Bulk Thermal Expansion Coefficient Research Articles

Measuring nanoscale thermal gradients in suspended MoS2 with STEM-EELS

Transition metal dichalcogenides such as molybdenum disulfide (MoS2) may see service in the heart of next-generation nanoelectronic devices, where highly localized power dissipation can produce nontrivial temperature gradients over nanometer-scale distances. Here, we demonstrate that MoS2 is a promising target for plasmon energy expansion thermometry (PEET), a high-spatial resolution temperature mapping technique employed in a scanning transmission electron microscope (STEM) equipped with electron energy loss spectroscopy (EELS). We first use a calibrated, commercial MEMS-style TEM sample heater chip to measure the temperature dependence of the MoS2 bulk plasmon. We corroborate the chip's temperature calibration with Raman thermometry and determine the bulk thermal expansion coefficient (TEC) of MoS2 in the temperature range of 300–1100 K. Applying this TEC value to PEET measurements on a suspended MoS2 flake, we map 70–90 K/μm temperature gradients with a submicrometer spatial resolution.

Impact of La2O3/Y2O3 ratio on crystallization kinetics of CaO based alumino-borosilicate glasses and compatibility with Crofer and 8YSZ for SOFCs

In the present investigation, the novel glass series xLa2O3-(10-x)Y2O3-15SrO-15CaO-10B2O3-10Al2O3-40SiO2 (x = 2, 4, 6, 8) has been synthesized by melt quenching technique. The characteristic glass temperatures and the inflection point temperature (Tf) for the glasses have been determined by DTA and differential DTA (DDTA), respectively. The activation energy is calculated using Kissinger, Moynihan and Augis and Benett models. Various kinetic parameters such as fluctuation free volume (fg), Hruby parameter (Hr), bulk thermal expansion coefficient (αf) and k parameters are calculated for studying glass stability with varying La2O3/Y2O3 ratio. The amorphous nature and crystalline phase formation has been studied by X-ray diffraction. Furthermore, the coefficient of thermal expansion (CTE) for all the glasses has been calculated. The interaction studies of the diffusion couples of glasses with pre-oxidized Crofer 22APU and 8YSZ have been carried out at 850 °C. 2 LaY glass is very stable and promising potential sealant for the SOFCs.

Effect of temperature and pressure on electronic and spectroscopic properties of CdS wurtzoid molecule: A DFT study

Temperature and pressure effects on cadmium Sulfide wurtzoid molecule Cd7S7 are investigated using density functional theory. This molecule is of 0.77 nm length. The investigated molecule represents the smallest cluster of atoms from wurtzoids molecules series that shows a hexagonal structure and represents the bulk wurtzite phase as the cluster increases in size. The investigation includes the effect of pressure and temperature on electronic and vibrational properties. The volume change of this molecule is controlled by the bulk modulus and thermal expansion coefficient. Theoretical and experimental results show that both bulk modulus and thermal expansion are more than three times their values at bulk. The results show that increasing the pressure increases the energy gap and Raman longitudinal optical mode due to contraction of the molecule. On the other hand, temperature decreases the energy gap and Raman longitudinal optical mode due to dilation of the molecule. Present results are in good agreement with available experimental results. The electronic orbitals and charges are affected due to pressure and temperature. At high pressure, some electronic charge transforms from S atoms to Cd atoms. At high temperature, the reverse electronic emigration occurs. Orbital occupations change inside each atom itself due to pressure and temperature.

Thermal expansion, compressibility and bulk modulus of ilmenite-type CoTiO3: X-ray diffraction at high pressures and temperatures

In this paper we report about the in-situ experiments on cobalt titanate (CoTiO3), in which were investigated the compressibility at high pressures up to 24.6 GPa, at room temperature, using synchrotron X-ray diffraction (SXRD) and also the thermal expansion at high temperatures, from 298 to 723 K, using a conventional diffractometer at atmospheric pressure. The diffraction patterns were analyzed using the Rietveld method. The obtained lattice parameters were used to determine thermodynamic data of the CoTiO3 in its ilmenite phase: the bulk modulus, compressibility, and thermal expansion coefficients. It was observed that increasing pressure, the volume of the unit cell decreased from 306.16 Å3 to 266.01 Å3. The third-order Birch-Murnaghan equation of state was fitted to determine the bulk modulus, B0, and its pressure derivative, B0' along with the compressibility of the a- and c-crystallographic axis. In contrast, increasing temperature caused a volumetric expansion of the unit cell from 306.16 Å3 to 309.92 Å3. In both cases, changes in the c-axis dominate the expansion or contraction of the unit cell. Within the pressure and temperature ranges investigated in this paper, no structural phase transition was observed.

