Titanate Nanotube Arrays Research Articles

Structural and Magnetic Properties of Cobal Ferrite - Barium Titanate Nanotube Arrays

ABSTRACTCobalt Ferrite/Barium Titanate nanotube arrays were obtained in anodic aluminum oxide templates (AAO) of 100 nm pore diameter by a two step sol-gel process. Each phase was grown in several wetting – drying cycles starting from the cobalt ferrite layers with the barium titanate on top. As-dried composite structures were sintered at 700 C. The composite nanotubes showed a fine polycrystalline microstructure with an average grain size of 5 nm. The formation of both spinel and perovskite structures was verified by High Resolution Transmission Electron Microscopy (HR-TEM) on isolated nanotubes. The growing rate by layer was found to be lower for the BaTiO3 on top of CoFe2O4 than the later on top of the AAO. Wall sizes were estimated by Z-contrast as 9.8 nm for one layer of CoFe2O4 and 6.6 nm for six layers of BaTiO3. Magnetic properties were studied by VSM. Samples showed ferromagnetic behavior with low coercive values. By means of a finite element model the deformation and stress on the piezoelectric phase was estimated and used to simulate the magnetization reversal under stress in the composite nanotubes, using an updated micromagnetic framework to include the magnetostriction effect. Simulation results showed that a curling mode is expected with opposite vortex states at the end of the nanotubes. The change in the vortex domain structure under voltage driven applied stress is presented and discussed.

Preparation and properties of a phthalocyanine-sensitized TiO2 nanotube array for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) based on an ordered titanate nanotube (TNT) array were fabricated using phthalocyanine as a dye sensitizer. The ordered TNT photoanode was prepared via two steps: (1) electrosynthesis of the TiO2 nanotube array in the HF solution by the anodization method; (2) electrodeposition of 2,9,16,23-tetra-amino zinc phthalocyanine (TAZnPc) in the TiO2 nanotubes array. The morphological characteristics and structures of TAZnPc immobilized TiO2 NTs (TAZnPc/TiO2 NTs) were examined. The average pore diameter of the TNT structures was 100 nm and its average length was 500 nm. The diffuse reflection spectra (DRS) curves of TAZnPc/TiO2 NTs had a wide absorption at 550–950 nm, which may come from the TAZnPc. The photocurrent and photovoltage of the cells were measured with an active area of 0.25 cm2 by using CHI660B electrochemical workstation in the condition of illumination (AM 1.5, 100 mW cm−2). The open circuit voltage (Voc), short circuit current (Jsc) and fill factor (FF) of the DSSC are 0.416 V, 0.115 mA cm−2 and 0.68, respectively.

Synthesis and characterization of highly-ordered barium-strontium titanate nanotube arrays fabricated by sol—gel method

Highly uniformed barium-strontium titanate nanotube arrays were fabricated using a porous anodic aluminum oxide template from a barium-strontium titanate sol—gel solution. Electron microscope results showed that nanotubes with uniform length and diameter were obtained. The diameters and lengths of these nanotubes were dependent on the pore diameter and the thickness of the applied anodic aluminum oxide template. High resolution transmission electron microscopy and the selected-area electron diffraction pattern investigations demonstrated the perovskite structure and the polycrystalline of the fabricated barium-strontium titanate nanotubes. The characterization of the electrical and dielectric properties had also been made. Compared to thin film material, the intrinsic leakage current density is almost the same. Besides, at 30 ?C, the dielectric constant and dielectric loss of the fabricated nanotube is 80 and 0.027 at 1 MHz respectively.

Synthesis and characterization of Bi 3.15Nd 0.85Ti 3O 12 nanotube arrays

Nd-substituted bismuth titanate (Bi 3.15Nd 0.85Ti 3O 12, BNT) nanotube arrays are fabricated by means of a sol–gel method utilizing porous anodic aluminum oxide (AAO) template. The morphologies and structures have been determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The diameter and length of these nanotubes are about 200 nm and 60 μm, respectively, and their wall thickness is about 30 nm. The average grain size is around 40 nm. XRD data show that the BNT nanotubes possess bismuth-layered perovskite structure. High-resolution electron microscopy (HRTEM) image demonstrates that the BNT nanotubes are polycrystalline. Polarization–electric field ( P– E) response curves of BNT nanotube arrays were measured, and a size induced polarization reduction phenomenon is observed.

