In situ measurement of crystallization of oxide thin films during irradiation with pulsed UV laser in chemical solution deposition process

The epitaxial and polycrystalline growth of lanthanum strontium manganite films on single crystalline strontium titanate and lanthanum aluminate substrates, respectively, under the irradiation with XeCl lasers in the excimer laser-assisted metal organic deposition (ELAMOD) process have been previously reported. In order to investigate the growth phenomena, we monitored the thermal radiation from the sample surfaces irradiated with a pulsed ultraviolet laser in situ with near-infrared sensors. The cooling of the lanthanum strontium manganite films on strontium titanate substrates was significantly slower than that of films on lanthanum aluminate substrates. A similar behavior was also observed by the numerical simulation study. This difference in the cooling decay curves may play an important role in the mode by which crystal growth occurs in the ELAMOD process.     

Electro- and Magnetotransport near a LaAlO3/SrTiO3 Interphase Boundary

Comparison of the channel spectra of medium energy ion scattering, visualized for LaAlO₃/(001)SrTiO₃ heterostructures with a thickness of the lanthanum aluminate layer of one to six unit cells, indicates that the lanthanum aluminate layer grows coherently on a TiO₂-terminated surface of a strontium titanate substrate. The resistance of the interphase boundary in the heterostructure with a thickness of the LaAlO₃ layer of six unit cells decreased with temperature. At T < 100 K, the positive magnetoresistance and Hall mobility of electrons increased sharply with decreasing temperature.

     

Reduction of Cu2O islands grown on a Cu(100) surface through vacuum annealing

The reduction of Cu2O islands grown on Cu(100) surfaces through vacuum annealing was visualized by an in situ ultrahigh vacuum transmission electron microscope. The shrinkage of the island followed a linear decay behavior. The complete reduction of the oxide islands leads to the formation of nanoindentations on the Cu surfaces. A simple phenomenological kinetic model based on the dissociation along the island perimeter suitably describes the reduction behavior of the surface oxide islands.     

Mechanochemically assisted synthesis of La0.7Sr0.3MnO3 nanoparticles and induction heating properties of the composites with hydroxyapatite

Perovskite lanthanum strontium manganese oxide (LSMO, strontium-substituted lanthanum manganite) La_0.7Sr_0.3MnO₃ nanoparticles were synthesized via the low-temperature calcination of the precursor, which was prepared using a mechanochemical route. A powder mixture of lanthanum chloride, strontium chloride, manganese chloride and sodium carbonate was high-energy milled by a planetary ball mill under semiwet (moist) conditions to obtain the precursor. To study the mechanochemical effects on the formation of LSMO, a thermogravimetric (TG) analysis was conducted for the precursors prepared under various conditions; the precursors and the intermediates formed during calcination were identified by X-ray diffraction (XRD). The calcination of the milled precursor at 600 °C resulted in the formation of LSMO nanoparticles with good induction heating properties. The LSMO/hydroxyapatite composites exhibited rapid temperature increases in an AC magnetic field. The obtained results demonstrate that the LSMO nanoparticles and LSMO/hydroxyapatite composites are promising candidates for magnetic hyperthermia treatments.     

Effecting factors of the emission spectral characteristics of rare-earth strontium aluminate for anti-counterfeiting application

The rare-earth strontium aluminate phosphor with stable physical and luminescent performances is a suitable rare-earth luminescent material for spectrum-fingerprint anti-counterfeiting fiber. In order to promote further the development of variety and the improvement of anti-counterfeiting effects of spectrum-fingerprint fiber, in this research, several kinds of rare-earth strontium aluminates and spectrum-fingerprint anti-counterfeiting fiber were prepared by solid-state reaction and special spinning technique, respectively. The effects upon manufacturing elements of strontium aluminate including calcining temperature, Al/Sr ratios, the addition of H₃BO₃, Eu²⁺ and Dy³⁺ and external environmental factors of applications such as fiber-forming polymer on emission spectral characteristics were investigated systematically in the anti-counterfeiting application. The results showed that with the increase in the calcining temperature, the amounts of H₃BO₃ doping and the concentration of Eu²⁺ and Dy³⁺, the emission intensity of rare-earth strontium aluminate increased and reached to the peak at a certain point at start, and then decreased gradually beyond this point. Al/Sr molar ratios influenced not only the intensity but also the wavelength of emission. Fiber-forming polymer had little effect on the emission wavelength and the shape in the luminescence, but greatly lowered the intensity of emission.     

