Phase and Texture Evolution in Chemically Derived PZT Thin Films on Pt Substrates

The crystallization of lead zirconate titanate (PZT) thin films was evaluated on two different platinum‐coated Si substrates. One substrate consisted of a Pt coating on a Ti adhesion layer, whereas the other consisted of a Pt coating on a TiO₂ adhesion layer. The Pt deposited on TiO₂ exhibited a higher degree of preferred orientation than the Pt deposited on Ti (as measured by the Full Width at Half Maximum of the 111 peak about the sample normal). PZT thin films with a nominal Zr/Ti ratio of 52/48 were deposited on the substrates using the inverted mixing order (IMO) route. Phase and texture evolution of the thin films were monitored during crystallization using in situ X‐ray diffraction at a synchrotron source. The intensity of the Pt₃Pb phase indicated that deposition on a highly oriented Pt/TiO₂ substrate resulted in less diffusion of Pb into the substrate relative to films deposited on Pt/Ti. There was also no evidence of the pyrochlore phase influencing texture evolution. The results suggest that PZT nucleates directly on Pt, which explains the observation of a more highly oriented 111 texture of PZT on the Pt/TiO₂ substrate than on the Pt/Ti substrate.     

Dilution Effects on the Transition Temperature of Ising Monolayers

The effects of dilution on the transition temperature of two dimensional Ising systems (monolayers) have been investigated in lattices with nearest neighbours interactions (n_eff = 4) and for the equivalent-neighbor model with n_eff = 8,12. The dependence of T_c with n_eff is found to be approximately linear for c ≤ 0.4     

硫醇在金属表面自组装成膜的研究进展

金属表面自组装分子膜的研究近年来受到广泛关注,对金属表面自组装单分子膜的研究具有广泛的使用价值与应用价值。本以Au、Ag、Cu、Fe为代表,介绍了硫醇在其表面硫醇自组装成膜的过程、表面膜的结构、表面膜的特点和成膜的机理的研究进展,并且对其发展前景作了展望。     

铝表面自组装成膜工艺的研究

探索出了以KH-460硅烷偶联剂、氟硅酸为主体原料一步法进行铝表面自组装成膜。成膜的最佳条件为:氟硅酸15mL/L,pH值4,镀膜时间15min,温度35℃,KH-460硅烷偶联剂和氟硅酸125mL/L。该工艺适用于涂料涂装前的金属铝表面预处理,自组装膜的综合性能良好,与传统工艺相比具有处理程序简单、槽液稳定、成本低、节能、环保等优点。     

Synthesis of Pt Nanowires Inside Aerosol Derived Spherical Mesoporous Silica Particles

Spherical mesoporous silica particles prepared by evaporation induced self assembly (EISA) were used as templates to form Pt nanowires. Transmission electron microscope (TEM) images of these aerosol-derived silica particles reveal hexagonally ordered pores coiled within each particle, with no obvious termination of the pores on the external surface. Near the particle surface the pores are seen to run parallel to the surface, consistent with the external constraint of spherical geometry. For MCM-41 type mesoporous materials, the pores are straight and accessible at either end for pore filling, but for spherical silica particles prepared by EISA, the pores are not open to the external surface. Hence it is remarkable that Pt nanowires can be formed within the closed pores inside these spherical silica particles, where conventional mechanisms of pore filling would not be expected to be operative. These results suggest that the silica walls in these mesoporous silica allow transport of volatile Pt complexes during wet reduction in H₂. The permeability to gases makes these spherical silica particles especially suitable for gas phase catalytic reactions, while at the same time confining metallic particles within the silica pores.     

Delay Time of Phase Transition in Low-Temperature Phase of Relaxors

The theoretical approach to describe the delay time of a phase transition in low-temperature phase of relaxors is developed. Localized charges create local electric fields which stimulate occurrence of microclusters with local polarization. In high electric fields conduction electrons activate these local levels via shock ionization. The dependences of the delay times of the phase transition on temperature and the value of the external electric field is obtained.     

