Researching | WLXB Volume 69 Issue 11,2020

Shi-Jian Zhang, Xiao Yu, Hao-Wen Zhong, Guo-Ying Liang, Mo-Fei Xu, Nan Zhang, Jian-Hui Ren, Shi-Cheng Kuang, Sha Yan, Efimovich Remnev Gennady, and Xiao-Yun Le

Short-pulse length and high-power density, intense pulsed ion beam (IPIB) has been widely studied in material processing during past decades. Ablation effect plays a great role in the interaction between IPIB and material and may affect the energy deposition of IPIB, thus further influencing the beam application and di Short-pulse length and high-power density, intense pulsed ion beam (IPIB) has been widely studied in material processing during past decades. Ablation effect plays a great role in the interaction between IPIB and material and may affect the energy deposition of IPIB, thus further influencing the beam application and diagnostics. Therefore, the investigation of ablation effect on energy deposition of IPIB in the irradiated material is of great significance for its applications and diagnostic techniques. In this work, experiments on the IPIB irradiation are carried out on the BIPPAB-450 accelerator at Beihang University. Its maximum accelerating voltage is 450 kV, peak current density is 150 A/cm², energy density is 1.5–1.8 J/cm² and pulse duration (FWHM) is 80 ns. Polymer materials which have low thermal conductivity, low decomposition temperature and thus yield to ablation under low beam density, such as polycarbonate (PC), polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA), are chosen in the present research. The 304 stainless steel is used for calorimetric beam diagnostics and comparative analysis. Energy deposition in polymer material and 304 stainless steel are obtained by high infrared imaging diagnostics. It is revealed that the distributions of energy deposition in these two kinds of materials differ from each other obviously. The highest energy density deposited in the 304 stainless steel appears in the center of the irradiated area where focused is the beam with a higher energy density. However, the central energy density in polymer material turns out to be lower than the surrounding area, indicating that a large portion of the ion beam is prevented from reaching the target. Meanwhile, the simulation based on the finite element method is carried out for the thermal filed distribution and evolution under the IPIB irradiation. The simulation result indicates that the strong ablation can be generated on the target surface since the highest temperature caused by IPIB irradiation is much higher than its decomposition temperature. According to the results of experiments and simulation, the polymer material can start to be ablated at the initial stage of IPIB irradiation which will consume partial energy and the products of ablation may act as shielding to block the energy deposition in the same pulse..

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 115202-1 (2020)

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Influence of screen gird aperture diameter in outer region on performance of dual-mode ion thruster

Yi-De Zhao, Juan Li, Zong-Hai Wu, Yong-Jie Huang, Jian-Peng Li, and Tian-Ping Zhang

To eliminate the erosion in the apertures at the edge of the decelerate grid of a dual-mode ion thruster three-grid optical system, a new method of reducing the diameter of the apertures in the outer region of the screen grid is proposed. In order to investigate the method of influencing the discharge loss and the unif To eliminate the erosion in the apertures at the edge of the decelerate grid of a dual-mode ion thruster three-grid optical system, a new method of reducing the diameter of the apertures in the outer region of the screen grid is proposed. In order to investigate the method of influencing the discharge loss and the uniformity of the beam current density and also reducing the aperture erosion region and erosion rate of the decelerate grid, two kinds of three-grid optical systems are designed and fabricated with the same material and physical parameters except the diameter of the apertures in the outer region of the screen grid. The first kind is that the diameter of the aperture in the outer region of the screen grid is equal to that in middle region of the screen grid, it is designated as the same aperture diameter grid optical system. The second kind of three-grid optical system is that the diameter of screen apertures whose center distance from the center of grid is larger than 0.95 times the beam radius, is reduced by 26% and therefore the physical transparency of optical system is reduced by 8.8%, it is designated as the small aperture diameter grid optical system. The comparison between the same aperture diameter grid optical system and small aperture diameter grid optical system is performed by assembling them into a 30-cm-diameter dual-mode ion thruster, and the ion thruster performance test, beam flatness test and 600-h-endurance test are conducted in the two typical operation modes, namely the low thrust-high specific impulse mode and large thrust-high power mode. A comparison of small aperture diameter grid optical system with the same aperture diameter grid optical system shows that the discharge loss of the 30-cm dual-mode ion thruster in the low thrust-high specific impulse mode and large thrust-high power mode are reduced by 10% and 21% respectively, the beam flatness is decreased by 3% and 10% respectively, the number of rows of the apertures which are sputtered by beam ions at the edge of the decelerate grid is reduced from 5 to 1. In addition, the erosion rate is significantly reduced and the erosion phenomenon disappears after 900-h-long-duration operation. These results signify that reducing the screen grid aperture diameter in the outer region is an effective method to eliminate aperture erosion at the edge of the decelerate grid of a dual-mode ion thruster three-grid optical system and that this method will not reduce the efficiency of the thruster, but cause the beam current uniformity to worsen..