Highly efficient, 0.84 slope efficiency, 901 nm, quasi-two-level laser emission of Nd in strontium lanthanum aluminate

The possibility of using direct pumping into the emitting level of the Nd3+ ion in magnesium-compensated strontium lanthanum aluminate (Sr(1-x)La(x-y)Nd(y)Mg(x)Al(12-x)O19) to improve 900 nm 4F(3/2) --> 4I(9/2) laser emission is discussed. Selection of the composition parameters x and y for optimization of laser emission and reduction of heat generation is based on the spectroscopic and crystal growth characteristics. Pumping in the 865.5 nm absorption band 4I(9/2)(Z1) --> 4F(3/2)(R1) transforms the laser process into a quasi-two-level scheme of very low (below 4%) quantum defects. A very high slope efficiency (over 84%) for 901 nm continuous-wave laser emission is demonstrated with Ti:sapphire laser pumping in this band for a crystal with x = 0.4 and y = 0.05.     

Magnetic and Resistive Properties of Magnetite/Iridate Heterostructures

Journal of Experimental and Theoretical Physics - A technique is developed to grow epitaxial heterostructures consisting of strontium iridate (SrIrO3) and lanthanum–strontium manganite...     

密封容器中后处理制备Tl2Ba2CaCu2Oy高温超导薄膜及其性能研究

以铝酸镧（001）单晶为基片，采用两步法制备Tl2Ba2CaCu2Oy（Tl 2212）高 温超导薄膜.首先，利用脉冲激光沉积（PLD）工艺沉积Ba2CaCu2Ox非晶前驱体薄膜；然后，前驱体薄膜在高温（720—850℃）下密封钢容器里铊化结晶形成Tl 2212薄膜.XRD结果表明Tl2212 薄膜是沿c轴方向生长的，其相组成为Tl 2212，摇摆曲线（0012）的半高宽为0.72° ，SEM图像显示其表面光滑平整，其零电阻温度为106.2K. 关键词： Tl 2212超导薄膜 脉冲激光沉积     

火焰原子发射光谱法直接测定矿泉水中锶

本文介绍了用原子吸收光谱仪的发射方式火焰原子发射光谱法直接测定矿泉水中锶。使用钾、钠混合消电离剂和镧释放剂，消除电离干扰和共存元素干扰，本法灵敏度高，可直接测定矿泉水中微量锶。本法准确、可靠，结果令人满意。     

基于电子顺磁共振的锶铁氧体磁特性研究

为了研究配料、温度、氧环境和掺杂等条件对锶铁氧体的磁性能的影响问题, 利用溶胶-凝胶法制备了锶铁氧体粉末, 建立了一种基于电子顺磁共振技术研究锶铁氧体粉末的磁特性的方法. 用电子顺磁共振波谱仪对烧结后的产物进行测试发现: 400 ℃预烧下, 锶铁摩尔比为1:9时, 中间产物顺磁相α-Fe₂O₃含量最多, 高于400 ℃时其含量减少, 亚铁磁相增加, 并确定最佳煅烧温度介于800-900 ℃. 这是由于外磁场和其他磁场综合作用产生亚铁磁相, 进而产生较强的磁矩相互作用所致. 结合工业实际应用, 发现缺氧退火环境下, 顺磁相α-Fe₂O₃含量较大, 不利于亚铁磁相生成; X-射线衍射(XRD)表征结果表明: 除了少量杂相, 其余均为顺磁相和亚铁磁相; 电子顺磁共振谱和XRD 谱检测结果综合表明, 锶铁摩尔比为1:9时, 最终产物的顺磁相含量最少, 亚铁磁相含量最多, 磁性最强; 毫特斯拉计的剩磁检测结果也证实了上述结果. 掺杂实验发现镧离子占锶镧总摩尔数的20% 至30% 时, 能够有效降低顺磁相的产生, 增强最终产物的亚铁磁性.     

Strong mechanoluminescence induced by elastic deformation of rare-earth-doped strontium aluminate phosphors

