Electric Anisotropy and Two－dimensional Energy Band of Undoped and Heavily Doped Polyacetylene

ased on the known crystal data , we used the EHMACC(EHMO/CO) methodto calculate the twotlimensional energy band of both undoped and heavily iodine-doped polyacetylene (PA). The results show that (1 ) I-doping obviously reducesthe niagnitudes of Eg , Egi; (2) in the conducting process along the direction per-pendicular to PA chain , the P-type AO of iodine plays a very important role, i- e. ,the conducting bridge to transport the charge between the two neighbor PA chains.I-doping reniarkably increases σ_T value while the conducting process will reduce theratio magnitude of σ/σ. Therefore, heavily I-doping makes PA change fromsimeconductor to conductor which obviously has 2-D conductive ability.

Laboratory insights into the effects of methane hydrate on the anisotropic joint elastic-electrical properties in fractured sandstones

Fractured hydrate-bearing reservoirs show significantly anisotropic geophysical properties. The joint application of seismic and electromagnetic explorations is expected to accurately assess hydrate resources in the fractured reservoirs. However, the anisotropic joint elastic-electrical properties in such reservoirs that are the key to the successful application of the joint explorations, remain poorly understood. To obtain such knowledge, we designed and implemented dedicated laboratory experiments to study the anisotropic joint elastic-electrical properties in fractured artificial silica sandstones (with fracture density of about 6.2%, porosity of approximately 25.7%, and mean grainsize of 0.089 mm) with evolving methane hydrate. The experimental results showed that the anisotropic compressional wave velocities respectively increased and decreased with the forming and dissociating hydrate, and the variation in the increasing trend and the decreasing extent of the velocity perpendicular to the fractures were more significant than that parallel to the fractures, respectively. The experimental results also showed that the overall decreasing trend of the electrical conductivity parallel to the fractures was steeper than that perpendicular to the fractures during hydrate formation, and the general variations of the two conductivities with complex trend were similar during hydrate dissociation. The variations in the elastic and electrical anisotropic parameters with forming and dissociating hydrate were also found to be distinct. Interpretation of the experimental results suggested that the hydrate binding to the grains evolved to bridge the surfaces of fractures when saturation exceeded 10% during hydrate formation, and the bridging hydrate gradually evolved to floating in fractures during dissociation. The experimental results further showed that the anisotropic velocities and electrical conductivities were correlated with approximately consistent trends of different slopes during hydrate formation, and the joint elastic-electrical anisotropic parameters exhibited a sharp peak at the hydrate saturation of about 10%. The results suggested that the anisotropic joint properties can be employed not only to accurately estimate hydrate saturation but also possibly to identify hydrate distribution in the fractures.

Influence of anisotropy on the electrical conductivity and diffusion coefficient of dry K-feldspar： Implications of the mechanism of conduction

The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K–1223 K and 1.0 GPa–3.0 GPa in a frequency range of 10-1 Hz–106 Hz. The measured electrical conductivity along the ⊥ [001] axis direction decreases with increasing pressure, and the activation energy and activation volume of charge carriers are determined to be 1.04 ± 0.06 e V and 2.51 ± 0.19 cm~3/mole, respectively. The electrical conductivity of K-feldspar is highly anisotropic, and its value along the⊥ [001] axis is approximately three times higher than that along the ⊥ [100] axis. At 2.0 GPa, the diffusion coefficient of ionic potassium is obtained from the electrical conductivity data using the Nernst–Einstein equation. The measured electrical conductivity and calculated diffusion coefficient of potassium suggest that the main conduction mechanism is of ionic conduction, therefore the dominant charge carrier is transferred between normal lattice potassium positions and adjacent interstitial sites along the thermally activated electric field.

