Sol-gel-derived PbTiO3

The sol-gel process is a technique which is applicable for forming ceramic materials. In this process, liquid precursor materials are reacted to form a sol which then polymerizes into an inorganic polymeric gel. Advantages of this process over standard powder preparation of ceramics are: purity, homogeneity, control of macro- and micro-structures, and low processing temperatures. In our laboratory the sol-gel process has been used to form lead titanate. We detail a procedure which has produced dried monolithic gels up to 1.5 cm in diameter. The as-dried gels have not been exposed to temperatures above 40 C and are X-ray amorphous. Samples of the gels were crushed into powder and heated at 8 C min^–1 to various temperatures up to 500 C, held for a variety of times, and then cooled to room temperature. After certain annealing procedures crystalline phases were observed. The initial crystalline phase to emerge has not yet been identified. Upon further annealing this phase transforms to tetragonal PbTiO₃.     

Sol-gel derived PbTiO3

Lead titanate gels have been prepared by adding an aqueous nitric acid solution to a Pb-Ti complex alkoxide. A systematic study was made to examine the effects of process parameters such as amounts of water and acid alkoxide molarity on the gelation time as well as on the structure of the gels obtained. The gel structure was characterized by the elastic modulus which was determined via sound wave propagation through the gels. It was found that an increase in both the amount of water and alkoxide molarity caused rapid gelation. Acid additions not only suppressed gelation but also reduced the elastic moduli of the resultant gels. Gels having a low elastic modulus were found to be desirable for the suppression of cracking during ageing and drying. Addition of an excessive amount of acid, however, prevented the formation of a large scale polymer-network and resulted in a powder-like gel. The porosity and dielectric constant of dried gels are also reported.     

Hierarchical nanostructures of ZnO obtained by spray pyrolysis

A two step spray pyrolysis deposition method was applied in order to grow ZnO nanorod core/ZnO shell hierarchical nanostructures with various surface morphologies, such as a highly organised platelet network on the side facets of the ZnO rod and bundles of nanoneedles on the top plane of the rod. First, well-shaped ZnO nanorods with lengths of ca. 1 μm and average diameters of 150–300 nm were deposited from zinc chloride (ZnCl₂·2H₂O) aqueous solutions onto TCO/glass substrates. Then, zinc acetate (Zn(CH₃COO)₂·2H₂O) solution was pulverised over the surface of the sprayed ZnO nanorods at a growth temperature of approximately 330 °C within 6–10 min. The obtained structures were characterised by high resolution SEM, UV–VIS and XRD. To estimate the surface areas and photocatalytic ability of the bare rods and hierarchical structures, their adsorption ability and activity of photocatalytic oxidation of doxycycline were measured. It was found that the surface area of hierarchical structures comprised of a network of platelets is at least 4 times larger than that of a bare rod. The structural and morphological properties of sprayed hierarchical structures largely depend on the spraying rate of the zinc acetate solution and on the ZnO nanorod top plane shape.     

New roots to formation of nanostructures on glass surface through anodic oxidation of sputtered aluminum

New processes for the preparation of nanostructure on glass surfaces have been developed through anodic oxidation of sputtered aluminum. Aluminum thin film sputtered on a tin doped indium oxide (ITO) thin film on a glass surface was converted into alumina by anodic oxidation. The anodic alumina gave nanometer size pore array standing vertically on the glass surface. Kinds of acids used in the anodic oxidation changed the pore size drastically. The employment of phosphoric acid solution gave several tens nanometer size pores. Oxalic acid cases produced a few tens nanometer size pores and sulfuric acid solution provided a few nanometer size pores. The number of pores in a unit area could be changed with varying the applied voltage in the anodization and the pore sizes could be increased by phosphoric acid etching. The specimen consisting of a glass substrate with the alumina nanostructures on the surface could transmit UV and visible light. An etched specimen was dipped in a TiO₂ sol solution, resulting in the impregnation of TiO₂ sol into the pores of alumina layer. The TiO₂ sol was heated at ~400 °C for 2 h, converting into anatase phase TiO₂. The specimens possessing TiO₂ film on the pore wall were transparent to the light in UV–Visible region. The electro deposition technique was applied to the introduction of Ni metal into pores, giving Ni nanorod array on theglass surface. The removal of the barrier layer alumina at the bottom of the pores was necessary to attain smooth electro deposition of Ni. The photo catalytic function of the specimens possessing TiO₂ nanotube array was investigatedin the decomposition of acetaldehyde gas under the irradiation of UV light, showing that the rate of the decomposition was quite large.     