When rare-earth-doped strontium aluminate phosphor mixed in an epoxy resin, is deformed elastically by applying a uniaxial pressure, then initially the mechanoluminescence (ML) intensity increases with time, attains a peak value I_m at a particular time t_m, and later on it decreases with time. After t_m, initially, the ML intensity decreases exponentially at a fast rate and then it decreases exponentially at a slow rate. The ML appears after a threshold pressure and then, initially at low pressure, the peak intensity I_m of ML increases linearly with the magnitude of applied pressure, and for high pressure, I_m increases exponentially with the magnitude of applied pressure. The value of I_m increases linearly with the density of filled hole traps. The ML emission also takes place during the release of applied pressure. There should be a significant effect of temperature on the ML intensity of rare-earth-doped strontium aluminate phosphors. The ML intensity of rare-earth-doped strontium aluminates decreases with successive number of the applications of pressure and the diminished ML intensity can be recovered with the exposure of the samples to UV-radiation. The ML spectra of rare-earth-doped strontium aluminate phosphors are similar to their photoluminescence spectra. As only the piezoelectric-phase of the strontium aluminate phosphors exhibit ML during their elastic deformation, the ML emission can be attributed to the piezoelectrification of the crystals. Considering that the piezoelectric field causes decrease in the trap-depth of the hole traps and, therefore, the holes transferred from traps to the valence band recombine with (Eu¹⁺)^* ions, whereby the Eu²⁺ ions are excited, expressions are derived for different parameters of ML, which are able to satisfactorily explain the experimental results. It is shown that the lifetimes of holes in the shallow traps in stressed and unstressed materials, and the threshold pressure P_t for the ML emission, and other parameters of the ML, can be determined from the ML measurements. Finally, the criteria for tailoring strong elasico-mechanoluminescent materials are explored.     

Processing and characterization of porous electrochemical cells for flue gas purification

In the present work, porous electrode materials lanthanum strontium manganate (LSM)-gadolinium-doped cerium oxide (CGO) and electrochemical cells LSM-CGO + CGO were fabricated via the processes of slurry preparation, tape casting and lamination, and sintering. Graphite, wheat starch, and polyamide powders were used as pore formers, respectively, in order to investigate their effects on shrinkage, flow rate, porosity, and average pore size of the sintered samples. The observation from scanning electronic microscope (SEM) revealed different microstructures caused by different pore formers. Porous, flat, and crack-free electrochemical cells were successfully achieved using the present ceramic processing route. The produced cells could potentially be used for flue gas purification.     

3D KMC simulations of crater growth during the reduction of oxide nanoislands on metal surfaces

The homoepitaxial growth of Cu nanocraters induced by thermal reduction of Cu₂O nanoislands on Cu(100) surfaces is simulated using a three-dimensional (3D) kinetic Monte Carlo (KMC) model by incorporating surface diffusion, attachment and detachment Cu adatoms dislodged from reducing Cu₂O islands. The craters are observed to grow continuously in rim height and rim slopes while remaining relatively constant in rim width in the course of the oxide decomposition. Such a growth behavior is attributed to the climbing uphill of Cu adatoms released from the perimeter of the reducing Cu₂O island at the crater bottom. The observed decay of the rim height and slopes after completion of the reduction of oxide islands suggests that these surface craters are thermodynamically unstable at high temperatures.     

Modifications of interface chemistry of LSM-YSZ composite by ceria nanoparticles

A porous composite electrode LSM-YSZ (lanthanum strontium manganite and yttria stabilized zirconia) was impregnated with different amounts of SDC (samarium substituted ceria) nanoparticles. The materials were investigated with X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy to determine the microstructure, the interface chemistry and the surface chemistry of the various impregnated samples. The SDC nanoparticles cover the surface of the LSM-YSZ backbone to a large extent; they are approximately 5-20 nm in diameter and have a cubic crystal structure. Low concentrations of lanthanum and manganese originating from LSM were detected within SDC particles. It was also observed that the relative atomic concentration of strontium increased on the LSM-YSZ surface with increasing amount of SDC nanoparticles. These findings are related to the applied nanoparticle impregnation method. It is indicated that interactions between surfactant, nanoparticles, impregnation solution and the LSM-YSZ composite take place which can locally affect the surface and interface chemistry of the investigated materials.     

Grain boundary ridge formation during initial high temperature oxidation of Mn/Al TRIP steel

Confocal scanning laser microscopy (CSLM) was used in real-time observation of alloy element oxidation of a Mn/Al TRIP steel in an Ar–O₂ atmosphere. CSLM images reveal a marked role of grain boundaries in the overall initial oxidation kinetics of the alloy, and consequently in the morphology of the initial surface oxide. The oxidation on the alloy surface is dominated by the formation of Mn-rich oxide ridges along grain boundary traces on the surface. Oxide ridge formation kinetics was quantified by measurements on images extracted from real-time recordings of surface oxide evolution. Oxide ridge growth was found to take place at a constant rate. Scanning electron microscopy (SEM) images of the oxidized surfaces showed homogenous oxide ridges along straight grain boundary traces and heterogeneous oxide ridges along non-straight grain boundary traces. A transport mechanism of Mn to the surface is proposed, which relies on grain boundary segregation of Mn and on a relationship between grain boundary diffusivity and grain boundary character. It is suggested that when regarding alloys with significant grain boundary segregation of a solute, separate Wagner balances for internal vs. external oxidation is required for the grain lattices and the grain boundaries, respectively.     