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 115203-1 (2020)

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Numerical study on discharge characteristics in ultra-high frequency band modulated by pulses with electrodes covered by barriers

Shu-Han Gao, Xu-Cheng Wang, and Yuan-Tao Zhang

Pulse-modulated discharge is an effective way to improve the stability of radio-frequency (rf) discharges. Previous studies have shown that with the power frequency increasing to the ultra-high frequency (UHF) band, the introduction of pulse modulation in rf discharges will bring about new discharge behaviors. In this

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 115204-1 (2020)

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Molecular dynamics simulation of effect of cooling rate on the microstructures and deformation behaviors in metallic glasses

Bian Zhou, and Liang Yang

Since the discovery of the first metallic glass (MG) in 1960, vast efforts have been devoted to the understanding of the structural mechanisms of unique properties, in particular, mechanical properties in MGs, which is helpful for the applications of such novel alloys. As is well known, the cooling rate during the quen Since the discovery of the first metallic glass (MG) in 1960, vast efforts have been devoted to the understanding of the structural mechanisms of unique properties, in particular, mechanical properties in MGs, which is helpful for the applications of such novel alloys. As is well known, the cooling rate during the quenching as well as the sample size, significantly affects the mechanical properties in MGs. In order to study the effect of cooling rate on microstructure and deformation behavior in MG by excluding the size effect, Zr₄₈Cu₄₅Al₇ ternary composition with good glass-forming ability is selected as a research prototype in this work. The classical molecular dynamics simulation is utilized to construct four structural MG models with the same size under different cooling rates, and the uniaxial compressive deformation for each model is also simulated. It is found that an MG model prepared at a lower cooling rate has a higher yield strength and is more likely to form shear bands that lead the strain to be localized, resulting in a lower plasticity. The Voronoi tessellation, together with atomic packing efficiency and free volume algorithms that have been designed by ourselves, is used to analyze the four as-constructed models and high-temperature liquid model. It is found that the as-constructed model, which is prepared by quenching metallic melt at a higher cooling rate, can preserve more structural characteristics of the high-temperature liquid. In other words, the higher cooling rate leads to more clusters with relatively low five-fold symmetry, loose atomic packing and large fraction of free volumes in MG. By calculating the distribution of the free volumes, a new computational approach to detecting liquid-like regions in MG models is adopted. It is found that there are more liquid-like regions in the as-constructed model which is prepared by quenching metallic melt at a relatively high cooling rate. This should be the structural origin of the effect of cooling rate on the deformation behavior, in particular, the yield strength and the plasticity. This work provides an understanding of how the cooling rate during quenching affects the microstructure and deformation behavior, and will shed light on the development of new MGs with relatively large plasticity..