Pressure, temperature, and heat flux in high speed lubrication flows of pressurized gases

Abstract We present approximate solutions to the compressible Reynolds equation and the corresponding temperature equation which are valid for large speed numbers in the dense and supercritical gas regime. The flows are taken to be two-dimensional, steady, compressible, single-phase and laminar. New results include explicit formulas for pressure, density, temperature, and heat flux in terms of the speed number, film thickness function, and the material functions. We have found that the first correction for finite speed number will depend on the local values of the effective bulk modulus and thermal expansion coefficient. Our approximations are compared to numerical solutions to the exact Reynolds theory. It was found that the first order approximation is necessary to obtain realistic pressure and temperature distributions.

Zr0.70[Y1-xNdx]0.30O1.85 as a potential candidate for inert matrix fuel: Structural and thermo-physical property investigations

In order to mimic the loading of americium (Am) and curium (Cm) oxide in yttria stabilized zirconia, Zr0.70 [Y1-xNdx]0.30O1.85 (0.0 ≤ x ≤ 1.0) system was synthesized by solid state route and characterized by X-ray diffraction (XRD) and Raman spectroscopy. The entire system appeared single-phasic fluorite-type by XRD. However, Raman spectroscopy revealed the existence of tetragonal domains for the Nd-rich composition, Zr0.70Nd0.30O1.85 (x = 1.0). Bulk thermal expansion coefficient was found to increase with increasing NdO1.5 content in this series in the temperature range 298–1473 K. The heat capacity of sintered samples was measured by heat flux-type differential scanning calorimeter over the temperature range 313–713 K and it was observed to decrease with increasing Nd3+-content. Thermal conductivity values were determined from measured thermal diffusivity, temperature dependent density and specific heat capacity values. The thermal conductivity of Nd3+ stabilized zirconia was lower than yttria stabilized zirconia.

Theoretical Study of Structural, Magnetic, Elastic, Phonon, and Thermodynamic Properties of Heusler Alloys Fe2CrX (X = Al, Ga)

First-principle calculations based on generalized gradient approximation and quasi-harmonic Debye model were executed to analyze the structural, magnetic, elastic, phonon, and thermodynamic properties of Fe2CrX (X = Al, Ga) Heusler alloys. The computed lattice parameters concurred well with available experimental and theoretical data. The calculated elastic constants reveal that the Fe2CrAl is brittle and Fe2CrGa is ductile. The phonon dispersion relation of Fe2CrX (X = Al, Ga) are calculated using finite displacement method with a cutoff radius of 5 A. We likewise explored the thermodynamic properties by utilizing quasi-harmonic Debye model in which bulk modulus, heat capacity, Debye temperature, Gruneisen parameter, and thermal expansion coefficient are resolved at 0–30 Gpa pressure and 0–900 K temperature from the non-equilibrium Gibbs functions.

Influence of CaO/MgO ratio on the crystallization kinetics and interfacial compatibility with crofer 22APU and YSZ of strontium based alumino-borosilicate glasses for SOFC applications

High temperature hermetic sealants are required for the stability and good efficiency of the solid oxide fuel cells (SOFCs). Glass and glass ceramics are promising sealant materials due to their desirable properties and flexible compositions. In the present study, the novel glass series (10 + x) CaO-(10 − x) MgO-10SrO-10B2O3-20Al2O3-40SiO2 (x = 0, 2.5, 5, 7.5) has been synthesized via melt quenching route. These glass/glass ceramics are characterized by X-ray diffraction to evaluate the amorphous nature and phase formation, respectively. The activation energy has been analyzed by using three different theoretical models – Kissinger Model, Moynihan Model and Augis and Benett Model. In addition to this, the characteristic glass temperatures and coefficient of thermal expansion (CTE) have been obtained from DTA, differential DTA (DDTA) and Dilatometry. Various stability parameters like Hruby parameter, Saad Parameter, fluctuation free volume (fg) and bulk thermal expansion coefficient (αf) are also calculated with varying CaO/MgO ratio (R). Furthermore, to analyze the stability of the glasses with varying CaO/MgO ratio over a broader range of temperature, k parameters i.e. kb (T) and kf (T) are also evaluated for different heating rates. The diffusion couples of glasses with pre oxidized Crofer 22APU and YSZ fabricated at 850 °C for 500 h have been characterized using scanning electron microscopy (SEM) and X-ray dot mapping to investigate the sealing characteristics with varying CaO/MgO ratio. The glass series 15 CaMg is very stable and promises to be a good sealant for solid oxide fuel cells.

