of 74μC∕cm2 and effective piezoelectric coefficient d33* of 130pm∕V, which were much higher than those of the (100)-oriented BSPT thin film grown on traditional silicon substrate.

Fabrication and properties of epitaxial growth BiScO3–PbTiO3 thin film via a hydrothermal method

BiScO3–PbTiO3 thin film was hydrothermally deposited on Nb-doped SrTiO3 [100] single crystal substrate at 180°C with a large thickness of 3.1μm. The x-ray diffraction and high resolution transmission electron microscopy confirmed the epitaxial growth relationship between the BSPT thin film and Nb-STO substrate. Single-crystal-like polarization hysteresis loops were observed, with the remanent polarization of 30μC∕cm2. Piezoelectric force microscopy revealed a single +c domain structure of the film, while exceptional linear piezoelectric response was observed with the effective piezoelectric constant d33* of 65pm∕V. The temperature dependence of the effective d33* indicated that this film exhibited a high temperature stability.

Synthesis and photoluminescence of CdS QDs in ZrO2 nanotubes by sequential chemical bath deposition

Highly ordered ZrO2 nanotube (NT) arrays were fabricated by anodization in organic electrolyte containing NH4F. A facile sequential-chemical bath deposition technique was used to prepare CdS quantum dots (QDs) in the pores of ZrO2 NTs. XRD and HRTEM results confirmed the formation of single-phase wurtzite CdS nanoparticles with uniform size around 10 nm. UV–vis absorption and photoluminescence spectra proved that the CdS QD coating strongly enhanced the photon absorption of the NT arrays, as well as their PL signals in the visible broadband section which mostly arose from structure-dependent defects and oxygen vacancies in the nanohybrid layers.

Template-based synthesis and magnetic properties of Mn-Zn ferrite nanotube and nanowire arrays

Template-based electrophoretic deposition of Mn-Zn ferrite nanotubes (NTs) and nanowires (NWs) were achieved using anodic alumina oxide (AAO) membranes. The effect of electrophoretic current and deposition time on the morphology of the tubes was investigated. The samples show cubic spinel structure with no preferred orientation. Room-temperature magnetic properties of the Mn-Zn ferrite NT/NW arrays were studied. The magnetic easy axis parallels the NT/NW’s channel axis attributing to the large shape anisotropy in this direction, especially for the NTs with a small wall thickness. Magnetocrystalline anisotropy and magnetostatic interactions were found dominant in the samples when applied field was perpendicular to the channel axis.