Enhancement of Low-field Magnetoresistance in Self-Assembled Epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 Composite Films via Polymer-Assisted Deposition

Polymer-assisted deposition method has been used to fabricate self-assembled epitaxial La(0.67)Ca(0.33)MnO(3):NiO and La(0.67)Ca(0.33)MnO(3):Co(3)O(4) films on LaAlO(3) substrates. Compared to pulsed-laser deposition method, polymer-assisted deposition provides a simpler and lower-cost approach to self-assembled composite films with enhanced low-field magnetoresistance effect. After the addition of NiO or Co(3)O(4), triangular NiO and tetrahedral Co(3)O(4) nanoparticles remain on the surface of La(0.67)Ca(0.33)MnO(3) films. This results in a dramatic increase in resistivity of the films from 0.0061 Ω•cm to 0.59 Ω•cm and 1.07 Ω•cm, and a decrease in metal-insulator transition temperature from 270 K to 180 K and 172 K by the addition of 10%-NiO and 10%-Co(3)O(4), respectively. Accordingly, the maximum absolute magnetoresistance value is improved from −44.6% to −59.1% and −52.7% by the addition of 10%-NiO and 10%-Co(3)O(4), respectively. The enhanced low-field magnetoresistance property is ascribed to the introduced insulating phase at the grain boundaries. The magnetism is found to be more suppressed for the La(0.67)Ca(0.33)MnO(3):Co(3)O(4) composite films than the La(0.67)Ca(0.33)MnO(3):NiO films, which can be attributed to the antiferromagnetic properties of the Co(3)O(4) phase. The solution-processed composite films show enhanced low-field magnetoresistance effect which are crucial in practical applications. We expect our polymer-assisted deposited films paving the pathway in the field of hole-doped perovskites with their intrinsic colossal magnetoresistance

Saddle Position-Based Method for Extraction of Depressions in Fengcong Areas by Using Digital Elevation Models

A karst depression is an important sign of the development stage of karst landforms. The morphological characteristics of depressions can help reflect the development and evolution process of such landforms. The accurate identification and extraction of depressions in Fengcong areas are the basis of this research on karst depressions. Previous studies on Fengcong depressions were primarily based on manual surveys, remote sensing image interpretation, and manual map plotting or GIS-based techniques. The extracted landform units of Fengcong depressions in these studies were not accurate and even inauthentic in certain cases. Thus, this work proposes a method for extracting Fengcong depressions in karst areas which is based on terrain saddle points and uses digital elevation models (DEMs). First, the surface morphology of the Fengcong karst area is analyzed. Second, saddles are detected from the intersection points, and spatial trend surfaces are generated by interpolating the elevations of these saddle points. The interface between pinnacles and depressions can be determined by the trend surface. We applied the method in a case Fengcong area of the Lijiang River in Guilin, China. Results showed that the proposed method successfully divided the positive terrain form of pinnacles and the negative terrain form of the depressions in the Fengcong karst area. A total of 188 surface depressions were extracted, whose average area was 0.14 km2 and polygonal depression density was 2.5 km2. Results also showed that most of the depressions were stable in terms of the morphological features of area and depth. A total of 94% of the depth measured less than 60 m, and the area was less than 0.5 km2. This proposed method can accurately determine the boundary of depressions and provide an important reference for quantitative research on the Fengcong depression terrain in karst landforms

Concentrations and isotopic variability of mercury in sulfide minerals from the Jinding Zn-Pb deposit, Southwest China

Mercury (Hg) isotopes have been proven as a useful tracer in understanding sources and biogeochemical processes of Hg in the environment. However, the use of this tracer has not yet been explored in economic geology. This paper investigates the concentrations and isotopic compositions of Hg in sulfide minerals from the Jinding deposit, the largest Zn-Pb deposit in China. Total mercury concentration (HgT) is highly variable: with the highest in sphalerite (472-1010 ng.g(-1)), intermediate concentrations in pyrite (195-342 ng.g(-1)) and the lowest in galena (65-310 ng.g-1). The variation was likely due to the fact that Hg2+ can more readily substitute for Zn2+ than for Fe2+ and Pb2+, but an influence of different parental fluids on the isotopic composition of the sulfide minerals cannot be excluded. An overall range of delta Hg-202 from -3.17 to -0.57 parts per thousand is observed in the sulfides. Samples from the early stage feature the enrichments of light Hg isotopes, with delta Hg-202 ranging from -3.17 to -1.59 parts per thousand, suggesting significant mass-dependent fractionation during the transport and/or deposition of Hg. However, the volatilization of aqueous Hg(0) during boiling of hydrothermal fluids was likely the most important process causing the observed fractionation. Relatively higher delta Hg-202 values (-1.84 to -0.57 parts per thousand) of the late stage samples indicate that the Hg was rarely fractionated from its sources. Additionally, small but significant mass-independent fractionations are measured for the deposit with Delta Hg-199 ranging from -0.06 to 0.10 parts per thousand, indicating that the Hg may have been derived from the sedimentary rocks of the Lanping Basin. Finally, we conclude that Hg isotopes have the potential to be a new tracer of sources of ore-forming materials, as well as pathways of fluid evolution in hydrothermal deposits. (C) 2017 Elsevier B.V. All rights reserved

