scholarly journals Effects of Al substitution by Si in Ti3AlC2 nanolaminate

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. A. Hadi ◽  
Md Roknuzzaman ◽  
M. T. Nasir ◽  
U. Monira ◽  
S. H. Naqib ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Solid Solutions ◽  
Density Functional ◽  
Visible Region ◽  
Coating Materials ◽  
Cell Parameters ◽  
Barrier Coating ◽  
Cauchy Pressure ◽  
Potential Applications ◽  
Temperature Lattice

AbstractRecently, a series of high-purity Ti3(Al1−xSix)C2 solid solutions with new compositions (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been reported with interesting mechanical properties. Here, we have employed density functional theory for Ti3(Al1−xSix)C2 solid solutions to calculate a wider range of physical properties including structural, electronic, mechanical, thermal and optical. With the increase of x, a decrease of cell parameters is observed. All elastic constants and moduli increase with x. The Fermi level gradually increases, moving towards and past the upper bound of the pseudogap, when the value of x goes from zero to unity, indicating that the structural stability reduces gradually when the amount of Si increases within the Ti3(Al1−xSix)C2 system. In view of Cauchy pressure, Pugh’s ratio and Poisson’s ratio all compositions of Ti3(Al1−xSix)C2 are brittle in nature. Comparatively, low Debye temperature, lattice thermal conductivity and minimum thermal conductivity of Ti3AlC2 favor it to be a thermal barrier coating material. High melting temperatures implies that the solid solutions Ti3(Al1−xSix)C2 may have potential applications in harsh environments. In the visible region (1.8–3.1 eV), the minimum reflectivity of all compositions for both polarizations is above 45%, which makes them potential coating materials for solar heating reduction.

Physical properties of ThCr2Si2-type Rh-based compounds ARh2Ge2(A = Ca, Sr, Y and Ba): DFT based first-principles investigation

2018 ◽  
Vol 32 (32) ◽  
pp. 1850357 ◽  
Author(s):  
M. U. Salma ◽  
Md. Atikur Rahman
Keyword(s):  
Thermal Conductivity ◽  
Density Of States ◽  
Density Functional ◽  
Partial Density ◽  
Total Density ◽  
Coating Materials ◽  
Metallic Behavior ◽  
Density Maps ◽  
Debye Temperatures ◽  
Low Energies

In this paper, we have explored the physical, mechanical, chemical bonding, dialectical and thermodynamic properties of ARh2Ge2 (A = Ca, Sr, Y and Ba) theoretically for the first time. This investigation has been completed by density functional theory (DFT) calculations with the help of CASTEP code. The structural optimized factors of ARh2Ge2 (A = Ca, Sr, Y and Ba) are in excellent concurrence with the existing experimental data. The observed elastic constants are positive and prove the mechanical constancy for all these compounds. The calculated Pugh’s ratio and Poisson’s ratio show the ductile behaviors of Ca/YRh2Ge2 and brittleness behaviors of Sr/BaRh2Ge2, whereas the Cauchy pressure indicates the ductility for all these phases. The anisotropic factors, universal anisotropy indicator and fraction of anisotropy in compression and shear ensure the elastically anisotropic nature for all these phases. Bulk modulus and hardness values indicate that Sr/BaRh2Ge2 are soft and easily machinable in comparison with Y/CaRh2Ge2. The analysis of the band structure diagrams as well as density of states (total density of states and partial density of states) evidence the metallic behavior for all the compounds. The analysis of Mulliken bond populations and charge density maps give the existence of covalent and metallic bonding in these compounds. The optical properties point out that all phases can be used as coating materials at low energies. For all the phases the Debye temperatures have been calculated via elastic constant data. We have also evaluated the minimum thermal conductivity for these compounds. All compounds possess the relatively low minimum thermal conductivity with the low value of Debye temperatures which also evidence that all compounds could be applied like thermal fence covering material.

scholarly journals Thermoelectric Properties of Hexagonal M2C3 (M = As, Sb, and Bi) Monolayers from First-Principles Calculations

Nanomaterials ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 597 ◽  
Author(s):  
Xue-Liang Zhu ◽  
Peng-Fei Liu ◽  
Guofeng Xie ◽  
Wu-Xing Zhou ◽  
Bao-Tian Wang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Density Functional ◽  
Optical Absorption Coefficient ◽  
Boltzmann Transport ◽  
Low Thermal Conductivity ◽  
Phonon Group Velocity ◽  
Optical Modes ◽  
Potential Applications ◽  
High Seebeck Coefficient ◽  
Phonon Relaxation Time

