Tensile Properties and Prediction Model of Recombinant Bamboo at Different Temperatures

The destruction of recombinant bamboo depends on many factors,and the complex ambient temperature is an important factor affecting its basic mechanical properties.To investigate the failure mechanism and stress–strain relationship of recombinant bamboo at different temperatures,eighteen tensile specimens of recombinant bamboo were tested.The results showed that with increasing ambient temperature,the typical failure modes of recombinant bamboo were flush fracture,toothed failure,and serrated failure.The ultimate tensile strength,ultimate strain and elastic modulus of recombinant bamboo decreased with increasing temperature,and the ultimate tensile stress decreased from 154.07 to 96.55 MPa,a decrease of 37.33%,and the ultimate strain decreased from 0.011 to 0.008,a decrease of 26.57%.Based on the Ramberg-Osgood model and the pseudo‒elastic design method,a predictive model was established for the tensile stress–strain relationship of recombinant bamboo considering the temperature level.The model can accurately evaluate the tensile stress–strain relationship of recombinant bamboo under different temperature conditions.

Experimental Study on the Creep Behavior of Recombinant Bamboo

The creep behavior of bamboo due to the complicated influences of environment and stress will lead to a sustained increase in deformation,which serious effects the service performance of structures.To investigate the creep behavior of recombinant bamboo,twenty-four recombinant bamboo specimens were tested under lasting compressive and tensile loads at different load levels.The typical failure modes of recombinant bamboo under a lasting load at a high load level were buckling failure and brittle fracturing due to creep compressive creep and tensile creep development,respectively.At a high load level,the creep deformation of recombinant bamboo initially develops unsteadily and increases rapidly until failure;at a low load level,creep deformation rapidly develops in the early stage and stabilizes in the middle and late stages.The load level has notable effects on the overall creep deformation and the proportion of creep deformation.The residual deformation of creep will generally increase and the recovery of creep will decrease with increasing load level.Based on the Burgers model,predictive models that can take the load levels into account were proposed to evaluate the compressive and tensile creep behaviors of recombinant bamboo.The proposed models can be used to accurately evaluate the strain-time behavior of recombinant bamboo.

Enhanced Thermoelectric Properties of Cu_(x)Se(1.75 ≤ x ≤ 2.10) during Phase Transitions

Coupling of a phase transition to electron and phonon transports provides extra degree of freedom to improve the thermoelectric performance, while the pertinent experimental and theoretical studies are still rare. Particularly,the impaction of chemical compositions and phase transition characters on the abnormal thermoelectric properties across phase transitions are largely unclear. Herein, by varying the Cu content x from 1.75 to 2.10, we systemically investigate the crystal structural evolution, phase transition features, and especially the thermoelectric properties during the phase transition for Cu_(x)Se. It is found that the addition of over-stoichiometry Cu in Cu_(x)Se could alter the phase transition characters and suppress the formation of Cu vacancies. The critical scatterings of phonons and electrons during phase transitions strongly enhance the Seebeck coefficient and diminish the thermal conductivity, leading to an ultrahigh dimensionless thermoelectric figure of merit of ~1.38 at 397 K in Cu_(2.10)Se.With the decreasing Cu content, the critical electron and phonon scattering behaviors are mitigated, and the corresponding thermoelectric performances are reduced. This work offers inspirations for understanding and tuning the thermoelectric transport properties during phase transitions.

Remarkable plasticity and softness of polymorphic InSe van der Waals crystals

Indium selenide(InSe)crystals are reported to show exceptional plasticity,a new property to twodimensional van der Waals(2D vdW)semiconductors.However,the correlation between plasticity and specific prototypes is unclear,and the understanding of detailed plastic deformation mechanisms is inadequate.Here three prototypes of InSe are predicted to be plastically deformable by calculation,and the plasticity of polymorphic crystals is verified by experiment.Moreover,distinct nanoindentation behaviors are seen on the cleavage and cross-section surfaces.The modulus and hardness of InSe are the lowest ones among a large variety of materials.The plastic deformation is further perceived from chemical interactions during the slip process.Particularly for the cross-layer slip,the initial In-Se bonds break while new In-In and Se-Se bonds are newly formed,maintaining a decent interaction strength.The remarkable plasticity and softness alongside the novel physical properties,endow InSe great promise for application in deformable and flexible electronics.