Composite metallogenesis of sediment-hosted Pb-Zn-Ag-Cu base metal deposits in the Sanjiang Collisional Orogen, SW China, and its deep driving mechanisms

A great number of sediment-hosted Pb-Zn-Ag-Cu deposits occur in the Meso-Cenozoic sedimentary basins within the Sanjiang Tethyan orogeny, SW China, which compose a significant base metal metallogenic belt with an extension over 1000km along the northeastern margin of the Tibetan Plateau. For it is an important type in the continental collision-related deposit spectrum, further study upon these deposits is greatly helpful to understand and improve the theories of the continental collision metallogenesis and guide the exploration. Many studies suggest that these deposits are distinct from the SEDEX and MVT model in terms of ore controls, host rocks and other features, and that multiple sourced fluids associated with mineralization should have been driven by deep processes. However, it is intensively debated on the geotectonic settings of ore formation and spatial-temporal association with the collisional orogeny due to lack of highly resolved chronological data. Some studies indicate that they were resulted from composite mineralization, but these studies did not well document its mechanisms. A comprehensive study has thus been carried out on the geochronology, ore-forming fluids and metal sources, composite metallogenesis and mechanisms for the Pb-Zn-Ag and Cu polymetallic deposits in the Lanping and Changdu basins. The results show that the Cu deposits were mainly formed in 48 similar to 58Ma and the Pb-Zn deposits were formed in 28 similar to 33 Ma. Also, three types of composite mineralization have been recognized: 1) metamorphic fluids and basinal brines or meteoric water, represented by the Jinman-Liancheng Cu deposits; 2) basinal brine and meteoric water, represented by the Jinding deposit; and 3) basinal brine and magmatic fluid with an example of the Lanuoma Pb-Zn-Sb deposit. The Cu deposits happened synchronously with the main collisional compression of the India-Asian continental collision and metamorphic fluids were probably generated by subduction-caused high-pressure metamorphism. The Pb-Zn deposits were formed by basinal brine-dominated fluids driven by orogenic uplift as well as tectonic compression in the stage of the late collisional tectonic transform. Contemporaneous magmatism may have mainly played as heat sources or provided ore materials

In-situ analysis of major and trace elements in fluid inclusion and quartz: LA-ICP-MS method and applications to ore deposits.

LA-ICP-MS (Laser ablation-inductively coupled plasma-mass spectrometry) analysis of fluid inclusion is characterized by high precision, low detection limit and simultaneous measurement of multiple elements, which has remarkable advantages in revealing the specific mineralization processes. Based on using synthetic NaCl-H2O-Rb-Cs and NaCl-KC1-CaCl2-H2O-Rb-Cs fluid inclusions in quartz, a reliable analytical method of quantitatively determing major and trace elements in single fluid inclusion by LA-ICP-MS was established. In this method, external standard NIST610 and internal standard Na were used. The Na content was obtained from microthermometric measurement and calculated using the charge-balancing method. Analytical results show that the accuracy is within 16% and the precision is better than 7% RSD. In addition, combined with using the external standard NIST610 and a natural quartz standard, an analytical method for determing trace elements in quartz was also established. The accuracy for Li, Al and Ti is within 10% and the precision is better than 5% RSD. The above methods were applied to study the Cu and Mo mineralization mechanisms in the Wangjiazhuang Cu-Mo deposit in Luxi Block, eastern North China Craton. The results show that Cu is enriched in vapor-rich fluid inclusions, whereas Mo is concentrated in daughter mineral-bearing fluid inclusions, indicating that Cu was prone to be carried by vapor while Mo was likely carried by brine. This property is thus likely responsible for the depositional separation of Cu and Mo in the deposit. In addition, from the magmatic quartz to the ore-forming and then to the post-ore-forming quartz, the Ti contents decrease while the Al contents increase, suggesting the precipitation of Cu and Mo was also affected by the temperature and pH changes of the fluid

Lignin Distribution on Cell Wall Micro-Morphological Regions of Fibre in Developmental <i>Phyllostachys pubescens</i> Culms

