Ferrimagnetism, antiferromagnetism, and magnetic frustration in La2-xSrxCuRuO6 (0 <= x <= 1)

We studied structural and magnetic properties of a series of insulating double perovskite compounds, La2-xSrxCuRuO6 (0 <= x <= 1), representing doping via A-site substitution. The end members La2CuRuO6 and LaSrCuRuO6 form in monoclinic structure while the intermediate Sr doped compounds stabilize in triclinic structure. The Cu and Ru ions sit on alternate B sites of the perovskite lattice with similar to 15% antisite defects in the undoped sample while the Sr-doped samples show a tendency to higher ordering at B sites. The undoped (x = 0) compound shows a ferrimagnetic-like behavior at low temperatures. In surprising contrast to the usual expectation of an enhancement of ferromagnetic interaction on doping, an antiferromagnetic-like ground state is realized for all doped samples (x > 0). Heat capacity measurements indicate the absence of any long-range magnetic order in any of these compounds. The magnetic relaxation and memory effects observed in all compounds suggest glassy dynamical properties associated with magnetic disorder and frustration. We show that the observed magnetic properties are dominated by the competition between the nearest-neighbor Ru-O-Cu 180 degrees superexchange interaction and the next-nearest-neighbor Ru-O-O-Ru 90 degrees superexchange interaction as well as by the formation of antisite defects with interchanged Cu and Ru positions. Our calculated exchange interaction parameters from first principles calculations for x = 0 and x = 1 support this interpretation.

Platinum Ion-Doped TiO2: High Catalytic Activity of Pt2+ with Oxide Ion Vacancy in Ti1-x4+Ptx2+O2-x Compared to Pt4+ without Oxide Ion Vacancy in Ti1-x4+Ptx4+O2

Ti0.97Pt0.032+O1.97 and Ti0.97Pt0.034+O2 have been synthesized by a solution combustion method using alanine and glycine as the fuels, respectively. Both crystallize in anatase TiO2 structure with 15 nm average crystallite size. X-ray photoelectron spectroscopy (XPS) confirmed Pt ions are in the 2+ state in Ti0.97Pt0.03O1.97 (alanine) and 4+ state in Ti0.97Pt0.03O2 (glycine). The rate of CO oxidation occurring over Ti0.97Pt0.032+O1.97 (0.76 mu mol.g(-1).s(-1)) is similar to 10, times more than that over Ti0.97Pt0.034+O2 at 60 degrees C (0.08 mu mol.g(-1).s(-1)). A large shift in 100% hydrocarbons conversion to lower temperature was observed for Pt2+ ion-substituted TiO2 relative 10 that for Pt4+ ion-substituted TiO2. After reoxidation of the reduced compound by H-2 as well as CO, Pt ions are stabilized in mixed valences, 2+ and 4+ states. The role of oxide ion vacancy has been demonstrated by CO oxidation and H-2 + O-2 recombination reactions in the presence and absence of O-2. We analyze the activated lattice oxygens upon substitution of Pt2+ and Pt4+ ions in TiO2, using first-principles density functional theory (DFT) calculations with supercells of Ti31Pt1O63, Ti30Pt2O62, and Ti29Pt3O61 for Pt2+ ion substitution and Ti31Pt1O64, Ti30Pt2O62, and Ti29Pt3O61 for Pt4+ ion substitution in TiO2. We find that the local structure of Pt2+ ion has a distorted square planar geometry and that of Pt4+ ion has an octahedral geometry similar to that of Ti4+ ion in pure TiO2. The change in coordination of Pt2+ ion gives rise to weakly bonded oxygens, and these oxygens are involved in high rates of catalytic reaction. Thus, the high catalytic activity results from synergistic roles of Pt2+ ion and oxide ion vacancy and weakly bonded lattice oxygen.