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 116101-1 (2020)

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Effect of interstitial

${\left\langle {100} \right\rangle }$

dislocation loop on expansion of micro-crack in body centered cubic iron investigated by molecular dynamics method

Jin-Jie Liang, Ning Gao, and Yu-Hong Li

The interactions between the energetic particles and atoms in materials would result in the atomic displacements and the associated radiation defects. The interstitial dislocation loop, as one of the primary radiation defects, is formed by the clustering of the supersaturated self-interstitial atoms from the displaceme The interactions between the energetic particles and atoms in materials would result in the atomic displacements and the associated radiation defects. The interstitial dislocation loop, as one of the primary radiation defects, is formed by the clustering of the supersaturated self-interstitial atoms from the displacement damages in body centered cubic (bcc) iron based materials. The radiation hardening, embrittlement, swelling, creep, etc. are generally related to these loops and their interactions with other defects. In addition, the irradiation would also result in the formation of the micro-cracks from the surface of the materials and also from the interface of grains, precipitates, and gas-bubbles inside the materials, which would result in the irradiation assisted stress corrosion crack (IASCC). Therefore, to understand the interaction between interstitial dislocation loop and micro-crack under the irradiation, is one of key steps to understand the underlying mechanism of IASCC. In this work, the interaction between interstitial dislocation loop and micro-crack is simulated by molecular dynamics method on an atomic scale. The distance, relative position between them and radius of dislocation loop, as the main factors affecting their interactions, are studied to explore the underlying reason for inducing the micro-crack to expand on the slip plane. The simulation results indicate that when the interaction between them dominates the whole process with the distance between them within the critical value, the dislocation network containing the

$ \langle 100 \rangle $

and 1/2

$ \langle 111 \rangle $

segments, would interact with the crack tip to inhibit the crack from expanding through the pinning effect. When the size of loop is different, the pining effect would be available only when the interaction between loop core and crack tip dominates with the distance between them within the critical value. All these results provide new understanding for further exploring the IASCC under irradiation..

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 116102-1 (2020)

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First-principles calculations of stabilities and physical properties of ternary niobium borocarbides and tantalum borocarbides

Qian-Ku Hu, Shuang-Hong Qin, Qing-Hua Wu, Dan-Dan Li, Bin Zhang, Wen-Feng Yuan, Li-Bo Wang, and Ai-Guo Zhou

Transition-metal light-element compounds are potential candidates for hard materials. In the past, most of studies focused on the binary transition metal borides, carbides and nitrides, while the researches of ternary phases are relatively rare. In this paper, the structure units of the known Nb3B3C and Nb4B3C2 phases

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 116201-1 (2020)

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Molecular dynamics simulation of shock-induced isostructural phase transition in single crystal Ce

Min-Jie Diwu, and Xiao-Mian Hu

Cerium (Ce), a rare earth metal, undergoes a significant (14%-17%) and discontinuous volume shrinkage when subjected to ~0.7 GPa compression at ambient temperature: there happens a first-order isostructural phase transition fromγ-Ce phase to α-Ce phase (these two phases are both face-centered-cubic (fcc) phase). Becaus Cerium (Ce), a rare earth metal, undergoes a significant (14%-17%) and discontinuous volume shrinkage when subjected to ~0.7 GPa compression at ambient temperature: there happens a first-order isostructural phase transition fromγ-Ce phase to α-Ce phase (these two phases are both face-centered-cubic (fcc) phase). Because of the α→ γ transition in Ce under shock compression, the shock front in cerium exhibits a 3-wave configuration: elastic precursor, plastic shock wave in γ-Ce, and phase transition wave corresponding to the γ→ α transition according to the experimental observation. In this paper, a recently developed embedded-atom-method (EAM) potential for fcc Ce is employed in the large-scale molecular dynamics simulations of shock loading onto single crystal Ce to study its dynamic behavior, especially the shock-induced α→ γ phase transition, and the orientation dependence with [001], [011] and [111] shock loading. The simulation results show single-wave or multi-wave configuration for shock wave profiles. Under the shock loading along the [001] or [011] crystallographic orientation, the shock wave possesses a 2-wave structure: an elastic precursor and a phase transition wave, while under shock loading along the [111] crystallographic orientation, the obtained shock wave shows a 3-wave profile as observed experimentally. Thus the shock wave structure is obviously dependent on loading orientation. The Hugoniot data obtained in MD simulation show good agreement with the experimental results. The shock loading MD simulation shows lower phase transition pressure than hydrostatic loading, indicating an accelerant role of the deviatoric stress played in the shock inducedγ→ α phase transition in Ce. The local lattice structure before and after shocked are recognized with polyhedral template matching and confirmed with radial distribution functions. Under the [011] and [111] loading, the lattice structure maintains the fcc before and after the shocks, and experiences a collapse during the last shock (the second shock for the [011] loading and the third shock for the [111] loading). The lattice structure also maintains fcc before and after the first shock for the [001] loading, while after the second shock the structure type is considered to be body-centered-tetragonal (bct) which is a meta-stable structure resulting from the used EAM potential for Ce. The fcc lattice rotation after shock is observed in the [011] and [111] loading after the phase transition, while no re-orientation occurs in the [001] loading..