Analysis of the thermoelastic properties of nanocrystalline Foresterite using a thermodynamic equation of state

A new potential independent equation of state is used in the present work to analyze the thermo-elastic properties of nanocrystalline Foresterite (nc- Fo) under varying temperature and pressure conditions. The newly developed EOS is found to be valid for explaining the elastic behavior of nanocrystalline forsterite satisfactorily over the temperature range from 300K to 1573K with a pressure variation from 0 to 9.6GPa. The values calculated for the volume compression under varying temperature- pressure conditions are compared with the available experimental data and also with those obtained by using different approaches. It is found that the results obtained in the present study are more close to the experimental data in comparison to those reported earlier. The same model is further extended to study the variation in the bulk modulus and thermal expansion coefficient of Foresterite nano-mineral ver the temperature range from 300K to 1573K. The results show the same trend of expansion as observed in single nanocrystals at high temperature.

Comparative study of Mo2Ga2C with superconducting MAX phase Mo2GaC: First-principles calculations

The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states (DOS) is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters (e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function) are calculated for the first time. The study of dielectric constant (ɛ1) indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values (DOS, Debye temperature, atomic mass, etc.) suggests that the compound is less likely to be superconductor.

Elastic, thermodynamic and optical behavior of V2AC (A = Al, Ga) MAX phases

This article reports the first-principles calculations of yet unexplored Mulliken bond population, Vickers hardness, thermodynamic and optical properties of MAX phases V2AC (A=Al, Ga). We have also revisited the structural and elastic properties of these phases in order to assess the reliability of our calculations. The temperature and pressure dependence of bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient have been successfully estimated through the quasi-harmonic Debye model in the temperature range from 0 to 1000K and the pressure range from 0 to 50GPa. The optical properties such as the dielectric function, refractive index, photoconductivity, absorption coefficients, reflectivity and loss function are also evaluated for the first time. The reflectivity is found to be high which indicates that V2AC (A=Al, Ga) having the same characteristics could be good candidate materials to reduce solar heating up to ∼15eV.

Structural, mechanical and thermodynamic properties of Ti2AlX (X= C, N) at high pressure

The MAX phase has attracted much attention due to its unique properties combined with the merits of both metal and ceramic, including the low density, high electrical conductivity and good oxidation resistance, which makes it significant for possible applications in various high temperature or other environments. There is a lot of research work on Ti2AlX (X=C, N). However little research about thermodynamic properties at high pressure is carried out. So we study the structural, mechanical and thermodynamic properties of Ti2AlC and Ti2AlN at various pressures and temperatures. The first-principles calculations based on electronic density-functional theory framework are used to investigate the properties at various pressures. The cut-off energy is 350 eV. Converged results are achieved with 10102 special K-point meshes. The self-consistent convergence of total energy is set to be 5.010-6 eV/atom. According to the calculated structural parameters at various pressures, we can find that the ratios V/V0 (V0 denotes the system volume at 0 GPa) of Ti2AlX are reduced by 20.59% and 18.93%, respectively, so the compressibility of the system is strong. As the internal pressure increases, the curves of V/V0 become gentle. Then we calculate elastic constants at pressures ranging from 0 to 50 GPa in steps of 10 GPa. It is obvious that the Ti2AlX is mechanically stable because all of the elastic constants satisfy the Born stability criteria. The bulk modulus, shear modulus and Young's modulus linearly increase with internal pressure increasing, implying that the pressure can improve the resistance to volume deformation. The ductility and brittleness can be judged according to Pugh's criterion (ratio of bulk modulus to shear modulus B/G), and the brittle nature turns into ductile nature in a pressure range of 40-50 GPa for the Ti2AlX since the value of B/G exceeds 1.75. Finally, we study the thermodynamic properties at various pressures and temperatures based on the quasi-harmonic Debye approximation theory, including the bulk modulus, heat capacity and thermal expansion coefficient. The bulk modulus decreases with temperature increasing but increases with pressure increasing. The heat capacity at constant volume Cv and the heat capacity at constant pressure Cp have the same variation tendency, while Cv obeys the Dulong-Petit limit. It is easy to see that temperature and pressure have opposite influences on heat capacity and the effect of temperature is more significant than that of pressure. The effects of temperature and pressure on linear expansion coefficient mainly occur at low temperature and the effect of pressure is not so considerable when the pressure exceeds 30 GPa. Above all, the effects of temperature and pressure on thermodynamic properties are inverse.

Structural evolution and strength change of a metallic glass at different temperatures.

