Synthesis of Single Crystalline ZnO Nanoparticles by Salt-Assisted Spray Pyrolysis

LiNO₃ was used as a shield in the preparation of single crystalline ZnO particles by a spray pyrolysis process in order to prevent agglomeration and enhance the crystallinity of the ZnO. LiNO₃ was added to a precursor solution of zinc acetate dihydrate prior to its atomization by means of an ultrasonic transducer. Agglomerate-free particles having a mean particle size of 26 nm were successfully obtained after washing the product. X-ray diffractometry, field-emission scanning electron micrograph and transmission electron micrograph data indicate that the size and morphology of ZnO were strongly influenced by the operating temperature used and the residence time of the particle in the reactor.     

Raman scattering studies on nanocrystalline BaTiO3 Part II—consolidated polycrystalline ceramics

BaTiO₃ dense ceramics with different grain sizes from 5.6 µm down to 35 nm were thoroughly studied by Raman spectroscopy. The temperature characteristics of optical phonons were compared with those obtained for powders. The micrograined ceramic revealed the well‐known spectrum profiles and transitions, typical for bulk BaTiO₃. On the other hand, the Raman spectra obtained for a nanograined ceramic with an average grain size of 35 nm revealed a tetragonally distorted pure BaTiO₃ phase showing a diffused phase transition behaviour with respect to temperature. Abnormality of phonon damping characteristics for the nanograined ceramic was demonstrated through comparison with powders with various crystallite sizes and the micrograined ceramic. The Curie temperature of the nanograined ceramic was estimated to be 105 °C from the temperature characteristic of a sharp peak at 307 cm⁻¹, which is one of the most specific tetragonal features for bulk BaTiO₃. In the present study, local stabilization of the tetragonal phase in ultra‐fine grains was experimentally demonstrated from comparison between the Raman spectroscopic results for powders and ceramics prepared through microemulsion‐mediated synthesis. Rather long phonon mean free paths can exist even in such ultra‐fine grains, but the phonon characteristics originating from various grains are diffused mainly because of the effect of internal stress. Copyright © 2007 John Wiley & Sons, Ltd.     

Structural phase transitions during high-energy ball milling of BaTiO3

Microstructural characterization of ball milled perovskite BaTiO₃ powders has been done by the modeling of X-ray diffraction profiles. The study reveals that on size reduction, BaTiO₃ powders undergo a continuous, displacive, and diffusionless dynamic phase transitions involving tetragonal (T), monoclinic (M), and orthorhombic (O) symmetry via the second-order type [T?→?(T?+?M)?→?(M?+?O)?→?O] when stimulated by a high-power pulse of pressure in a planetary mill. The order parameter, a phenomenological quantity to describe the general behavior of a system going through phase transitions has been estimated using spontaneous strain calculated from lattice parameters or physical distortions derived from atomic coordinates or both. At room temperature, BaTiO₃ nanoparticle achieved an orthorhombic phase when a critical size (<15?nm) has been reached at later stage of milling (≥70?h). Raman's study reveals similar structural phase transitions sequence on size reduction and TEM study reveals the corresponding particle diameter.     

Effect of uniaxial stress on the dielectric properties of BaTiO3+0.1wt.%Eu2O3 ceramics

ABSTRACT

BaTiO₃+0.1wt.%Eu₂O₃ ceramics were prepared by a solid-state reaction method. The dielectric behavior of these ceramics as a function of uniaxial pressure has been systematically studied. The external stress showed obvious effects on these properties. An increase of the Curie point (T_c) and decrease of the Curie–Weiss temperature (T₀) was observed with increasing pressure, resulting in an increase in the first-order nature of the phase transformation (T_c–T₀ increases). Broadening and flattening of the permittivity versus temperature curves near their maximum was found. The pressure behavior of thermal hysteresis and the ??/?T vs. T plot suggests that the phase transition changes to second-order type with increasing pressure. Furthermore, the Curie–Weiss constant obtained from a modified Curie–Weiss law strongly decreases with increasing pressure, suggesting that the mechanism of phase transition is going to order–disorder type.     