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 116202-1 (2020)

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Effect of straining flow on growth of columnar crystal in ternary undercooled melt

Hai-Long Fan, and Ming-Wen Chen

As an important microstructure, columnar crystal growth technology, especially the growth technology of single columnar crystal plays an important role in improving the performances of semiconductor, optical devices and other related products. In many practical applications, because the alloy is composed of multi-compo As an important microstructure, columnar crystal growth technology, especially the growth technology of single columnar crystal plays an important role in improving the performances of semiconductor, optical devices and other related products. In many practical applications, because the alloy is composed of multi-component and there is inevitably flow in the melt, it is necessary to study the growth of columnar crystals in multi-component melt with flow separately. The growth of columnar crystal in a ternary undercooled melt subjected to straining flow under non-isothermal conditions is studied, and the approximate analytical expression for growth morphology of columnar crystal is given by using asymptotic method. It can be seen from the expression that straining flow is an important reason for irregular columnar crystal. When analyzing the effect of straining flow on the growth of columnar crystal in ternary melt, it is found that the incoming flow accelerates the growth velocity of the interface, while the outgoing straining flow reduces the growth velocity of the interface, namely, the straining flow makes the interface of columnar crystal deformed. At the same time, it is found that the interface deformation becomes more intense with the increase of flow velocity. The above conclusion can also be applied to the effect of straining flow on the interface morphology of columnar crystal in pure melt and binary melt. The comparison of the effects of straining flow on the interface of columnar crystal among pure melt, binary melt and ternary melt, shows that the interface morphology of columnar crystal in dilute alloy melt is more affected by straining flow than in the pure melt, but the more components are more easily affected by flow. However, the number of components in melt is not a decisive factor for the change of interface morphology of the columnar crystal, but the constitutional undercooling is an important factor for determining the interface morphology of multicomponent alloy. According to the conclusion of this paper, the influence of straining flow on the interface morphology of columnar crystal growth can be quantitatively predicted, which provides the necessary theoretical guidance in accurately controlling the interface morphology in the future..

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 116401-1 (2020)

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Theoretical study on Schottky regulation of WSe₂/graphene heterostructure doped with nonmetallic elements

