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Robert W Carpick - One of the best experts on this subject based on the ideXlab platform.
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memory distance for interfacial Chemical Bond induced friction at the nanoscale
ACS Nano, 2019Co-Authors: Kaiwen Tian, Nitya Nand Gosvami, D L Goldsby, Izabela Szlufarska, Robert W CarpickAbstract:Macroscale rate and state friction (RSF) laws include a memory distance, Dc, which is considered to be the distance required for a population of frictional contacts to renew itself via slip, counte...
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load and time dependence of interfacial Chemical Bond induced friction at the nanoscale
Physical Review Letters, 2017Co-Authors: Kaiwen Tian, Nitya Nand Gosvami, D L Goldsby, Yun Liu, Izabela Szlufarska, Robert W CarpickAbstract:Rate and state friction (RSF) laws are widely used empirical relationships that describe the macroscale frictional behavior of a broad range of materials, including rocks found in the seismogenic zone of Earth's crust. A fundamental aspect of the RSF laws is frictional ``aging,'' where friction increases with the time of stationary contact due to asperity creep and/or interfacial strengthening. Recent atomic force microscope (AFM) experiments and simulations found that nanoscale silica contacts exhibit aging due to the progressive formation of interfacial Chemical Bonds. The role of normal load (and, thus, normal stress) on this interfacial Chemical Bond-induced (ICBI) friction is predicted to be significant but has not been examined experimentally. Here, we show using AFM that, for nanoscale ICBI friction of silica-silica interfaces, aging (the difference between the maximum static friction and the kinetic friction) increases approximately linearly with the product of the normal load and the log of the hold time. This behavior is attributed to the approximately linear dependence of the contact area on the load in the positive load regime before significant wear occurs, as inferred from sliding friction measurements. This implies that the average pressure, and thus the average Bond formation rate, is load independent within the accessible load range. We also consider a more accurate nonlinear model for the contact area, from which we extract the activation volume and the average stress-free energy barrier to the aging process. Our work provides an approach for studying the load and time dependence of contact aging at the nanoscale and further establishes RSF laws for nanoscale asperity contacts.
Kaiwen Tian - One of the best experts on this subject based on the ideXlab platform.
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memory distance for interfacial Chemical Bond induced friction at the nanoscale
ACS Nano, 2019Co-Authors: Kaiwen Tian, Nitya Nand Gosvami, D L Goldsby, Izabela Szlufarska, Robert W CarpickAbstract:Macroscale rate and state friction (RSF) laws include a memory distance, Dc, which is considered to be the distance required for a population of frictional contacts to renew itself via slip, counte...
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load and time dependence of interfacial Chemical Bond induced friction at the nanoscale
Physical Review Letters, 2017Co-Authors: Kaiwen Tian, Nitya Nand Gosvami, D L Goldsby, Yun Liu, Izabela Szlufarska, Robert W CarpickAbstract:Rate and state friction (RSF) laws are widely used empirical relationships that describe the macroscale frictional behavior of a broad range of materials, including rocks found in the seismogenic zone of Earth's crust. A fundamental aspect of the RSF laws is frictional ``aging,'' where friction increases with the time of stationary contact due to asperity creep and/or interfacial strengthening. Recent atomic force microscope (AFM) experiments and simulations found that nanoscale silica contacts exhibit aging due to the progressive formation of interfacial Chemical Bonds. The role of normal load (and, thus, normal stress) on this interfacial Chemical Bond-induced (ICBI) friction is predicted to be significant but has not been examined experimentally. Here, we show using AFM that, for nanoscale ICBI friction of silica-silica interfaces, aging (the difference between the maximum static friction and the kinetic friction) increases approximately linearly with the product of the normal load and the log of the hold time. This behavior is attributed to the approximately linear dependence of the contact area on the load in the positive load regime before significant wear occurs, as inferred from sliding friction measurements. This implies that the average pressure, and thus the average Bond formation rate, is load independent within the accessible load range. We also consider a more accurate nonlinear model for the contact area, from which we extract the activation volume and the average stress-free energy barrier to the aging process. Our work provides an approach for studying the load and time dependence of contact aging at the nanoscale and further establishes RSF laws for nanoscale asperity contacts.
Wenqing Zhang - One of the best experts on this subject based on the ideXlab platform.