The structural evolution of a Zr64.13Cu15.75Ni10.12Al10 metallic glass is investigated in-situ by high-energy synchrotron X-ray radiation upon heating up to crystallization. The structural rearrangements on the atomic scale during the heating process are analysed as a function of temperature, focusing on shift of the peaks of the structure factor in reciprocal space and the pair distribution function and radial distribution function in real space which are correlated with atomic rearrangements and progressing nanocrystallization. Thermal expansion and contraction of the coordination shells is measured and correlated with the bulk coefficient of thermal expansion. The characteristics of the microstructure and the yield strength of the metallic glass at high temperature are discussed aiming to elucidate the correlation between the atomic arrangement and the mechanical properties.

Design of Nonperiodic Microarchitectured Materials That Achieve Graded Thermal Expansions

The aim of this paper is to introduce an approach for optimally organizing a variety of nonrepeating compliant-mechanism-like unit cells within a large deformable lattice such that the bulk behavior of the lattice exhibits a desired graded change in thermal expansion while achieving a desired uniform stiffness over its geometry. Such lattices with nonrepeating unit cells, called nonperiodic microarchitectured materials, could be sandwiched between two materials with different thermal expansion coefficients to accommodate their different expansions and/or contractions induced by changing ambient temperatures. This capability would reduce system-level failures within robots, mechanisms, electronic modules, or other layered coatings or structures made of different materials with mismatched thermal expansion coefficients. The closed-form analytical equations are provided, which are necessary to rapidly calculate the bulk thermal expansion coefficient and Young's modulus of general multimaterial lattices that consist first of repeating unit cells of the same design (i.e., periodic microarchitectured materials). Then, these equations are utilized in an iterative way to generate different rows of repeating unit cells of the same design that are layered together to achieve nonperiodic microarchitectured material lattices such that their top and bottom rows achieve the same desired thermal expansion coefficients as the two materials between which the lattice is sandwiched. A matlab tool is used to generate images of the undeformed and deformed lattices to verify their behavior and an example is provided as a case study. The theory provided is also verified and validated using finite-element analysis (FEA) and experimentation.

The Effect of Alumina (Al<sub>2</sub>O<sub>3</sub>) on the Characteristics of Sintered Mullite-Cordierite Ceramics Synthesized with Kaolin from Naratiwas of Thailand

Mullite-cordierite ceramics was prepared by the three composition of talc, kaolin (kaolin from Naratiwas in Thailand) (NT) and alumina. The different amounts of alumina (5, 10, 15 and 20 wt%) were added to produce various mullite-cordierite alumina mixtures which are denoted as NA, NB, NC and ND, respectively. The mixtures were pressed into rectangular shapes by hydraulic press with the pressure of 150 kg/cm2 then sintered at temperature of 1300 °C and 1350 °C for 2 hours. The morphology of the synthesized mullite-cordierite samples were characterized by x-ray diffraction spectroscopy (XRD), and physical-mechanical properties were investigated. Mullite-cordierite was successfully synthesized. The XRD result was represented phases of mullite and cordierite. The NA samples sintered at temperature of 1300 °C indicated the best physical-mechanical properties including bulk density (2.23 g/cm3), flexural strength (44.4 MPa) and thermal expansion coefficients (5.00x10-6). The other NA samples sintered at temperature of 1350 °C exhibited the bulk density, flexural strength and thermal expansion coefficients are 2.21 g/cm3, 47.8 MPa and 4.99 x10-6, respectively. The thermal expansion coefficient of the NT sintered samples have been plotted the length change relative to measuring temperature ranging of 30-1200 °C. The suitable condition of the synthesized mullite-cordierite ceramics is finally obtained the NA samples with 5 percent weight of alumina composition sintered at the temperature of 1350 °C.

Unravelling the low thermal expansion coefficient of cation-substituted YBaCo4O7+δ

With an aim to understand the origin of the low thermal expansion coefficients (TECs), cation-substituted YBaCo4O7-type oxides have been investigated by in-situ neutron diffraction, bond valence sum (BVS), thermogravimetric analysis, and dilatometry. The compositions YBaCo3ZnO7+δ, Y0.9In0.1BaCo3ZnO7+δ, and Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ were synthesized by solid-state reaction at 1200 °C. Rietveld refinement of the joint synchrotron X-ray and neutron diffraction data shows that the Zn and Fe dopants have different preferences to substitute the Co ions in the 6c and 2a sites. The bulk thermal-expansion coefficients of YBaCo3ZnO7+δ, Y0.9In0.1BaCo3ZnO7+δ, and Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ are, respectively, 9.42, 9.76, and 9.06 × 10−6 °C−1. Neutron diffraction data show that the low anisotropic TEC along the a-axis is the main contributor to the low bulk TECs. With the substitution of In, Zn, and Fe in Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ, the anisotropic and bulk TECs could be reduced to 8.94 and 9.06 × 10−6 °C−1, respectively, mainly due to the suppression of the change in Co–O bond length in CoO4 polyhedra. The observed weight loss during heating is due to the loss of interstitial oxide ions, as revealed by neutron diffraction and BVS map. Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ has the lowest area-specific cathodic polarization resistance of 0.14 Ω cm2 (Rtotal/2) at 700 °C in air.