Room-temperature plastic inorganic semiconductors for flexible and deformable electronics

Flexible electronics ushers in a revolution to the electronics industry in the 21st century.Ideally,all components of a flexible electronic device including the functional component shall comply with the deformation to ensure the structural and functional integrity,imposing a pressing need for developing roomtemperature strain-tolerant semiconductors.To this end,there is a long-standing material dilemma:inorganic semiconductors are typically brittle at room temperature except for size-induced flexibility;by contrast,organic semiconductors are intrinsically soft and flexible but the electrical performance is poor.This is why the discovery of bulk plasticity in Ag2S at room temperature and ZnS in darkness is groundbreaking in solving this long-standing material dilemma between the mechanical deformability and the electrical performance.The present review summarizes the background knowledge and latest advances in the emerging field of plastic inorganic semiconductors.At the outset,we argue that the plasticity of inorganic semiconductors is vital to strain tolerance of electronic devices,which has not been adequately emphasized.The mechanisms of plasticity are illustrated from the perspective of chemical bonding and dislocations.Plastic inorganic materials,for example,ionic crystals(insulators),ZnS in darkness,and Ag2S,are discussed in detail in terms of their prominent mechanical properties and potential applications.We conclude the article with several key scientific and technological questions to address in the future study.

Cu2Se相变过程中热电效率增强的电子起源

热电材料可实现热能向电能的转换,是解决能源危机的潜在方式.目前热电材料的发展受限于较低的热电转换效率(可由热电优值zT评估),探索新型高zT热电材料或提升现有热电材料的z T值是亟待解决的重要课题.Cu2Se作为一种传统的超离子高z T热电材料一直备受关注.研究表明在其400 K附近的相变过程中,z T迅速提升了3倍.目前对这一变化的研究多限于晶体结构方面,而电子性质研究仅限于理论计算.本文利用高分辨角分辨光电子能谱技术,详细测量了相变过程其能带结构随温度的演变,揭示了相变过程中Cu2Se的电子结构的剧烈重组.作者利用光电子强度近似的模拟Cu2Se费米能级附近的电子态随温度的演化,并采用Mott模型来估算在相变过程中Seebeck系数的演化,再现了输运实验中Seebeck系数的提升.本研究表明电子结构在体系的热电性质中起了非常重要的作用,为理解和优化材料的热电性能提供了一种可能的方法.

Nano-scale compositional oscillation and phase intergrowth in Cu_(2)S_(0.5)Se_(0.5) and their role in thermal transport

Solid solution alloying is a promising strategy to establish high performance thermoelectrics.By alloying different elements,phase structures and phase compositions may vary accompanied by appearance of variety of interesting microstructures including mass fluctuation,lattice strain,nano-scale defects and spinodal decomposition,all of which may greatly influence the electrical and specifically the thermal transport of the material.In the present study,atomic structures of Cu_(2)S_(0.5)Se_(0.5) solid solution have been examined by using atom-resolved electron microscopy in order to investigate the structure-correlated physical insights for the abnormal thermal transport in this solid solution.Then the exceptional intergrowth nanostructures were observed.The solid solution consists of two high symmetrical phases,i.e.the hexagonal and cubic phase,which alternately intergrow to form highly oriented ultra-thin lamellae of nano or even,unit cell scales.The compositional oscillation in Se/S atomic ratio during alloying is responsible for the phase stability and intergrowth nanostructures.The unique binary phase intergrowth nanostructures make great contribution to the ultra-low lattice thermal conductivity comparable to glass and extremely short phonon mean free path of only 1.04Å,peculiar continuous hexagonal-to-cubic structural transformation without a critical transition temperature and its corresponding abnormal changes of thermal characters with temperatures.The present study further evokes the unlimited possibilities and potentials for tailoring nanostructures by alloying for improved thermoelectric performance.

Number mismatch between cations and anions as an indicator for low lattice thermal conductivity in chalcogenides

Thermal conductivity is one of the most fundamental properties of materials with the value being determined by nearly all-scale structural features and multiple physical processes.Rapidly judging material’s thermal conductivity is extremely important but challenging for the applications.The material genome paradigm offers a revolutionary way to efficiently screen and discover materials with designed properties by using accessible indicators.But such a performance indicator for thermal conductivity is quite difficult to propose due to the existence of multiple mechanisms and processes,especially for the materials with complex structures such as chalcogenides.In this study,the number mismatch between cations and anions is proposed as a practical performance indicator for lattice thermal conductivity in complex copper and silver chalcogenides,which can be used to explain the observed experimental data and find new low thermal conductivity materials.Such a number mismatch brings about rich phenomena to affect thermal conductivity including the complication of the unit cell and the creation of chemical hierarchy,point defects,rattling modes and lone-pair electrons.It is expected that this rich-connotation performance indicator can be also extended to other complex materials to discover designed thermal conductivities.