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thermal transport in thermoelectric materials with Chemical Bond hierarchy
Journal of Physics: Condensed Matter, 2019Co-Authors: Jiong Yang, Yancheng Wang, Hongliang Yang, Wei Tang, Jihui Yang, Lidong Chen, Wenqing ZhangAbstract:Chemical Bond hierarchy (CBH) depicts a unique structural type of solids, in which fractions of the materials are loosely Bonded in a relatively rigid framework. The weak Bonding in materials with CBH induces special atomic vibrational motions and has a significant influence on the thermoelectric transport properties. The architecture of compounds with CBH was first proposed by Slack in his 'phonon glass electron crystal' paradigm and has led to the discovery of numerous new thermoelectric compounds over the years. This review covers various types of thermoelectric materials with different levels of CBH, focusing on their lattice thermal conductivities (κ Ls). Caged compounds, with foreign impurities in the cages as the rattlers, are the first type of compounds stimulating the study of CBH. The fillers in both the clathrates and the filled skutterudites greatly reduce the κ L accompanied by abnormal temperature dependence. As reviewed herein, the reduced κ L is attributed to different mechanistic sources, i.e., the resonant scattering or the enhanced anharmonic phonon scatterings. Both may contribute to the κ L reductions. In recent years, more materials with different types of CBH have been discovered, some containing complex atomic clusters as the rattlers, and others having flowing atoms that cause multiple equilibrium sites and even liquid-like behaviors. All CBHs strongly interfere with the heat transport of the corresponding materials. Future perspectives and possible research directions for thermal transport in thermoelectric materials with CBH have also been summarized herein.
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high thermoelectric performance in te free bi sb 2se3via structural transition induced band convergence and Chemical Bond softening
Energy and Environmental Science, 2016Co-Authors: Shanyu Wang, Jiong Yang, Wenqing Zhang, Yongxing Sun, Bo Duan, Jihui YangAbstract:Semiconductors with converging multiple electronic valleys and soft Chemical Bonds are ideal for high-performance thermoelectrics. Narrow gap Bi2Se3 is a well-known three-dimensional topological insulator with non-trivial surface states, while possessing low thermoelectric properties due to its single-degenerate band conduction, despite being an important constituent of highly efficient n-type thermoelectric Bi2(Te,Se)3. Here we demonstrate that in Te-free Bi2−xSbxSe3 converging multiple electronic band valleys and strengthening phonon scattering can be realized simultaneously via a composition-induced (Sb-alloying) structural transition from a rhombohedral phase to an orthorhombic phase. The accompanying Chemical Bond softening and structural distortion cause significant modifications to the electronic band structure and phonon dispersion. The convergence of heavy bands realized in the orthorhombic phase (x ≥ 1.0) largely increases the electron density of states effective mass, and thus gives rise to a high Seebeck coefficient of ∼−280 μV K−1 at 800 K. Meanwhile, phonon softening and substantial lattice anharmonicity pertain to weak interchain interactions considerably block the heat-carrying acoustic phonons, resulting in ultralow lattice thermal conductivities of ∼0.6 W m−1 K−1 at 300 K and ∼0.3 W m−1 K−1 at 800 K. Consequently, a maximum thermoelectric figure of merit ZT of ∼1.0 can be achieved for n-type BiSbSe3, about three times higher than that of the optimized Bi2Se3. The moderately high ZT of Te-free BiSbSe3 makes it a promising candidate for low-mid temperature power generations. Furthermore, the concept of structural transition driven band convergence and Chemical Bond softening can be applied to improve the thermoelectric properties of other materials and may also shed light on identifying new materials.
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part crystalline part liquid state and rattling like thermal damping in materials with Chemical Bond hierarchy
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Wujie Qiu, Jihui Yang, Wenqing Zhang, Ping WeiAbstract:Understanding thermal and phonon transport in solids has been of great importance in many disciplines such as thermoelectric materials, which usually requires an extremely low lattice thermal conductivity (LTC). By analyzing the finite-temperature structural and vibrational characteristics of typical thermoelectric compounds such as filled skutterudites and Cu3SbSe3, we demonstrate a concept of part-crystalline part-liquid state in the compounds with Chemical-Bond hierarchy, in which certain constituent species weakly Bond to other part of the crystal. Such a material could intrinsically manifest the coexistence of rigid crystalline sublattices and other fluctuating noncrystalline sublattices with thermally induced large-amplitude vibrations and even flow of the group of species atoms, leading to atomic-level heterogeneity, mixed part-crystalline part-liquid structure, and thus rattling-like thermal damping due to the collective soft-mode vibrations similar to the Boson peak in amorphous materials. The observed abnormal LTC close to the amorphous limit in these materials can only be described by an effective approach that approximately treats the rattling-like damping as a “resonant” phonon scattering.
Siyuan Zhang - One of the best experts on this subject based on the ideXlab platform.
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Chemical Bond characteristics thermal expansion property and compressibility of ar2o4 a ca sr ba r rare earths
Materials Chemistry and Physics, 2009Co-Authors: Siyuan Zhang, Shihong Zhou, Xueqiang CaoAbstract:Abstract Theoretical researches were performed on the CaFe 2 O 4 -type binary rare earth oxides AR 2 O 4 (A = Ca, Sr, Ba; R = rare earths) by using Chemical Bond theory of dielectric description. The Chemical Bond properties of these crystals were explored, and then the thermal expansion property and compressibility were studied. The theoretical values of linear thermal expansion coefficient (LTEC) and bulk modulus were presented. The calculations revealed that the LTECs and the bulk moduli do have linear relationship with the ionic radii of the rare earths. In the cases of Sc and Y, both the LTEC and bulk modulus values are larger than the lanthanide series. We attribute this to the difference in the electronic configuration between Sc (Y) and lanthanide series. For SrY 2 O 4 and BaY 2 O 4 crystals, the theoretical values of LTEC and bulk modulus agree well with experimental ones.