Phase boundary at x=0.03 and its anomalous influence on the structure and properties in the lead-free piezoelectric (1-x)Na1/2Bi1/2TiO3-(x)BaTiO3

The complexity associated with local structures continues to pose challenges with regard to the understanding of the structure-property relationship in Na1/2Bi1/2TiO3-based lead-free piezoceramics. (1-x)Na1/2Bi1/2TiO3-(x)BaTiO3 is an extensively studied system because of its interesting piezoelectric properties. Recently, a room temperature phase boundary was reported at x = 0.03 in this system Ma et al., Adv. Funct. Mater. 23, 5261 (2013)]. In the present work we have examined this subtle phase boundary using x-ray diffraction, neutron diffraction, dielectric measurements as a function of composition (x < 0.06), temperature, and electric field. Our results show that this boundary separates an R3c + Cc-like structural state for x < 0.03 from an R3c+ cubiclike structural state for 0.03 <= x <= 0.05 in the unpoled specimens. This phase boundary is characterized by an anomalous reduction in the depolarization temperature, and a suppression of the tetragonal distortion of the high temperature P4bm phase. Our results also provide the clue to understand the pathway leading to the cubiclike structure of the critical composition x = 0.06, known for its highest piezoelectric response.

Macropores generated during shrinkage in two paddy soils using X-ray micro-computed tomography

Soil shrinkage curve represents a decrease of total porosity or an increase of bulk density with water loss. However, our knowledge of the dynamics of pores and their geometry during soil shrinkage is scarce, partially due to lack of reliable methods for determining soil pores in relation to change in soil water. This study aimed to investigate the dynamics of macropores (>30 mu m) of paddy soils during shrinkage. Two, paddy soils, which were sampled from one paddy field cultivated for 20 years (YPF) and the other one for over 100 years (OPF), represented difference in crack geometry in the field. Macropore parameters (volume, connectivity, and orientation of pores) and soil shrinkage parameters were determined on the same undisturbed soil cores by X-ray microtomography and shrinkage curve, respectively. Macroporosity was on average four times larger in the YPF than in the OPF whereas the shrinkage capacity was lower in the YPF as compared to the OPF (0.09 vs. 0.15 COLE). Soil shrinkage increased the volume of pores by 3.7% in the YPF and by 1.6% in the OPF as well as their connectivity. The formation of macropores occurred mostly in the proportional shrinkage phase. As a result, the slope of the proportional shrinkage phase was smaller in the YPF (0.65) than in the OPF (0.89). New macropores were cracks and extended pre-existing pores in the range of 225-1215 pm size without any preferential orientation. This work provides image evidences that in paddy soils with high shrinkage capacity more macropores are generated in the soil presenting a smaller proportional shrinkage slope. (C) 2015 Elsevier B.V. All rights reserved.

室温铁磁性半导体Mn_xGa_(1-x)Sb

采用离子注入、离子沉积及后期退火方法制备了稀磁半导体单晶Mn_xGa_(1-x)Sb，在室温下（300 K）获得了单晶的磁滞回线。用X射线衍射方法分析了铁磁性半导体单晶Mn_xGa_(1-x)Sb的结构，用电化学C-V法分析了单晶的载流子浓度分布。由X射线衍射得知，Mn_xGa_(1-x)Sb中Mn含量逐渐由近表面处的x = 0.09下降到晶片内部的x = 0。电化学C-V测得单晶的空穴浓度高达1 * 10~(21)cm~(-3)，表明Mn_xGa_(1-x)Sb单晶中大部分Mn原子占据Ga位，起受主作用。

Relation between weight and linear measurement of shell in C. madrasensis (Preston)

Relation of weight to height, length and breadth in the Indian backwater oyster Crassostrea madrasensis (Preston) is reported. The relative importance of the variables on weight was found to be height, length and breadth in their order of preference. The multiple regression V = -0.4017 + 0.46743 X + 0.8278 Y + 0.1130 Z can be used to estimate the meat weight (logarithm) for given dimensions of length, height and breadth (all in logarithms). An exponential relation between weight and height is also observed.