Hao-Hao Ma, Xian-Bin Zhang, Xu-Yan Wei, and Jia-Meng Cao

In order to effectively control the type and height of Schottky barrier, it is crucial to appropriately select the material and method of controlling the type and height of the Schottky barrier effectively. Two-dimensional materials exhibit massive potential in research and development due to their unique electrical, o In order to effectively control the type and height of Schottky barrier, it is crucial to appropriately select the material and method of controlling the type and height of the Schottky barrier effectively. Two-dimensional materials exhibit massive potential in research and development due to their unique electrical, optical, thermal and mechanical properties. Graphene is a two-dimensional material found earliest, which has many excellent properties, such as high carrier mobility and large surface area. However, single-layered graphene has a zero band gap, which limits its response in electronic devices. Unlike the graphene, the transition metal sulfides have various band structures and chemical compositions, which greatly compensate for the defect of zero gap in graphene. From among many two-dimensional transition metal sulfides, we choose WSe₂. The reason is that the single-layered WSe₂ possesses the photoelectric excellent performance, band gap that can meet the majority of requirements in electronic and photoelectric devices, and transport properties that can be adjusted to p-type or bipolar which is first found in semiconductor materials. And compared with metal, the graphene at room temperature has superior properties such as high electron mobility, resistivity of 10^-6 Ω·m lower than copper and silver, coefficient of thermal conductivity 5300 W/(m·K) large than 10 times that of copper, aluminum and other metal, and hardness exceeding the diamond, fracture strength up to 100 times more than that of iron and steel. The Two-dimensional semiconductors along with semimetallic graphene are seen as the basic building blocks for a new generation of nanoelectronic devices, in this sense, the artificially designed transition metal sulfide heterostructure is a promising option for ultrathin photodetectors. At present, most researchers focus on the control of the type and height of Schottky via heterojunction doped metallic element. However, there are few Schottky that are doped by nonmentallic element. Therefore, our work provides the interaction between WSe₂ and graphene, which are described by the first principles effectively. The results show that there is the van der Waals interaction between the interface of WSe₂ and that of graphene, and thus forming a stable structure. Through the analysis of energy band, it is found that the semiconductor properties of WSe₂ are changed by the coupling between WSe₂ and graphene, making the WSe₂ transform from direct band gap into indirect band gap semiconductor. Furthermore, the total density of states and corresponding partial density of states of WSe₂/graphene heterostructure are investigated, and the results show that the valence band is composed of hybrid orbitals of W 5d and Se 4p, whereas the conduction band is comprised of W 5d and C 2p orbitals, the orbital hybridization between W 5d and Se 4p will cause the photo generated electrons to transfer easily from the internal W atoms to the external Se atoms, thereby forming a build-in internal electric field from graphene to WSe₂. Finally, for ascertaining the effect of doping WSe₂ with nonmetallic elements, the WSe₂/graphene Schottky is investigated by using the plane-wave ultrasoft pseudo potentials in detail. Besides, the lattice mismatch rate and lattice mismatch can prove the rationality of doping WSe₂ by non-metallicelement. The stability of the combination between the doped WSe₂ and graphene is demonstrated by the interface binding energy. The influence of nonmetallic atoms on WSe₂ is analyzed before investigating the heterojunction of the doped WSe₂ and graphene. The results show that the band gap of WSe₂ doped by O atoms changes from 1.62 to 1.66 eV and the leading band moves upward by 0.04 eV. This indicates that O atom doping has little effect on the band gap of WSe₂. When WSe₂ is doped with N and B atoms, the impurity energy level appears near the Fermi level of WSe₂, which results in the band gap being zero, and then it presents severe metallization. This is due to the Fermi level of WSe₂ shifting. When the C atom is doped, the impurity level appears at the bottom of the guide band of WSe₂, and the band gap is 0.78 eV. Furthermore, we analyze the effect of doping on heterojunction. In the W₉Se₁₇O₁/graphene heterojunction, the Schottky barrier height of n-type and p-type are 0.77 eV and 0.79 eV respectively. It shows that the heterojunction type transforms form p-type into n-type, whose Schottky barrier height is reduced effectively. Due to the W₉Se₁₇N₁ as well as W₉Se₁₇B₁ with metallic properties combining with graphene, the Fermi energy level of graphene is shifted, its Dirac point is located above the Fermi energy level and its conduction band has a filling energy level. When doped with N and B atoms, WSe₂/graphene belongs to the type of ohmic contact. When W₉Se₁₇C₁ contacts the graphene, the graphene Dirac point is on the Fermi surface, and the Fermi energy level of W₉Se₁₇C₁ is shifted by 0.59 eV. And then, the height of Schottky barrier of type-n for the heterojunction is 0.14 eV, the height of type-p is 0.59 eV and overall type of heterojunction is type-n. Therefore, by doping WSe₂ with O, N, C and B, the WSe₂/graphene Schottky type and barrier height can be adjusted. These will provide guidance for designing and manufacturing the 2D FET..