Transition Temperatures for the Tetragonal-Orthorhombic Phase Transition in the 123 Superconductor

Transition temperatures for the reversible orthorhombic-tetragonal phase transition in the "123'superconductor have been measured using dynamic X-ray diffraction. Results are reported for heating/cooling rates up to 180°C/min and in oxygen partial pressures from 3.2 to 21 kPa and are consistent with a rapid second-order (order-disorder) transition. In air and at cooling rates ≤12°C/min, the transition is perfectly reversible with no detectable hysteresis. At higher heating or cooling rates and at lower oxygen pressures the transition has a definite hysteresis and a measurable dependence on time.     

新疆煤相变机理的研究

利用煤岩学对新疆不同变质程度煤进行了相变机理的研究,探讨了焦炭显微结构对焦炭热性能的影响。当焦炭粗粒、片状组分增加,同性组分减少时,焦炭的应性低,反应后强度提高;当焦炭纤维结构增加,粗粒、片状组分减少时,焦炭的反应性增加,反应后强度下降。     

铵伊利石的高温相变

对山西阳泉煤层黏土煤矸石中的铵伊利石进行了Fourier变换红外光谱分析、电了探针分析、元素分析、热重-差热分析和高温衍射分析.根据化学成分结果,按O10(OH)2及四面体阳离子数之和为4计算得其晶体化学式为:[(NH4)0.65K0.02Na0.03Ca0.01]0.71[Al2.04Mg0.01]2.05[Si3....     

硅碱钙石微晶玻璃中晶相相变

采用高纯的SiO2、Al2O3、KNO3、Na2CO3、CaCO3及CaF2熔融制备了组成为8.4Na2O 1.3Al2O3 5K2O 10.8CaO 64SiO2 10.5 CaF2的硅碱钙石微晶玻璃,采用热力学计算及DTA,XRD和SEM等技术手段对其热处理过程中硅碱钙石和硬硅钙石晶相间的竞争和转变进行研究。经550℃热处理1h后,母体玻璃中有氟化钙晶相析出;在700℃下热处理1h后析出硬硅钙石晶相;在750～850℃下热处理1h后主晶相转变为硅碱钙石。经在700℃下延长微晶玻璃的热处理时间,观察到由硬硅钙石向硅碱钙石的晶相转变。这一转变趋势得到热力学计算的验证。     

Percolation Phase Transition in Combustion of Heterogeneous Mixtures

Combustion of heterogeneous mixtures with a stepwise dependence of the reaction rate on temperature is considered. A twodimensional model of the process is proposed, which takes into account, in addition to other factors, the random distribution of fuel particles in the mixture and nonisothermality of the latter. The flammability limits are compared by methods of numerical simulation for two types of heterogeneous systems with an identical mean density of the fuel: with a uniform distribution of the fuel for all particles of the mixture and with its distribution based on random sampling of particles. It is shown that, as the degree of heterogeneity increases (dimensionless coefficient of heat transfer between the particles, Bi, decreases), the flammability limit for systems of both types becomes significantly higher than its thermodynamic value, and the upper boundary of the limit is twice as high. Differences in flammability limits and burning rates for heterogeneous systems of these types are found. A relationship between the flammability limit of a random system and a percolation phase transition, which occurs in a heterogeneous condensed mixture with scarce inclusions of the fuel, is demonstrated. An analytical approach for evaluation of the threshold concentration of the fuel in such systems, based on the problem of percolation on random nodes, is proposed.     