Anisotropic characteristics of electrical responses of fractured reservoir with multiple sets of fractures

In fractured reservoirs, the fractures not but also form the main flow channels which connect productivity of reservoirs. However, because of the only provide the storage space for hydrocarbons, the pores of the matrix, so fractures dominate the heterogeneity and randomness of the distribution of fractures, exploration and evaluation of fractured reservoirs is still one of the most difficult problems in the oil industry. In recent years, seismic anisotropy has been applied to the assessment of fractured formations, whereas electrical anisotropy which is more intense in fractured formations than seismic anisotropy has not been studied or used so extensively. In this study, fractured reservoir models which considered multiple sets of fractures with smooth and partly closed, rough surfaces were established based on the fractures and pore network, and the vertical and horizontal electrical resistivities were derived as a function of the matrix and fracture porosities according to Ohm＇s law. By using the anisotropic resistivity equations, variations of the electrical anisotropy of three types of fractured models under the conditions of free pressure and confining pressure were analyzed through the variations of the exerted pressure, matrix porosity, fracture aperture and formation water resistivity. The differences of the vertical and horizontal resistivities and the anisotropy between the connected and non-connected fractures were also analyzed. It is known from the simulated results that an increase of the confining pressure causes a decrease of electrical anisotropy because of the elasticity of the closed fractures and the decrease of the fracture aperture. For a fixed fracture porosity, the higher the matrix porosity, the weaker the electrical anisotropy in the rock formation.

Calculation of Constitutive Parameters from Electric and Magnetic Field Measurements in an Anisotropic Medium with a Triaxial Instrument

A hypothetical electric and magnetic induction tensor is considered in an anisotropic medium. The sources are magnetic dipoles. In such a medium, constitute parameters can be calculated by combining electric and magnetic field measurements. Constitutive parameters are not a scalar in this case. They are tensors, so parameters have at least both horizontal and vertical components in a uniaxial medium. These calculated parameters from the field measurement are horizontal and vertical conductivity, permittivity, and magnetic permeability. Operating frequency range is also quite large. It is up to 4 GHz. A hypothetical instrument should measure gradient fields both electric and magnetic types as well.

Optical and electronic anisotropy of a 2D semiconductor SiP

Two-dimensional anisotropic materials have been widely concerned by researchers because of their great application potential in the field of polarized detector devices and optical elements,which is a very important and popular research direction at present.As a IV-V two-dimensional material,silicon phosphide(SiP)has obvious in-plane anisotropy and exhibits excellent optical and electrical anisotropy properties.Herein,the optical anisotropy of SiP is studied by spectrometric ellipsometry measurements and polarization-resolved optical microscopy,and its electrical anisotropy is tested by SiP-based field-effect transistor.In addition,the normal and anisotropic photoelectric performance of SiP is shown by fabricating a photodetector and measuring it.In various measurements,SiP exhibits obvious anisotropy and good photoelectric performance.This work provides basic optical,electrical,and photoelectric performance information of SiP,and lays a foundation for further study of SiP and applications of SiP-based devices.

Boosting in-plane anisotropy by periodic phase engineering in two-dimensional VO_(2) single crystals

In-plane anisotropy(IPA)due to asymmetry in lattice structures provides an additional parameter for the precise tuning of characteristic polarization-dependent properties in two-dimensional(2D)materials,but the narrow range within which such method can modulate properties hinders significant development of related devices.Herein we present a novel periodic phase engineering strategy that can remarkably enhance the intrinsic IPA obtainable from minor variations in asymmetric structures.By introducing alternant monoclinic and rutile phases in 2D VO_(2)single crystals through the regulation of interfacial thermal strain,the IPA in electrical conductivity can be reversibly modulated in a range spanning two orders of magnitude,reaching an unprecedented IPA of 113.Such an intriguing local phase engineering in 2D materials can be well depicted and predicted by a theoretical model consisting of phase transformation,thermal expansion,and friction force at the interface,creating a frame-work applicable to other 2D materials.Ultimately,the considerable adjustability and reversibility of the presented strategy provide opportunities for future polarization-dependent photoelectric and optoelectronic devices.