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 117101-1 (2020)

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Memristive and magnetoresistance effects of SnSe₂

Bin He, Xiong He, Guo-Qiang Liu, Can Zhu, Jia-Fu Wang, and Zhi-Gang Sun

Memristor and magnetoresistance (MR) are widely used in the field of information storage. In recent years, SnSe2, as an information storage material with both memristor and MR effects, has received a lot of attention of the researchers. It is of great significance to further explore its electrical transport mechanism. Memristor and magnetoresistance (MR) are widely used in the field of information storage. In recent years, SnSe₂, as an information storage material with both memristor and MR effects, has received a lot of attention of the researchers. It is of great significance to further explore its electrical transport mechanism. In this paper, the high-purity bulk SnSe₂ samples are prepared by melting method together with spark plasma sintering. The V-I curves are measured under different temperatures and magnetic fields. The memristive and MR effect of SnSe₂ are systematically investigated. After the memristive characteristics are excluded from interfacial junction effect, phase transition and conductive wire channels, the memristive effect at different temperatures is attributed to the space charge limiting current effect under defect control. Under low electric field conditions, the internal carrier concentration of material is much higher than the injected carrier concentration and the V-I curve obeys ohmic conduction. When the voltage increases to the switching voltage V_on, the internal defects of the material are filled with the injected carriers as the transport time of the injected carrier is less than the dielectric relaxation time, and the V-I curves deviate from ohmic conductivity. When the voltage reaches the transition voltage V_TFL, the injected carrier increases exponentially, and the V-I curve presents negative differential phenomenon. Finally, the space charge inside the material will limit the further injection of external carriers, and the V-I curve follows the Child law. As the temperature decreases to 10 K, the memristive phenomenon weakens because a large number of defects for accepting the injected carriers are reduced due to the decrease of impurity ionization at low temperatures. At the same time, the sample exhibits a large negative MR at 10 K and 100 K. When impurity scattering predominates, the electrons will be subjected to multiple scattering by the impurities, resulting in localization of carriers. The negative MR effect is related to the inhibition of the carrier localization by the magnetic field. In our work, a large negative MR of about –37% at 0.6 T and 10 K are obtained, which is likely to originate from the disordered distribution of Se vacancy in the material. With the increase of temperature, the scattering mechanism gradually evolves from the impurity scattering into the lattice scattering, and the negative MR effect gradually develops into the positive MR effect..

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 117301-1 (2020)

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Preparation and properties of spodumene/silicon carbide composite ceramic materials

Yuan-Yuan Lu, Gui-Hua Lu, Heng-Wei Zhou, and Yi-Neng Huang

Silicon carbide (SiC) is widely used due to the lower coefficient of thermal expansion (CTE), high thermal conductivity and excellent mechanical properties. However, the self-diffusion coefficient of SiC relative to that of oxide ceramics is very low, it is difficult to sinter at lower temperature. The β-spodumene has Silicon carbide (SiC) is widely used due to the lower coefficient of thermal expansion (CTE), high thermal conductivity and excellent mechanical properties. However, the self-diffusion coefficient of SiC relative to that of oxide ceramics is very low, it is difficult to sinter at lower temperature. The β-spodumene has ultra low or even negative thermal expansion coefficient combined with good thermal and chemical durability, which melts at 1423 ℃. Accordingly, the present study focuses on the use of β-spodumene as a flux at lower sintering temperature and the preparation of lower CET composite ceramics. The effects of spodumene on the sintering behavior, phase relations, thermal expansion and mechanical properties of spodumene/silicon carbide composites are discussed. A high pure β-spodumene LiAlSi₂O₆ compound with nearly zero thermal expansion coefficient is synthesized via solid phase sintering. Spodumene/silicon carbide composites are fabricated by the adding 25, 30, 35 and 40 mass% synthesized β-spodumene powder to 75, 70, 65 and 60 mass% α-SiC matrix, respectively. Both β-spodumene and SiC are fabricated by conventional pressureless liquid sintering technique, and the batches are uniaxially pressed into discs and rectangular bars, then sintered at 1550 ℃ for 2 h in an Ar atmosphere. The results show that the SiC and β-spodumene do not react during sintering, and the β-spodumene changes from tetragonal phase into hexagonal phase, the cell volume has a considerable shrinkage. A certain amount of liquid phase can help to enhance the density, improve Young’s modulus and promote the sintering behavior of SiC. When the feedstock contains 35% β-spodumene, the Young’s modulus reaches to (204.2 ± 0.5) GPa. Excess porosity is formed when liquid phase is too much during sintering, The Young's modulus of the sample 40SP is (119.6 ± 0.5) GPa. It is determined that the Young’s modulus of these materials are affected by porosity and internal microcracks. This study indicates that the content of β-spodumene and porosity are the dominant factors to control the CET of composites, but the porosity has a stronger effect. Besides, the microcracks, which are formed by the interaction of various internal stresses, are also an impotant factor. The materials with nearly zero thermal expansion are developed in a lower temperature range from –150 ℃ to 25 ℃, the spodumene content in the most stable composite reaches 40 mass%, and the CET of composite is close to that of Si (α_{25 ℃} = 2.59 × 10^–6 ℃^–1) in a temperature range of 25–480 ℃. .