Hexagonal M2C3 compound is a new predicted functional material with desirable band gaps, a large optical absorption coefficient, and ultrahigh carrier mobility, implying its potential applications in photoelectricity and thermoelectric (TE) devices. Based on density-functional theory and Boltzmann transport equation, we systematically research the TE properties of M2C3. Results indicate that the Bi2C3 possesses low phonon group velocity (~2.07 km/s), low optical modes (~2.12 THz), large Grüneisen parameters (~4.46), and short phonon relaxation time. Based on these intrinsic properties, heat transport ability will be immensely restrained and therefore lead to a low thermal conductivity (~4.31 W/mK) for the Bi2C3 at 300 K. A twofold degeneracy is observed at conduction bands along Γ-M direction, which gives a high n-type electrical conductivity. Its low thermal conductivity and high Seebeck coefficient lead to an excellent TE response. The maximum thermoelectric figure of merit (ZT) of n-type can approach 1.41 for Bi2C3. This work shows a perspective for applications of TE and stimulate further experimental synthesis.

scholarly journals Optimization of the thermophysical properties of the thermal barrier coating materials based on GA-SVR machine learning method: illustrated with ZrO2 doped DyTaO4 system

2021 ◽  
Author(s):  
Zhu Wen Jie ◽  
Mengdi Gan ◽  
Bo Ye ◽  
Xin Xiong ◽  
Feng Jing ◽  
...  
Keyword(s):  
Machine Learning ◽  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Expansion Coefficient ◽  
Thermal Barrier Coating ◽  
Expansion Coefficient ◽  
Thermophysical Properties ◽  
Thermal Barrier ◽  
Coating Materials ◽  
Barrier Coating

Abstract It is a critical issue to reduce the thermal conductivity and increase the thermal expansion coefficient of ceramic thermal barrier coating (TBC) materials in the course of their utilization. To synthesize samples with different composition and measure their thermal conductivity by the traditional experimental approaches is time-consuming and expensive. Most classic and empirical models work inefficiently and inaccurately when researchers attempt to predict the thermophysical properties of TBC materials. In this research project, we tentatively exploit a Genetic Algorithm-Support Vector Regression (GA-SVR) machine learning model to study the thermophysical properties, illustrated with the potential TBC materials ZrO2 doped DyTaO4, which has resulted in the lowest thermal conductivity in rare earth tantalates RETaO4 system. Meanwhile, we employ statistical parameters of correlation coefficient (R2) and mean square error (MSE) to evaluate the accuracy and reliability of the model. The results reveal that this model has brought about high correlation coefficients of thermal conductivity and thermal expansion coefficient (99.8% and 99.9%, respectively), while the MSE values are 0.00052 and 0.00019, respectively. The doping concentration of ZrO2 was optimized to reach as low as 0.085-0.095, so as to reduce their thermal conductivity further and increase their thermal expansion. This model provides an accurate and reliable option for researchers to design ceramic thermal barrier coating materials.

Structural and mechanical properties of ternary MgCaSi phase: A study by density functional theory

2019 ◽  
Vol 44 (1-2) ◽  
pp. 50-59
Author(s):  
Rui Wu ◽  
Ya-Ping Wang ◽  
Yan Yang ◽  
Dong-Ming Luo ◽  
Hong Meng ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Density Functional Theory ◽  
Elastic Constants ◽  
Electronic Structures ◽  
Density Functional ◽  
Ternary Phase ◽  
Functional Theory ◽  
Young’S Moduli ◽  
Cauchy Pressure

The structural, elastic, and electronic properties of multi-performance ternary phase MgCaSi have been investigated by density functional theory. The present results show that MgCaSi is thermodynamically and mechanically stable. The derived elastic constants indicate that the c axis is the easiest to compress, followed by the a and b axes. The bulk, shear, and Young’s moduli of MgCaSi are higher than these of the mother phase Ca2Si, demonstrating that the hardness of MgCaSi has been favorably improved. The higher Debye temperature of MgCaSi also indicates stronger interatomic interactions and better thermal conductivity. Although MgCaSi exhibits less brittleness based on Pugh’s empirical formula, Poisson’s ratio, and the Cauchy pressure, orthorhombic MgCaSi possesses lower anisotropy than Ca2Si based on several criteria. To reveal the bonding nature of MgCaSi, the electronic structures are further investigated. It is found that the strong Si−Si bond plays a significant role for structural stability and elastic properties.