Storage of photoexcited electron-hole pairs in an AlAs/GaAs heterostructure created by electron transfer in real and kappa spaces

The storage of photoexcited electron-hole pairs is experimentally carried out and theoretically realized by transferring electrons in both real and k spaces through resonant Gamma - X in an AlAs/GaAs heterostructure. This is proven by the peculiar capacitance jump and hysteresis in the measured capacitance-voltage curves. Our structure may be used as a photonic memory cell with a long storage time and a fast retrieval of photons as well.

Formation mechanism of electric field domains

Hydrostatic pressure measurements are used to investigate the formation mechanism of electric field domains in doped weakly-coupled GaAs/AlAs superlattices. For the first plateau-like region in the I-V curve, two kinds of sequential resonant tunnelling are observed. For P<2 kbar the high-field domain is formed by the Gamma-Gamma process, while for P>2 kbar the high-field domain is formed by the T-X process. For the second plateau-libe region, the high-field domain is attributed to Gamma-X sequential resonant tunnelling. (C) 1998 Elsevier Science B.V. All rights reserved.

DETERMINATION OF THE X-CONDUCTION-SUBBAND ENERGIES IN TYPE-II GAAS/ALAS/GAAS QUANTUM-WELL BY DEEP-LEVEL TRANSIENT SPECTROSCOPY

Using deep level transient spectroscopy (DLTS) the X conduction-subband energy levels in an AlAs well sandwiched by double GaAs layers were determined. Calculation gives eight subbands in the well with well width of 50 Angstrom. Among them, five levels and the other three remainders are determined by using the large longitudinal electron effective mass m(1)(1.1m(0)) and transverse electron effective mass m(t)(0.19m(0)) at X valley, respectively. Two subbands with the height energies were hardly detectable and the other six ones with lower energies are active in the present DLTS study. Because these six subbands are close to each other, we divided them into three groups. Experimentally, we observed three signals induced from the three groups. A good agreement between the calculation and experiment was obtained. (C) 1995 American Institute of Physics.

室温铁磁性半导体Mn_xGa_(1-x)Sb

采用离子注入、离子沉积及后期退火方法制备了稀磁半导体单晶Mn_xGa_(1-x)Sb，在室温下（300 K）获得了单晶的磁滞回线。用X射线衍射方法分析了铁磁性半导体单晶Mn_xGa_(1-x)Sb的结构，用电化学C-V法分析了单晶的载流子浓度分布。由X射线衍射得知，Mn_xGa_(1-x)Sb中Mn含量逐渐由近表面处的x = 0.09下降到晶片内部的x = 0。电化学C-V测得单晶的空穴浓度高达1 * 10~(21)cm~(-3)，表明Mn_xGa_(1-x)Sb单晶中大部分Mn原子占据Ga位，起受主作用。

预注入对Si_（1-x）C_x合金形成的影响

室温下在单晶Si中注入(0.6-1.5)at%的C原子，部分样品在C离子注入之前在其中注入~(29)Si~+离子产生损伤，然后在相同条件下利用高温退火固相外延了Si_(1-x)C_x合金，研究了预注入对Si_(1-x)C_x合金形成的影响。如果注入C离子的剂量小于引起Si非晶化的剂量，在950℃退火过程中注入产生的损伤缺陷容易与C原子结合形成缺陷团簇，难于形成Si_(1-x)C_x合金，预注入形成的损伤有利于合金的形成。随着C离子剂量的增大，注入产生的损伤增强，预注入反而不利于Si_(1-x)C_x合金的形成，但当注入C原子的浓度超过固相外延的溶解度时，预注入的影响可以忽略。退火温度升高到1050℃，无论预注入还是未预注入样品，C含量低的合金相仍然保留，而C含量高的合金相大部分消失。