Compressibility and Phase Transition Kinetics of Lanthanide-Doped Zircon

The structure and compressibility of synthetic lanthanide-doped zircon (ZrSiO₄ with a total of 2.0 mol% trivalent Gd, Dy, Er, Yb, and Y, charge-balanced by addition of P⁵⁺) were determined from static compression experiments to 25.9 GPa. The sample bulk modulus, K _{T 0}=189±1 GPa is 5% lower than K _{T 0} for undoped zircon, and the sample transforms from the zircon to the scheelite structure above 22.6 GPa, 3 GPa greater than the transformation pressure in pure ZrSiO₄. A simple model is presented linking compressibility with unit-cell volume for zircon-structured and scheelite-structured ABO₄ compounds, allowing prediction of the compressibility of zircon-structured vanadates and phosphates.     

Diffuse Phase Transition of Tantalum-Bearing Strontium Barium Niobate

The dielectric constants, ε' and ε", of tantalum-bearing strontium barium niobate (SBNT) ceramics were measured as functions of temperature and frequency. The phase transition of SBNT became ambiguous by adding Ta and the apparent Curie temperature determined from the maximum of ε' had a linear relation with the axial ratio c/a. A dielectric loss peak was observed in the phase transition region of SBNT, and its peak frequency increased with temperature. The loss peak was attributed to dielectric relaxation by the jump between two states with different polarizing directions as a preliminary phenomenon of the phase transition. A model based on the local variation from one unit cell to the next rather than the macroscopic compositional fluctuation in the crystal was proposed for the mechanism of diffuse phase transition.     

Phase Transition Behavior and Large Piezoelectricity Near the Morphotropic Phase Boundary of Lead‐Free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics

The phase transition behavior and piezoelectric properties of (Ba_1?xCa_x)(Zr_0.1Ti_0.9)O₃ and (Ba_0.85Ca_0.15)(Zr_yTi_1?y)O₃ ceramics were investigated in this work to find out the potential factors contributing to large piezoelectricity. It was found that the morphotropic phase boundary (MPB) of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramics was closely related to the presence of an intermediate phase (considered as orthorhombic phase in this work) between rhombohedral (R) and tetragonal (T) phases at a narrow region, which could be carefully adjusted by the temperature and contents of Ca and Zr in the composition. In addition, the maximum piezoelectric and electromechanical coupling coefficients (with d₃₃ = 572 pC/N and k_p = 0.57) were observed near the MPB region close to T phase side, which might be intimately related to the presence of the intermediate phase. This investigation yielded a new sight to understand the mechanism of enhanced piezoelectricity near the MPB.     

固相反应制备Pt/C催化剂

利用固相反应法制得具有较高催化活性的Pt/C催化剂,探讨了制备条件对催化剂性能的影响。结果显示:用水作浸渍介质、n(NaOH)/n(H2PtCl6)=6 4、固相还原剂为聚甲醛时,制得的Pt/C催化剂中Pt粒子的平均粒径为3 8nm。线性扫描伏安结果表明:在30℃、扫速为50mV/s时,制得的Pt/C催化剂在c(CH3OH)=0 5mol/L和c(H2SO4)=0 5mol/L混合溶液中,甲醇氧化的峰电流密度为11 3mA/cm2;而同样条件下,E TEK公司商品化的Pt/C催化剂为9 2mA/cm2。     

Characterization of Pt/SiO2 Model Catalysts at UHV and Near Atmospheric Pressures

Pt/SiO₂ model catalyst samples, prepared under UHV conditions in a contiguous high pressure reactor cell surface analysis chamber, have been characterized via CO oxidation reaction kinetics under elevated pressure conditions (approaching 1 atm). Reaction kinetics are studied as a function of Pt coverage (θ _Pt = 1–10 mL), along with measurements on a Pt(110) single crystal for direct comparison. CO desorption measurements and STM measurements on Pt/SiO₂ films at T = 300 K have been obtained at various θ _Pt. Kinetic results show agreement between observations on single crystal and catalyst samples, and general agreement and correlation is obtained for site calculations across the various methods. Results demonstrate the utility of well characterized model catalyst samples in obtaining qualitative and quantitative reactivity data at elevated pressures.