Electronic and optical response of HfO2: DFT calculations with Ti and Zr incorporation

2021 ◽  
pp. 2150452
Author(s):  
M. Junaid Iqbal Khan ◽  
Muhammad Yousaf ◽  
Shahid M. Ramay ◽  
Asif Mahmood ◽  
Hamid Ullah ◽  
...  
Keyword(s):  
Optical Properties ◽  
Density Functional ◽  
Perovskite Solar Cells ◽  
Visible Region ◽  
Optical Response ◽  
Semiconductor Materials ◽  
Generalized Gradient ◽  
Function Loss ◽  
Potential Applications ◽  
Photovoltaic Characteristics

Optical properties of semiconductor materials have been intensively studied for potential applications in perovskite solar cells. HfO2 is recently substituting the conventional semiconductor materials due to excellent photovoltaic characteristics. The electronic and optical properties of Ti- and Zr-incorporated HfO2 were investigated in this work using density functional theory. Ab-initio calculations were performed using Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (GGA). Electronic properties were studied by analyzing the band structure and density of states. Refractive index, attenuation coefficient, dielectric function, loss factor, energy loss spectra and absorption coefficient were calculated for the detailed study of optical response. A significant increase in absorption of HfO2 in the visible region with the incorporation of Ti revealed its important practicability in photovoltaic devices.

scholarly journals Structures, and Thermophysical Properties Characterizations of (La1-xHox)3NbO7 Solid Solutions as Thermal Barrier Coatings

2021 ◽  
Vol 8 ◽  
Author(s):  
Lin Chen ◽  
Yitao Wang ◽  
Qi Zheng ◽  
Jing Feng
Keyword(s):  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Solid Solutions ◽  
High Hardness ◽  
Lattice Stability ◽  
Low Thermal Conductivity ◽  
Thermal Expansion Coefficients ◽  
Anharmonic Lattice ◽  
Temperature Lattice ◽  
High Thermal Expansion

A sequence of (La1-xHox)3NbO7 solid solutions were fabricated in this work, which were studied as candidate for thermal insulation materials. The lattices were identified via XRD, when SEM and EDS were used to characterize the microstructures and element distributions. The results showed that the highest modulus, hardness, and toughness of (La1-xHox)3NbO7 were 196 GPa, 9.2 GPa, and 1.6 MPa m1/2, respectively, and they accorded with the mechanical property requirements. Also, a low thermal conductivity (1.06 W m−1 K−1) and high thermal expansion coefficients (TECs: 11.3 × 10−6 K−1) were simultaneously realized in (La3/6Ho3/6)3NbO7, at high temperatures. No phase transition was detected up to 1,200°C, which proved their good high-temperature lattice stability. The intense anharmonic lattice vibrations might contribute to the outstanding thermal properties of (La1-xHox)3NbO7 ceramics. The suitable modulus, high hardness, low thermal conductivity, and high TECs of (La1-xHox)3NbO7 solid solutions proclaimed that they were exceptional thermal insulation ceramics.

scholarly journals Attaining Low Lattice Thermal Conductivity in Half-Heusler Sublattice Solid Solutions: Which Substitution Site Is Most Effective?

2022 ◽  
Vol 3 (1) ◽  
pp. 1-14
Author(s):  
Rasmus Tranås ◽  
Ole Martin Løvvik ◽  
Kristian Berland
Keyword(s):  
Thermal Conductivity ◽  
Grain Boundary ◽  
Solid Solutions ◽  
Density Functional ◽  
Lattice Thermal Conductivity ◽  
Parent Compound ◽  
Combined Effect ◽  
Boundary Scattering ◽  
Heusler Compounds ◽  
Grain Boundary Scattering

Low thermal conductivity is an important materials property for thermoelectricity. The lattice thermal conductivity (LTC) can be reduced by introducing sublattice disorder through partial isovalent substitution. Yet, large-scale screening of materials has seldom taken this opportunity into account. The present study aims to investigate the effect of partial sublattice substitution on the LTC. The study relies on the temperature-dependent effective potential method based on forces obtained from density functional theory. Solid solutions are simulated within a virtual crystal approximation, and the effect of grain-boundary scattering is also included. This is done to systematically probe the effect of sublattice substitution on the LTC of 122 half-Heusler compounds. It is found that substitution on the three different crystallographic sites leads to a reduction of the LTC that varies significantly both between the sites and between the different compounds. Nevertheless, some common criteria are identified as most efficient for reduction of the LTC: The mass contrast should be large within the parent compound, and substitution should be performed on the heaviest atoms. It is also found that the combined effect of sublattice substitution and grain-boundary scattering can lead to a drastic reduction of the LTC. The lowest LTC of the current set of half-Heusler compounds is around 2 W/Km at 300 K for two of the parent compounds. Four additional compounds can reach similarly low LTC with the combined effect of sublattice disorder and grain boundaries. Two of these four compounds have an intrinsic LTC above ∼15 W/Km, underlining that materials with high intrinsic LTC could still be viable for thermoelectric applications.