New roots to formation of nanostructures on glass surface through anodic oxidation of sputtered aluminum

New processes for the preparation of nanostructure on glass surfaces have been developed through anodic oxidation of sputtered aluminum. Aluminum thin film sputtered on a tin doped indium oxide (ITO) thin film on a glass surface was converted into alumina by anodic oxidation. The anodic alumina gave nanometer size pore array standing vertically on the glass surface. Kinds of acids used in the anodic oxidation changed the pore size drastically. The employment of phosphoric acid solution gave several tens nanometer size pores. Oxalic acid cases produced a few tens nanometer size pores and sulfuric acid solution provided a few nanometer size pores. The number of pores in a unit area could be changed with varying the applied voltage in the anodization and the pore sizes could be increased by phosphoric acid etching. The specimen consisting of a glass substrate with the alumina nanostructures on the surface could transmit UV and visible light. An etched specimen was dipped in a TiO₂ sol solution, resulting in the impregnation of TiO₂ sol into the pores of alumina layer. The TiO₂ sol was heated at ∼400 °C for 2 h, converting into anatase phase TiO₂. The specimens possessing TiO₂ film on the pore wall were transparent to the light in UV–Visible region. The electro deposition technique was applied to the introduction of Ni metal into pores, giving Ni nanorod array on the glass surface. The removal of the barrier layer alumina at the bottom of the pores was necessary to attain smooth electro deposition of Ni. The photo catalytic function of the specimens possessing TiO₂ nanotube array was investigated in the decomposition of acetaldehyde gas under the irradiation of UV light, showing that the rate of the decomposition was quite large.     

Crystal clamping in PbTiO3 glass-ceramics

Lead titanate crystals precipitated in borate glasses by the glass-ceramic process have been found by X-ray diffraction to have abnormally low axial ratios. This has been shown to be due primarily to the stress applied by the surrounding glass matrix.     

Crystallization of nanometre-size coprecipitated PbTiO3 powders

Crystallization of coprecipitated PbTiO₃ powder was studied by calcining as-precipitated powders at 400–800 °C for up to 262 h. The coprecipitated powders were prepared from a solution containing a 1∶1 molar ratio of Pb(NO₃)₂∶TiCl₄ and a 1.1∶1 molar ratio of H₂O₂∶TiCl₄. The solution containing the lead and titanium complexes was slowly added to NH₄OH solution under constant pH (10.00±0.05) conditions that induced precipitation. Transmission electron microscopy and X-ray diffraction indicated that the calcined powders consisted of an intimate mixture of amorphous, cubic (or distorted tetragonal withc ₀/a ₀<1.01), and tetragonal (c ₀/a ₀=1.065) PbTiO₃ particles between 10 and 400 nm, with both particle size and phase content depending on heat treatment. Powders exhibiting the cubic or distorted tetragonal phase consisted of particles between 20 and 200 nm in diameter. Fully crystalline tetragonal PbTiO₃ powders consisting of 100–400 nm particles were prepared.     

PbTiO3纳米晶的制备及表征

以硬脂酸、乙酸铅和钛酸丁酯为原料用硬脂酸凝胶法合成ＰｂＴｉＯ３纳米晶原粉，利用改进的烧结设备，同时采用Ｎ２气氛下预烧，通过调节Ｎ２和Ｏ２的流量控制烧结气氛，得到粒径重复性好的ＰｂＴｉＯ３纳米晶，用差热分析，热重分析和Ｘ－射线衍射对合成过程进行了研究，用透射电镜考查纳米晶的粒度和形貌，用５ＤＸ－红外光谱仪对ＰｂＴｉＯ３纳米晶的红外透射谱进行了测试分析。     

Phase transformations in sol-gel prepared PbTiO3

The sol-gel preparation of PbTiO₃ by two different methods is reported. Both methods began with titanium isopropoxide and lead acetate as organic precursors, but without or with hydrochloric acid as catalyst, respectively. Preparation procedures and working atmosphere also differred. The crystallization by thermal treatments and laser annealing was followed by XRD and Raman spectroscopy. When no hydrochloric acid was used, an intermediate pyrochlore phase, Pb₂Ti₂O₆, was observed during the thermal treatment, and the final perovskite was obtained together with PbTi₃O₇ as the minor phase. Using the catalyst, the pure perovskite, PbTiO₃, was obtained through an unidentified phase appearing at the beginning of the crystallization process. Frequency changes in the Raman spectra during the crystallization are attributed to pressure effects on the microcrystals.     

Negative-Pressure-Induced Large Polarization in Nanosized PbTiO3

Ferroelectric materials usually undergo decay with particle size decreasing into the nanoscale. At the critical value, the crystal structure undergoes a transition from the ferroelectric to paraelectric phase and the ferroelectricity vanishes. It is a big issue to sufficiently maintain strong ferroelectricity at the nanoscale. Herein, it is reported that synthesized 0D freestanding PbTiO₃ nanoparticles (NPs) present negative pressure along the c axis (Δc/c_bulk × 100% = −2.406), inducing large spontaneous polarization P_S (71.2 µC cm⁻² in 12 nm). Further local structural studies by atomic pair distribution functions and extended X-ray absorption fine structure indicate the structural evolution of nanosized PbTiO₃. High-angle annular dark-field STEM images reveal the existence of preponderant PbO-terminations on the surface of the PbTiO₃ NPs. Ab initio calculation reveals the enhanced hybridization between Pb and O ions, which gives rise to the negative pressure and tensile stress to stabilize the high tetragonality and large polarization. The present work demonstrates an untraditional route to enhance the ferroelectricity and related properties in functional nanostructured materials, being of significance to nanodevices.     