Bamboo is a natural fibre reinforced composite with excellent performance which is, to a certain extent, an alternative to the shortage of wood resources. The heterogeneous distribution and molecular structure of lignin is one of the factors that determines its performance, and it is the key and most difficult component in the basic research into the chemistry of bamboo and in bamboo processing and utilization. In this study, the distribution of lignin components and lignin content in micro-morphological regions were measured in semi-quantitative level by age and radial location by means of visible-light microspectrophotometry (VLMS) coupled with the Wiesner and Maule reaction. There as guaiacyl lignin and syringyl lignin in the cell wall of the fibre. Lignin content of the secondary cell wall and cell corner increased at about 10 days, reached a maximum at 1 year, and then decreased gradually. From 17 days to 4 years, the lignin content of the secondary cell wall in the outer part of bamboo is higher than that in the middle part (which is, in turn, higher than that in the inner part of the bamboo). VLSM results of the micro-morphological regions showed that bamboo lignification developed by aging. Guaiacyl and syringl lignin units can be found in the cell wall of the fibre, parenchyma, and vessel. There was a difference in lignin content among different ages, different radial location, and different micro-morphological regions of the cell wall. The fibre walls were rich in guaiacyl lignin in the early stage of lignification and rich in syringyl units in the later stage of lignification. The guaiacyl and syringyl lignin deposition of bamboo green was earlier than that of the middle part of bamboo culm, and that of the middle part of bamboo culm was earlier than that of bamboo yellow. The single molecule lignin content of the thin layer is higher than that of thick layers, while the primary wall is higher than the secondary cell wall, showing that lignin deposition is consistent with the rules of cell wall formation. The obtained cytological information is helpful to understand the origin of the anisotropic, physical, mechanical, chemical, and machining properties of bamboo

Size Effects on Magnetic Properties of Ni0.5Zn0.5Fe2O4 Prepared by Sol-Gel Method

Ni0.5Zn0.5Fe2O4 particles with different particle sizes have been synthesized by sol-gel method. X-ray diffraction results show that all the samples are pure cubic spinel structure with their sizes ranging from 9 to 96 nm. The lattice constant significantly decreases with further increasing annealing temperature. The magnetic measurements show superparamagnetic nature below the particle size of 30 nm, while others show ferrimagnetic nature above the corresponding blocking temperature. The blocking temperature increases with the increase in particle size, which can be explained by Stoner-Wohlfarth theory. The saturation magnetization increases as the particle size increases, which can be explained by the cation redistribution on tetrahedral A and octahedral B sites and the domain wall motion. The variation of coercivity as a function of particle size is based on the domain structure

Genesis of the Jinding Zn-Pb deposit, northwest Yunnan Province, China: Constraints from rare earth elements and noble gas isotopes

The giant sediment-hosted finding zinc-lead deposit is located in the Lanping Basin, northwestern Yunnan Province, China. The genesis of the deposit has long been debated and the sources of the ore-forming fluids and metals are controversial. This study presents rare earth element (REE) and noble gas isotope data that constrain the origins of the ore fluids and the heat source driving the hydrothermal circulation. The early-stage sulfides are enriched in light REEs and have high Sigma REE values (30.8-94.8 ppm) and weakly negative Eu (delta Eu 0.85-0.89) and Ce anomalies (delta Ce 0.84-0.95), suggesting that the fluids were likely derived from dissolution of Upper Triassic marine carbonates with input of REEs from aluminosilicate rocks in the basin. In contrast, the late-stage sulfides have irregular REE patterns, generally low Sigma REE values (0.24-10.8 ppm) and positive Eu (delta Eu 1.22-10.9) and weakly negative Ce anomalies (delta Ce 0.53-0.90), which suggest that the ore-forming fluids interacted with evaporite minerals. The He-3/He-4 (0.01-0.04 R-a) and Ar-40/Ar-36 values (301-340) of the ore-forming fluids indicate crustal and atmospheric origins for these noble gases. These findings are in agreement with the published fluid inclusion microthermometry data and the results of H, O, C, S, Pb and Sr isotope studies. Our data, in combination with published results, support a two-stage hydrothermal mineralization model, involving early-stage basinal brines and late-stage meteoric water that acquired metals and heat from crustal sources. (C) 2017 Elsevier B.V. All rights reserved

Synthesis and characterization of self-assembled c-axis oriented Bi2Sr3Co2Oy thin films by the sol-gel method

Bi2Sr3Co2Oy thin films are prepared on SrTiO3 (100), (110) and (111) single crystal substrates using the sol–gel method. All the thin films are c-axis oriented regardless of the orientation of the substrate suggesting self-assembled c-axis orientation, and X-ray photoelectron spectroscopy results give evidence of coexistence of Co3+ and Co2+ ions in the derived films. Transmission electronic microscopy observations reveal that all samples are c-axis oriented with no obvious differences for different samples, and the c-axis lattice constant is determined as 15 Å suggesting the misfit structure. A phenomenological thermodynamic phase diagram for self-assembled c-axis orientation is established for misfit cobaltate-based films using chemical solution deposition. All samples behave like semiconductors due to the coexistence of Co3+/Co2+ ions, and the resistivity at 350 K is 47, 39 and 17 mΩ cm for the thin films on SrTiO3 (100), (110) and (111), respectively, whereas the Seebeck coefficient at 300 K is 97, 89 and 77 μV K−1. The successful attainment of Bi2Sr3Co2Oy thin films with self-assembled c-axis orientation will provide an effective prototype for investigation of growth mechanisms in complex oxide thin films with a misfit structure