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 117701-1 (2020)

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Theoretical study of photovoltaic performance for inverted halide perovskite solar cells

Ao Zhang, Chun-Xiu Zhang, Yun-Lin Chen, Chun-Mei Zhang, and Tao Meng

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 118801-1 (2020)

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Modification of method of sampling radiation source particle in spherical geometry

Yu-Pei Xu, and Shu Li

Sampling of radiation source particles is important for obtaining a correct result in the thermal radiative transfer simulation with implicit Monte Carlo. When conducting the implicit Monte Carlo simulation of spherical geometry, temperature in a cell (a spherical shell) is generally treated as a spatially independent Sampling of radiation source particles is important for obtaining a correct result in the thermal radiative transfer simulation with implicit Monte Carlo. When conducting the implicit Monte Carlo simulation of spherical geometry, temperature in a cell (a spherical shell) is generally treated as a spatially independent value. That means that the particles of radiative source are uniformly distributed in a spherical shell. In some cases where the gradient of temperature inside a cell is relatively small, the treatment does not cause too many errors. However, when the opacity of material becomes large enough or the spherical shell becomes thick enough, the temperature of thermal wave head will change sharply and there will be a great temperature gradient even in a single spherical shell. The treatment will make the thermal radiation propagate much faster than the practical one, which is unacceptable in physics. We investigate the physical and numerical reasons for this violation, finding that the simulation results strongly rely on the separation of cell and that the thermal wave propagates faster with the cell number decreasing. In order to yield an accurate result, the cell number has to increase up to a large enough value. Unfortunately, more cells need more particles to reduce the numerical variance, and more particles will cost more computation time and thus causing the simulation efficiency to lower. In our work, temperature is not treated as a constant in space any more. Instead, it is treated as a linear function in a cell. Based on a new temperature function and radiative energy density distribution, a probability density distribution function of emitting position of radiation source particle in spherical geometry is obtained. Then two new spatial sampling methods are proposed and the sampling procedures of radiation source particle are designed. To verify our new sampling methods, we test several typical thermal radiative problems and compare the result with a reference solution. Numerical experiments show that both two new sampling methods can correct the errors of thermal radiative propagation speed and overcome the difficulty that simulation result is strongly dependent on cell number. In addition, both new sampling methods can obtain an accurate result even with less cells and less particles, which can saves plenty of computation time and improves the simulation efficiency..

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 119501-1 (2020)

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Illumination and temperature analysis for CE-5 candidate landing site Mons Rümker

Zhen Zhong, Teng Zhang, Jie Zhang, and Shi-Guo Chen

The forthcoming lunar exploration of Chang’e-5 (CE-5) mission will be the first sampling return project of China. The actual drilling needs the information about real-time illumination and corresponding temperature. To give a support for the project, in this paper the SPICE software system is first used to calculate th

Acta Physica Sinica

Publication Date: Jan. 01, 1900
Vol. 69, Issue 11, 119601-1 (2020)

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