纳米晶钛酸铅的合成及其介电性能的研究

采用硬脂酸凝胶法(SAG)制各了纳米晶PbTiO3，用差热—热重分析、红外光谱分析、X光衍射分析及透射电镜等手段对产物的形成过程、晶型、粒径进行了表征。通过对材料介电性能的研究发现，纳米晶钛酸铅在接近静态条件下的低频介电常数远大于常规材料的介电常数，随着粒径的减小，纳米晶钛酸铅的低频介电常数逐渐增大。     

Synthesis and characterization of nm-sized PbTiO3 crystallites

In this work attempt is made to synthesize PbTiO₃(PT) nanopowder by low temperature direct synthesis (LTDS) method already introduced by Wada et al. [8]. Various samples were prepared by precipitating a strong acidic Ti-bearing solution in an alkaline solution obtained by dissolution of Pb(NO₃)₂ in a KOH solution (pH = 14). The samples were synthesized with varying Pb/Ti atomic ratios (1.0, 2.7, 6.5 and 10) at 70 ^∘C. XRD, TEM, FTIR and DTA/TG techniques were utilized to characterize the obtained powders. The formation of single phase PT was not confirmed for the non-heat treated as precipitated samples in contrast with the results obtained by Wada et al. [8] for BaTiO₃. Further, for the as precipitated samples not subjected to washing process with a Pb/Ti ratio above 1, the formation of unknown crystalline phase/s was detected due to the reaction taken place between Ti-bearing solution and potassium plumbate formed by dissolution of Pb(NO₃)₂ in KOH solution. Applying washing process for these samples gave rise to the partial destruction of the observed structure/s and the formation of an amorphous phase as confirmed by XRD and TEM results. However, calcination of the as precipitated/washed samples at 500 ^∘C and 700 ^∘C for 1 hour gave rise to the formation of PT nanopowder as the main phase with average crystallite sizes in the range of about 11–14.5 nm respectively. Single phase PT nanopowder of an average crystallite size of 13 nm was formed for the sample with a Pb/Ti ratio = 1 when calcined at 500 ^∘C for 1 hour. For the calcined samples with Pb/Ti ratios above 1 the formation of PbO as the second phase, however, was also detected and its level of formation was found to be related to the Pb/Ti ratio.     

Electrostrictive properties of nanosize PbTiO(3)

Properties of nanosize PbTiO(3) are discussed from the standpoint of the effects of crystallite size on electrostrictive behavior. Experimental results based on crystallite size-dependent primary and secondary order parameters (spontaneous polarization and strain) show that the critical crystallite size (CCS) for the stabilization of the cubic paraelectric phase at 298 K is around 15 nm. The CCS inversely scales with the cubic-tetragonal transition temperature (T(tr)). Electrostrictive coefficients exhibit an order of magnitude increase at 28 nm, which is attributed to the anharmonicity of the perovskite lattice. First order calculations indicate that the increase in the electrostrictive coefficients offsets the decrease in spontaneous polarization and results in an increase in piezoelectric moduli suggesting that piezoelectric activity could, in principle, be observed in the nanosize regime.     

Preparation of PbTiO3 fibres using triethanolamine-complexed alkoxide

Abstracts are not published in this journal     

Hierarchical nanostructures by sequential self-assembly of styrene-dimethylsiloxane block copolymers of different periods

Poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) block copolymers with a period as low as 13 nm have been self-assembled on a template formed from PS-b-PDMS of a 34–40 nm period, which is itself templated by micron-scale substrate features prepared using conventional lithography. This hierarchical process provides a simple method for directing the self-assembly of sub-10 nm features and registering them on the substrate.     

Carbon nanostructures/cadmium-sulfide hybrid heterostructures formation

We present a simple method for preparing heterostructures based on cadmium sulfide thin films modified by the addition of carbon nanostructures. For this particular system, we have examined the effect on the photocurrent produced by the addition of multiwall carbon nanotubes or multiwall carbon nanocones between the transparent metallic electrode and CdS, a II–VI semiconductor. Our preliminary results indicate the photocurrent through the semiconductor is strongly modified by the presence of carbon nanotubes or carbon cones.     

Synthesis and characterization of PbTiO3 and Ca and Mn modified PbTiO3 fibres produced by extrusion of diol based gels

Lead titanate precursor gels were prepared using a diol sol-gel system. Water and nitric acid were added to the sols and their effect on the extrusion characteristics of the gels established. After examining the microstructure of the fired fibres obtained from sols containing different water and acid ratios, the merits of incorporating excess lead and/or adding manganese or calcium salts to the sols were also considered. It proved possible to produce unmodified PbTiO₃ fibres that were crack-free having a diameter of ca. 250 m and grain size of ca. 0.3 m with a density of ca. 7.1 g cm^–3. However, the best fibres were achieved from gels containing 2 mol % of added calcium nitrate. These fibres had a density ca. 7.4 g cm^–3 and a grain size of ca. 0.3 m.