Microstructure and thermophysical characteristics of PbTiO3-based ceramics

Precursor powders of a modified lead titanate-based ceramic material have been synthesized by two different chemical techniques and also by the conventional attrition milling method. The influence of powder processing techniques on the phase development, powder morphology and thermophysical behaviour of the material have been examined. The study shows that the above properties in this material are strongly dependent on the powder synthesis method as well as the thermal treatment of the precursor powders.     

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.     

Study on the properties of a nanocrystal and polymer composite PbTiO3/PEK-c film with optical anisotropy

Composite thin films of PbTiO₃ nanocrystals and PEK-c polymer for applications in nonlinear optical devices were prepared by spin coating. The size of PbTiO₃ nanocrystals was estimated to be 30–40 nm. The microstructure of PbTiO₃/PEK-c composite polymer film before and after poling was analyzed by X-ray diffraction, which show that this film is c axis-orientated. The poled composite film displayed the refractive index anisotropy. In this sample the TE- and TM-indices differences are found to be 0.02945 for 633 nm and 0.03915 for 414 nm. The electro-optic coefficient ₃₃ of poled composite film was measured to be 12.89 pm V^–1 at 633 nm by the transmission technique. The dielectric constant of it at 100 KHz under room temperature was determined to be 7.32. The figure of merit F ₂ was estimated to be 492. In addition, a relaxation process was observed in the time range of 28 days and the relaxation time constant was calculated to be 2393 min.     

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.     

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.     

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.     

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.     

Deposition of PbTiO3 film by the spray-ICP technique

PbTiO₃ thin films were prepared on various substrates by spraying an ultrasonically atomized aqueous solution of Pb(NO₃)₂ + TiO (NO₃)₂ into an inductively coupled plasma (ICP) under atmospheric pressure. Single-phase PbTiO₃ with perovskite structure was obtained at 500–650 °C. The perovskite obtained below 600 °C showed less tetragonality due to the effect of grain size. The PbTiO₃ films crystallized with preferred (1 1 1) and (0 0 1) orientations on sapphire (0 0 1) and MgO (1 0 0), respectively. Based on the analysis of ICP emission spectra, it is suggested that a reoxidation of titanium preceded that of lead in the plasma, and also that OH in the plasma played an important role in the deposition of PbTiO₃.     

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。     

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.     

Unconventional polarization arrangements in PbTiO3 single crystals

Polarization arrangements and ferroelectric domain structures of poly-domain flux-grown PbTiO₃ crystals have been studied using optical and electron microscopy. Most of the specimens show band arrangements which may correspond to surface relief characteristics of as-grown crystals. Drawing schematic polarization configurations, one finds that head-to-head, tail-to-tail, or other unconventional polarization configurations exist constantly in PbTiO₃ crystals, indicating that the high electrical energy configurations are quite common in lead titanate crystals. Investigations on etched crystals indicate that crystals grown under different conditions show similar domain structure and polarization characteristics.     

Effect of synthesis conditions on the structure of PbTiO3

The phase composition of PbTiO₃ samples prepared from PbO + TiO₂ and PbO + TiO₂ · H₂O mixtures is determined. The effect of mechanical stress on the structure of PbTiO₃ prepared by high-temperature firing of a PbO + TiO₂ mixture is investigated experimentally. It is shown that low-temperature synthesis yields not only the perovskite phase of PbTiO₃ but also an oxygen-deficient pyrochlore phase with an increased lattice parameter. With increasing temperature, the content of the latter phase drops to zero. The pyrochlore-perovskite phase transition in PbTiO₃ is discussed in terms of crystal chemistry and close packing of atoms.     

Hierarchical nanostructures of PbTiO3 through mesocrystal formation

Novel hierarchical self-assembled structures; bur-like PbTiO3 nanostructures were made by self-assembly of PbTiO3 nanocrystals under hydrothermal conditions using sodium dodecylbenzene sulfonate surfactant. The bur-like nanostructures exhibit a unique geometrical shape with cores of agglomerated nanocrystals and outershells of nanorods. The nanorods were between 30 nm and 100 nm in diameter and from several hundred nm up to 2 microm in length. We demonstrate that these nanostructures are formed in a two step process where agglomeration of PbTiO3 nanoparticles into microspheres occurs in a first step, followed by assembly of cube-shaped nanoparticle building blocks into PbTiO3 mesocrystals in a second step. The mesocrystals continuously grow into nanorods from the surface of the microspheres acting as a substrate.     

Preparation of PbTiO3 fibres using triethanolamine-complexed alkoxide

Abstracts are not published in this journal     

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.