C离子注入Si中Si-C合金的形成及其特征

利用离子注入和高温退火的方法在Si中生长了C含量为0.6%-1.0%的Si_(1-x)C_x合金，研究了注入过程中产生的损伤缺陷，注入C离子的剂量及退火工艺对合金形成的影响，探讨了合金的形成机理及合金产生的应变分布的起因，如果注入的C离子剂量小于引起Si非晶化的剂量，退火过程中注入产生的损伤缺陷容易与C原子结合形成缺陷团簇，难于形成Si_(1-x)C_x合金，而预先利用Si离子注入引进损伤有利于Si_(1-x)C_x合金的形成；但如果注入的C离子可以引起Si的非晶化，预先注入产生的损伤缺陷不利于Si_(1-x)C_x合金的形成。与慢速退火工艺相比，快速热退火工艺有利于Si_(1-x)C_x合金的形成。离子注入的C原子在空间分布不均匀，退火过程中将形成应变不同的Si_(1-x)C_x合金区域。

X射线低剂量多次辐射对小鼠外周血淋巴细胞的影响

为了评估低剂量多次辐射对健康机体产生的生物学风险。检测了X射线多次照射对BALB/c小鼠免疫系统的影响。采用X射线全身多次照射,第1天照射0.07 Gy,之后每天照射0.08 Gy共12d,剂量率0.2 Gy/min,累积剂量为0、0.07、0.23、0.39、0.55、0.71、0.87和1.03 Gy时取样。照射24 h后取血,用流式细胞仪检测外周血中免疫细胞周期和死亡的变化。结果表明。外周血淋巴细胞的周期在0.39和1.03 Gy时,被阻滞在G_2/M期,在0.07、0.23、0.71和0.87Gy时,被阻滞在G_0/G_1期;细胞的死亡随着累积剂量的增加而增加,在0.71Gy时达到峰值。经过X射线多次全身照射小鼠后,可引起外周血淋巴细胞周期和死亡比例发生变化,符合线性平方模型,造成其免疫系统一定的损伤。

C离子注入Si中Si-C合金的形成及其特征

利用离子注入和高温退火的方法在 Si中生长了 C含量为 0 .6 %— 1.0 %的 Si1 - x Cx 合金 ,研究了注入过程中产生的损伤缺陷、注入 C离子的剂量及退火工艺对合金形成的影响 ,探讨了合金的形成机理及合金产生的应变分布的起因 .如果注入的 C离子剂量小于引起 Si非晶化的剂量 ,退火过程中注入产生的损伤缺陷容易与 C原子结合形成缺陷团簇 ,难于形成 Si1 - x Cx 合金 ,而预先利用 Si离子注入引进损伤有利于 Si1 - x Cx 合金的形成 ;但如果注入的C离子可以引起 Si的非晶化 ,预先注入产生的损伤缺陷不利于 Si1 - x Cx 合金的形成 .与慢速退火工艺相比 ,快速热退火工艺有利于 Si1 - x Cx 合金的形成 .离子注入的 C原子在空间分布不均匀 ,退火过程中将形成应变不同的 Si1 - x-Cx 合金区域 .

Effect of Zn concentration on the microstructures and mechanical properties of extruded Mg-7Y-4Gd-0.4Zr alloys

Microstructures and mechanical properties of the Mg-7Y-4Gd-xZn-0.4Zr (x = 0.5, 1.5, 3, and 5 wt.%) alloys in the as-cast, as-extruded, and peak-aged conditions have been investigated by using optical microscopy, scanning electron microscope, X-ray diffraction, and transmission electron microscopy. It is found that the peak-aged Mg-7Y-4Gd-1.5Zn-0.4Zr alloys have the highest strength after aging at 220 A degrees C. The highest ultimate tensile strength and yield tensile strength are 418 and 320 MPa, respectively. The addition of 1.5 wt.% Zn to the based alloys results in a greater aging effect and better mechanical properties at both room and elevated temperatures. The improved mechanical properties are mainly ascribed to both a fine beta' phase and a long periodic stacking-ordered structure, which coexist together in the peak-aged alloys.