scholarly journals Preparation and properties of CMAS resistant bixbyite structured high-entropy oxides RE2O3 (RE = Sm, Eu, Er, Lu, Y, and Yb): Promising environmental barrier coating materials for Al2O3f/Al2O3 composites

2021 ◽  
Vol 10 (3) ◽  
pp. 596-613 ◽  
Author(s):  
Yanan Sun ◽  
Huimin Xiang ◽  
Fu-Zhi Dai ◽  
Xiaohui Wang ◽  
Yan Xing ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Ceramic Matrix Composites ◽  
Mechanical And Thermal Properties ◽  
Coating Materials ◽  
Environmental Barrier ◽  
High Entropy ◽  
Thermal Expansion Coefficients ◽  
Environmental Barrier Coating ◽  
Barrier Coating

AbstractY2O3 is regarded as one of the potential environmental barrier coating (EBC) materials for Al2O3f/Al2O3 ceramic matrix composites owing to its high melting point and close thermal expansion coefficient to Al2O3. However, the relatively high thermal conductivity and unsatisfactory calcium-magnesium-aluminosilicate (CMAS) resistance are the main obstacles for the practical application of Y2O3. In order to reduce the thermal conductivity and increase the CMAS resistance, four cubic bixbyite structured high-entropy oxides RE2O3, including (Eu0.2Er0.2Lu0.2Y0.2Yb0.2)2O3, (Sm0.2Er0.2Lu0.2Y0.2Yb0.2)2O3, (Sm0.2Eu0.2Er0.2Y0.2Yb0.2)2O3, and (Sm0.2Eu0.2Lu0.2Y0.2Yb0.2)2O3 were designed and synthesized, among which (Eu0.2Er0.2Lu0.2Y0.2Yb0.2)2O3 and (Sm0.2Er0.2Lu0.2Y0.2Yb0.2)2O3 bulks were prepared by spark plasma sintering (SPS) to investigate their mechanical and thermal properties as well as CMAS resistance. The mechanical properties of (Eu0.2Er0.2Lu0.2Y0.2Yb0.2)2O3 and (Sm0.2Er0.2Lu0.2Y0.2Yb0.2)2O3 are close to those of Y2O3 but become more brittle than Y2O3. The thermal conductivities of (Eu0.2Er0.2Lu0.2Y0.2Yb0.2)2O3 and (Sm0.2Er0.2Lu0.2Y0.2Yb0.2)2O3 (5.1 and 4.6 W·m−1·K−1) are only 23.8% and 21.5% respectively of that of Y2O3 (21.4 W·m−1·K−1), while their thermal expansion coefficients are close to those of Y2O3 and Al2O3. Most importantly, HE RE2O3 ceramics exhibit good CMAS resistance. After being attacked by CMAS at 1350 °C for 4 h, the HE RE2O3 ceramics maintain their original morphologies without forming pores or cracks, making them promising as EBC materials for Al2O3f/Al2O3 composites.

scholarly journals Tuning the optoelectronic properties of hematite with rhodium doping for photoelectrochemical water splitting using density functional theory approach

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Abdur Rauf ◽  
Muhammad Adil ◽  
Shabeer Ahmad Mian ◽  
Gul Rahman ◽  
Ejaz Ahmed ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Optical Properties ◽  
Optical Absorption ◽  
Water Splitting ◽  
Density Functional ◽  
Formation Energy ◽  
Visible Region ◽  
Photoelectrochemical Water Splitting ◽  
Theory Approach ◽  
Functional Theory

AbstractHematite (Fe2O3) is one of the best candidates for photoelectrochemical water splitting due to its abundance and suitable bandgap. However, its efficiency is mostly impeded due to the intrinsically low conductivity and poor light absorption. In this study, we targeted this intrinsic behavior to investigate the thermodynamic stability, photoconductivity and optical properties of rhodium doped hematite using density functional theory. The calculated formation energy of pristine and rhodium doped hematite was − 4.47 eV and − 5.34 eV respectively, suggesting that the doped material is thermodynamically more stable. The DFT results established that the bandgap of doped hematite narrowed down to the lower edge (1.61 eV) in the visible region which enhanced the optical absorption and photoconductivity of the material. Moreover, doped hematite has the ability to absorb a broad spectrum (250–800) nm. The enhanced optical absorption boosted the photocurrent and incident photon to current efficiency. The calculated results also showed that the incorporation of rhodium in hematite induced a redshift in optical properties.

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