Yttrium segregation and surface phases of yttria-stabilized zirconia (1 1 1) surface

Surface segregation of yttria-stabilized zirconia (YSZ) was studied via first-principles computations and thermodynamics. For the cubic YSZ (1 1 1) surface, yttrium can segregate only to a subsurface layer, and these segregation phases are terminated at the surface by defective oxygen layers with honeycomb structure. The segregation is independent of the bulk yttrium concentration at high oxygen partial pressures or low temperatures. At very low oxygen partial pressures and high temperatures there is no surface yttrium segregation and the surface is terminated by O–Zr. Our results provide a reasonable explanation for previous experimental work, and also a framework for extending our understanding of cation segregation in oxide surfaces.     

Growth of oriented crystalline Ag nanoislands on air-exposed Si(0 0 1) surfaces

Growth of Ag islands under ultrahigh vacuum condition on air-exposed Si(0 0 1)-(2 × 1) surfaces has been investigated by in-situ reflection high energy electron diffraction (RHEED). A thin oxide is formed on Si via exposure of the clean Si(0 0 1)-(2 × 1) surface to air. Deposition of Ag on this oxidized surface was carried out at different substrate temperatures. Deposition at room temperature leads to the growth of randomly oriented Ag islands while well-oriented Ag islands, with (0 0 1)_Ag||(0 0 1)_Si, [1 1 0]_Ag||[1 1 0]_Si, have been found to grow at substrate temperatures of ≥350 °C in spite of the presence of the oxide layer between Ag islands and Si. The RHEED patterns show similarities with the case of Ag deposition on H-passivated Si(0 0 1) surfaces.     

Quasi-ordered nanostructures on the surface of strontium titanate

The results of the investigation of the surface of strontium titanate single crystals after treatment with high-energy plasma are presented. The surface morphology of the strontium titanate single crystals and the change in its characteristics after plasma treatment have been studied using electron scanning and atomicforce microscopy. A change in the electronic state of a part of the titanium ions and a change in the stoichiometry in the modified near-surface layer have been found by the method of valence shift of X-ray lines. A preliminary analysis has been made of the conditions providing the formation of single- and two-level systems of ordered crystallites with sizes of 10⁻⁷–10⁻¹⁰ m on the surface of single-crystal strontium titanate with impurities of ions of the iron and lanthanum groups.     

Investigation of chemisorbed oxygen, surface segregation and effect of post-treatments on La0.8Sr0.2MnO3 powder and screen-printed layers for solid oxide fuel cell cathodes

In order to better understand the mechanism of the reaction of oxygen reduction at the surface of strontium doped lanthanum manganites (LSM) cathodes in solid electrolyte fuel cells (SOFC), the surface properties of La_0.8Sr_0.2MnO₃ powders and screen-printed layers have been characterised by various techniques.Strontium enrichment at the surface has been evidenced by X-ray photoelectron spectroscopy according to the conditions of annealing (temperature, oxygen pressure) and polarisation treatments of the samples.The interaction between oxygen and La_0.8Sr_0.2MnO₃ for SOFC cathodes has been studied by thermo-programmed desorption, in situ infrared spectrometry and calorimetry. The results indicate that various adsorbed oxygen species may exist on the surface of LSM depending on temperature.The presence of various adsorbed oxygen species and the surface Sr segregation are important factors to consider in the mechanism of oxygen reduction at LSM SOFC cathodes since they could be responsible for many discrepancies between the interpretations that can be found in the literature data.     

Stoichiometric lanthanum chromite based ceramic interconnects with low sintering temperature

Ceramic interconnects for use in solid oxide fuel cells are expected to operate between 800∼1000 °C, sinter between 1400∼1500 °C to allow co-firing and meet a number thermal mechanical requirements. The perovskite type (ABO₃) lanthanum chromite based materials have emerged as a leading candidate that will meet these criteria by varying the composition on the A and B sites. A need therefore exists to determine this material's temperature dependent electrical and mechanical properties with respect to these site substitutions. In this investigation, oxide powders were prepared by the glycine-nitrate process. Ionic substitutions were carried out on A sites with calcium or strontium, and B sites with cobalt and aluminum, respectively. Only stoichiometric compositions were considered for the sake of stability. The powders and their sinterability were investigated by XRD, SEM, dilatometry and density measurements. The sintered materials were further examined by SEM, thermal expansion and electric conductivity measurements in order to elucidate the resulting microstructure, electrical and mechanical properties.