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calculation of bulk modulus on carbon nitrides with Chemical Bond method
Applied Physics Letters, 2007Co-Authors: Siyuan Zhang, Huaiyong Li, Ling Li, Shihong ZhouAbstract:The bulk moduli of some superhard materials were calculated by using the Chemical Bond method. For simple crystals, such as diamonds, c-BN, SiC, Si, BP, and Ge, the calculated results agree with experimental and theoretical values. For crystals of complex structure, such as β-BC2N crystal and various structural C3N4 crystals, the results indicate that their bulk moduli are large, but do not exceed that of diamond.
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calculation of the bulk modulus of simple and complex crystals with the Chemical Bond method
Journal of Physical Chemistry B, 2007Co-Authors: Siyuan Zhang, Huiling Li, H Z Li, Shihong ZhouAbstract:The relation between the lattice energies and the bulk moduli on binary inorganic crystals was studied, and the concept of lattice energy density is introduced. We find that the lattice energy densities are in good linear relation with the bulk moduli in the same type of crystals, the slopes of fitting lines for various types of crystals are related to the valence and coordination number of cations of crystals, and the empirical expression of calculated slope is obtained. From crystal structure, the calculated results are in very good agreement with the experimental values. At the same time, by means of the dielectric theory of the Chemical Bond and the calculating method of the lattice energy of complex crystals, the estimative method of the bulk modulus of complex crystals was established reasonably, and the calculated results are in very good agreement with the experimental values.
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dependence of charge transfer energy on crystal structure and composition in eu3 doped compounds
Journal of Physical Chemistry B, 2006Co-Authors: Ling Li, Siyuan ZhangAbstract:We report a method for estimating the positions of charge transfer (CT) bands in Eu3+-doped complex crystals. The environmental factor (he) influencing the CT energy is presented. he consists of four Chemical Bond parameters: the covalency, the Bond volume polarization, the presented charge of the ligand in the Chemical Bond, and the coordination number of the central ion. These parameters are calculated with the dielectric theory of complex crystals. The relationship between the experimental CT energies and calculated environmental factors was established by an empirical formula. The calculated values are in good agreement with the experimental results. Such a relationship was confirmed by detailed analysis. In addition, our method is also useful to predict the charge-transfer position of any other rare earth ion.
Shuren Zhang - One of the best experts on this subject based on the ideXlab platform.
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characterization of structure Chemical Bond and microwave dielectric properties in ca0 61nd0 26tio3 ceramic substituted by chromium for titanium
Journal of Alloys and Compounds, 2020Co-Authors: Zhe Xiong, Bin Tang, Fuchuan Luo, Hongyu Yang, Xing Zhang, Chengtao Yang, Zixuan Fang, Shuren ZhangAbstract:Abstract We studied the phase constitutions, microstructure, Chemical Bond and microwave dielectric properties for Ca0.61Nd0.26Ti1-xCrxO3 (0 ≤ x ≤ 0.03) ceramics synthesized by solid-state reaction using SEM, X-ray diffractometer, Raman spectroscopy, microwave measuring system, etc. Although the second phase TiO2 appeared when x ≥ 0.015 as presented in XRD patterns, TiO2 was confirmed to have no effects on the tendency of microwave dielectric properties as a function of x value. The SEM images showed that the grain size decreased as Cr content increased, which could be explained by that doping Cr increased the grain boundary energy or decreased surface energy for Ca0.61Nd0.26TiO3 ceramic. The SRO effects enhanced with increase of Cr substitution, which was verified by Raman spectra. The dielectric constant and τf value were concerned with the average ionicity of Chemical Bond and the ionic polarizability for Ca0.61Nd0.26Ti1-xCrxO3 ceramics. The SEM images suggested that the optimized sintering temperatures was 1400 °C for samples with x = 0.01. The XPS spectra and the trend of Q × f value indicated that the balanced amount of Cr substitution could restrain the generation of Ti3+. Hence, the Q × f value of Ca0.61Nd0.26Ti1-xCrxO3 ceramics reached the maximum of 16,078 GHz at x = 0.01 compared with that of 11,425 GHz in pure Ca0.61Nd0.26TiO3 ceramic.
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structural dependence of microwave dielectric properties of spinel structured mg2 ti1 xsnx o4 solid solutions crystal structure refinement raman spectra study and complex Chemical Bond theory
Ceramics International, 2019Co-Authors: Pengcheng Zhang, Bin Tang, Hongyu Yang, Shuren ZhangAbstract:Abstract Mg2(Ti1-xSnx)O4 (x = 0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex Chemical Bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average Bond covalency. The relationship among the B-site octahedral Bond energy, tetrahedral Bond energy and temperature coefficient are discussed by defining on the change rate of Bond energy and the contribution rate of octahedral Bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained ( e r = 12.18, Q × f = 170,130 GHz, τ f = −53.1 ppm/°C, x = 0.2).