Effects of Alkalinity on the Hydrothermal Synthesis of Lead Titanate Nanotube Arrays

The alkalinity of hydrothermal solution was proved to have significant effects on the formation of lead titanate nanotube arrays. Using anodic TiO2 nanotube arrays as templates, lead titanate (PbTiO3) nanotube arrays were obtained by in situ hydrothermal synthesis in an alkali-free solution. The addition of KOH in hydrothermal solutions induced a dissolution–precipitation process, which resulted in the formation of cubic PbTiO3 particles instead of nanotubes. Compared with bulks, the nanotubular structure in PbTiO3 nanotube arrays is responsible for the differences in the Raman spectra for different specimens.

Synthesis and Growth Mechanism of Lead Titanate Nanotube Arrays by Hydrothermal Method

Lead titanate nanotube arrays were in‐situ grown by hydrothermal synthesis. The hydrothermal process is time‐dependent and in different hydrothermal reaction stages, different growth mechanisms dominate the formation of PbTiO3 nanotubes. In the initial stage in‐situ growth of PbTiO3 nanotube arrays dominates. Subsequently dissolution–precipitation process dominates and results in the deposition of PbTiO3 particles on the surface of the already‐formed PbTiO3 nanotubes. In order to in‐situ grow PbTiO3 nanotube arrays with perfect nanotubular structure, suitable hydrothermal reaction time should be applied.

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.

Hydrothermal Production of SrTiO3 Nanotube Arrays

Abstract Strontium titanate (SrTiO3) nanotube arrays were produced through a simple hydrothermal process from amorphous TiO2 nanotubes arrays. The resulting samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). During the hydrothermal treatment, the TiO2 nanotube arrays retained their shape to produce SrTiO3 nanotube arrays. The formation mechanism can be explained by the nanoscale Kirkendall effect.

Thin Films of Single-Crystalline SrTiO3 Nanorod Arrays and Their Surface Wettability Conversion

Thin films of single-crystalline SrTiO3 nanorod arrays were synthesized by ion-exchange and annealing titanate nanotube arrays. The diameter of the SrTiO3 nanorods ranged from 10 to 20 nm, and the long length axis of these nanorods was oriented in the [110] direction of the perovskite phase. These nanorod arrays were optically semitransparent and adhered well to the substrates. Due to their surface nanostructures, these nanorod surfaces exhibited superhydrophilicities with water contact angles (θ) below 3°. In addition, these surfaces turned into high-hydrophobic states (θ = 140°) when oleic acid was applied. UV illumination caused these hydrophobic thin films to become superhydrophilic states because single-crystalline SrTiO3 nanorods have strong photocatalytic oxidative activities, which decomposed the surface-adsorbed oleic acid.

Super-hydrophilic and transparent thin films of TiO2 nanotube arrays by a hydrothermal reaction

Titanate nanotube arrays were grown on sapphire substrates by sputtering deposition of titanium films and a subsequent hydrothermal treatment in an aqueous NaOH solution. Post annealing in air transformed the crystals from a titanate structure to an anatase structure. Titanate and anatase nanotube arrays were optically transparent and adhered well to the substrates. Both titanate and anatase nanotube films exhibited high-hydrophilic states with water contact angles below 5° even after dark storage for more than three months due to their surface nanostructures. UV illumination caused super-hydrophilic states with 0° water contact angles, i.e. band-gap excitations decreased the initial water contact angles in dark conditions (∼3.5°) to 0°. The hydrophilicizing rate of the anatase nanotubes was faster than that of the titanate nanotubes because the anatase nanotubes had a higher crystallinity and more absorbed photons.