Electronic, optical and thermal properties of TiCr2 and TiMn2 by ab initio simulations

A theoretical study of TiX2 (X = Cr, Mn) with C14 Laves phase compounds has been performed by using the first-principles pseudopotential plane-wave method within the generalized gradient approximation (GGA). The electronic properties (Fermi surface and charge density) have been calculated and analyzed. The optical characteristics (dielectric functions, absorption spectrum, conductivity, energy-loss spectrum and reflectivity) are calculated and discussed. The calculated large positive static dielectric constant indicates good dielectric properties. The reflectivity of TiX2 (X = Cr, Mn) is high in the IR–Visible–UV region up to [Formula: see text][Formula: see text]13 eV showing promise as a good solar heating barrier material. The temperature and pressure dependence of bulk modulus, Debye temperature, specific heats and thermal expansion coefficient are obtained for T = 1200 K and P = 50 GPa through quasi-harmonic Debye model with phononic effects. Fermi surface, optical and thermodynamic properties are very important for practical applications of the materials in optical and other devices.

Phase transition and thermodynamic properties of beryllium telluride under high pressure

A theoretical investigation on structural, dynamical, phase diagram and thermodynamic properties of beryllium telluride (BeTe) under high pressure and temperature is presented in the framework of density functional theory. The calculated structural parameters of BeTe in both zinc blende (ZB) and nickel arsenide (NiAs) structures are in reasonable agreement with available experimental data and previous theoretical work. The phonon dispersion relations, dielectric tensor and Born effective charge are investigated within the density functional perturbation theory (DFPT). The investigation of the phase diagram indicated that the NiAs structure BeTe becomes stable at high pressure and temperature. Based on the quasiharmonic Debye model, the pressure and temperature dependences of bulk modulus, Grüneisen parameter, Debye temperature, specific heat and thermal expansion coefficient are all successfully obtained. We hope that the theoretical results reported here can give more insight into the structural and thermodynamic properties of other semiconductors at high temperature and pressure.

Physical properties of tetragonal transition-metal borides Nb2MB2 (M = Mo, W, Re or Os) with a new superstructure

The mechanical and thermodynamic properties, chemical bonding characteristics and electronic structure of Nb2MB2 (M = Mo, W, Re or Os) with a new tetragonal U3Si2-type superstructure (space group P4/mnc, no. 128) were studied by means of density functional theory calculations. All Nb2MB2 structures studied were demonstrated to be thermodynamically and mechanically stable. The bulk, shear and Young's moduli, Poisson's ratio, Debye temperature and anisotropy factors were derived for ideal polycrystalline Nb2MB2 aggregates. Among these compounds, Nb2WB2 was found to have the highest shear modulus and hardness. The electronic densities of state and electronic localization function analysis revealed the metallicity and strong covalent B–B, Nb–B and M−B bonding in Nb2MB2. Moreover, these results reveal that the covalence between Nb 4d, M nd (n = 4 for Mo and 5 for W, Re and Os) and B 2p states is the cause of the relatively higher elastic modulus and hardness of the Nb-based compounds. Finally, thermodynamic properties, including the bulk modulus, heat capacity and thermal expansion coefficient of Nb2WB2 were obtained systematically under high temperature and pressure.

Thermal and kinetic parameters of 30Li2O–55B2O3–5ZnO–xTiO2–(10−x)V2O5 (0 ≤ x ≤ 10) glasses

In the present investigation, the effects of titanium and vanadium concentration on the thermal properties have been studied for 30Li2O–55B2O3–5ZnO–xTiO2–(10−x)V2O5 (0 ≤ x ≤ 10) glasses. To understand the crystallization mechanics, activation energy has been calculated using two different approaches, i.e., Kissinger model and Augis and Bennett model. Using the derivative differential thermal analysis, the inflection point temperature (Tf) and crystallization constants ky(T) and kf(T), for different heating rates, have also been obtained for all the glasses. Furthermore, kinetic parameters such as fluctuation free volume (fg) and change in bulk thermal expansion coefficient (αf) have been calculated for all the glass samples. The replacement of V2O5 by TiO2 induces phase separation in glasses.