Synthesis of transparent BaTiO3 nanoparticle/polymer composite film using DC field

Transparent BaTiO₃ nanoparticle/polymer composite films were synthesized from titanium-organic film and barium ion in aqueous solution under direct current (DC) field. Titanium-organic precursor was synthesized from titanium isopropoxide, acetylacetone and methacrylate derivative. The UV treatment was effective to increase the anti-solubility of the titanium-organic film during DC processing. BaTiO₃ nanoparticles were crystallized in the precursor films on stainless substrates without high temperature process, as low as 40°C. The crystallite size of BaTiO₃ increased with increasing reaction temperature from 40 to 50 °C at 3.0 V/cm. BaTiO₃ nanoparticles also grew in size with increasing reaction time from 15 min to 45 min at 3.0 V/cm and 50 °C. Transparent BaTiO₃ nanoparticle/polymer films were synthesized on stainless substrates at 3.0 V/cm and 50°C for 45 min.     

Thermodynamic-Controlled Gas Phase Process for the Synthesis of Nickel Nanoparticles of Adjustable Size and Morphology

Gas phase processes are a successful route for the synthesis of nano materials. Nickel particles are used in applications ranging from catalysis to nano electronics and energy storage. The application field defines the required particle size, morphology, crystallinity and purity. Nickel tetracarbonyl is the most promising precursor for the synthesis of high purity nickel particles. Due to the toxicity of this precursor and to obtain an optimal process control we developed a two-step flow type process. Nickel carbonyl and nickel particles are synthesized in a sequence of reactions. The particles are formed in a hot wall reactor at temperatures below 400°C in different gas compositions. Varying the process conditions enables the adjustment of the particle size in a range from 3 to 140 nm. The controllable crystalline habits are polycrystalline, single crystals or multiple twinned particles (MTP). Spectroscopic investigations show an excellent purity. We report about the process and first investigations of the properties of the synthesized nickel nanomaterial.     

Effect of Self-Pumped Phase Conjugation Feedback from a Ce:BaTiO3 Crystal on Lasing Spectrum of a Laser Diode

The effect of self-pumped phase conjugation (SPPC) feedback from a Ce:BaTiO₃ crystal on the lasing spectrum of a commercial laser diode was experimentally investigated, and dependence of the spectrum on the length and reflectivity of the external SPPC cavity was studied. Experimental results showed the optimum reflectivity of the external cavity to be 0.2% for our experimental setup.     

Research in Korea on Gas Phase Synthesis and Control of Nanoparticles

Research activity into the gas phase synthesis of nanoparticles has witnessed rapid growth on a worldwide basis, which is also reflected by Korean research efforts. Nanoparticle research is inherently a multi-disciplinary activity involving both science and engineering. In this paper, the recent studies undertaken in Korea on the gas phase synthesis and control of nanoparticles are reviewed. Studies on the synthesis of various kinds of nanoparticles are first discussed with a focus on the different types of reactors used. Recent experimental and theoretical studies and newly developed methods of measuring and modeling nanoparticle growth are also reviewed.     

六角相NaYF4纳米粒子的合成及粒子尺寸对Tb3+,Er3+下转换效率的影响

采用热溶剂法制备了NaYF4∶Tb3+,Er3+六角相纳米粒子,分析了合成条件对六角相粒子形成的影响。较高的反应温度有利于六角相NaYF4晶体的形成。实验结果表明:六角相是热力学更稳定和更有序的结构,从立方相到六角相的转变是从无序到有序结构的转变。随着尺寸的减小,纳米粒子的下转换效率明显降低。为进一步比较,制备了NaYF4∶Tb3+,Er3+核壳结构的纳米粒子。包覆后的纳米粒子的下转换效率明显提高,其原因是包覆减少了表面缺陷进而降低了表面激发能量的猝灭。