Biaxial Compressive Strain Research Articles

First Principles Study of Janus ZrClBr Monolayer Under Biaxial Strain

We have explored the structural, electronic, and thermoelectric properties of ZrClBr monolayer using density functional theory and semi-classical Boltzmann theory. The effect of biaxial compressive and tensile strains have been studied and compared. The band gap becomes narrow (broader) with compressive (tensile) strain as compared to that of unstrained ZrClBr monolayer. The electronic band structure is sensitive to the applied strain. The total and partial density of states have been explored. The ZrClBr monolayer is dynamically stable under the applied strain. The electronic transport coefficients are evaluated using BoltzTrap2 code under the constant relaxation time approximation. The Seebeck coefficient, electrical conductivity, and the power factor have been evaluated under both compressive and tensile at the different carrier concentrations of electrons and holes. The results show that the thermoelectric properties of ZrClBr monolayer can be tuned with the application of strain.

Tunable properties of the stable SiSeS Janus monolayer under biaxial strain: First-principles prediction

The electronic structure, optical and thermoelectric properties of Janus T-phase SiSeS monolayer under biaxial strain have been analyzed using the first-principles calculations. Our calculations identified the Janus T-phase SiSeS monolayer as an indirect semiconductor with an energy band gap of 0.77 eV at the equilibrium state, which can be tuned effectively through a biaxial strain. The band gap tends to decrease slowly when the large compression biaxial strains are applied. It is of interest that a semiconductor-metal phase transition was obtained under biaxial compression strain of − 8%. Moreover, the optical properties rise under biaxial strain with an enhanced absorption coefficient in the infrared region. Interestingly, the compressive biaxial strain combined with p-type doping in the Janus T-phase SiSeS monolayer produced a large electronic figure of merit (ZTe) of 7.0 at 300 K. The predicted results show the potential applications of Janus T-phase SiSeS monolayer for optoelectronic and thermoelectric devices.

Theoretical investigations of Janus WSeTe monolayer and related van der Waals heterostructures with promising thermoelectric performance

Recently, two-dimensional (2D) Janus MXY monolayers have received much attention due to their novel properties induced by the antisymmetric structures. In this work, the thermoelectric transport properties of the WSe2 and the Janus WSeTe monolayers are comparatively investigated based on first-principles calculations. The carriers of holes with higher mobility result in the better p-type power factor of WSeTe than WSe2. In addition, the broken of the mirror-asymmetry enhances the coupling strength between acoustic and optical branches and thus reduces the lattice thermal conductivity in WSeTe. The obtained ZT value of 1.53 is 5.9 times larger than that of WSe2 (0.26). Meanwhile, the thermoelectric performance of heterostructure MoSSe/WSeTe can be greatly enhanced by the biaxial compressive strain resulting from the band convergence. At the strain of −3%, the optimal ZT value of 1.62 is achieved for the p-type doped MoSSe/WSeTe at 300 K, which is 2.05 times higher than that of the unstrained structure. These results reveal that Janus monolayer WSeTe and its van der Waals heterostructure MoSSe/WSeTe are promising thermoelectric materials.

Tuning the Electronic and Optical Properties of the Novel Monolayer Noble-Transition-Metal Dichalcogenides Semiconductor β-AuSe via Strain: A Computational Investigation.

The strain-controlled structural, electronic, and optical characteristics of monolayer β-AuSe are systematically studied using first-principles calculations in this paper. For the strain-free monolayer β-AuSe, the structure is dynamically stable and maintains good stability at room temperature. It belongs to the indirect band gap semiconductor, and its valence band maximum (VBM) and conduction band minimum (CBM) consist of hybrid Au-d and Se-p electrons. Au–Se is a partial ionic bond and a partial polarized covalent bond. Meanwhile, lone-pair electrons exist around Se and are located between different layers. Moreover, its optical properties are anisotropic. As for the strained monolayer β-AuSe, it is susceptible to deformation by uniaxial tensile strain. It remains the semiconductor when applying different strains within an extensive range; however, only the biaxial compressive strain is beyond −12%, leading to a semiconductor–semimetal transition. Furthermore, it can maintain relatively stable optical properties under a high strain rate, whereas the change in optical properties is unpredictable when applying different strains. Finally, we suggest that the excellent carrier transport properties of the strain-free monolayer β-AuSe and the stable electronic properties of the strained monolayer β-AuSe originate from the p–d hybridization effect. Therefore, we predict that monolayer β-AuSe is a promising flexible semiconductive photoelectric material in the high-efficiency nano-electronic and nano-optoelectronic fields.

Electronic and magnetic properties of silicene monolayer under bi-axial mechanical strain: First principles study

Mechanical control of electronic and magnetic properties of 2D Van-der-Waals heterostructures gives new possibilities for further development of spintronics and information-related technologies. Using the density functional theory, we investigate the structural, electronic and magnetic properties of silicene monolayer with substituted Chromium atoms and under a small biaxial strain (−6%<ε<8%). Our results indicate that the Cr-doped silicene nanosheets without strain have magnetic metallic, half-metallic or semiconducting properties depending on the type of substitution. We also show that the magnetic moments associated with the monomer and vertical dimer substitutions change very weakly with strain. However, the magnetic moment associated with the horizontal dimer substitution decreases when either compressive or tensile strain is applied to the system. Additionally, we show that the largest semiconductor band-gap is approximately 0.13 eV under zero strain for the vertical Cr-doped silicene. Finally, biaxial compressive strain leads to irregular changes in the magnetic moment for Cr vertical dimer substitution.

Structural and optical properties of a layered ε-GaSe thin film under elastic deformation from flexible PET substrate

The present study focuses on the structural and optical characterizations of a GaSe thin-film consisting of few layers mechanically exfoliated from bulk GaSe on a flexible PET substrate. The XRD and the RAMAN spectroscopies confirm the high crystallinity of our material and show that it belongs to the hexagonal ε-GaSe polytype with a mean crystallite size of about 50 ​nm. The sample’s SEM images exhibit the two-dimensional nature of the layers. The optical transmission measurements clearly show two absorbing edges. They were assigned to an indirect band gap at 1.92 ​eV and to a direct one at 2.2 ​eV. The appreciable difference between the two gaps, of about 0.28 ​eV, is attributed to a compressive biaxial strain. A value, as high as 104 ​cm−1, of the absorption coefficient has been obtained which demonstrates the GaSe material’s great potential for optoelectronic applications.

Strain-induced electronic and optical properties of inorganic lead halide perovskites APbBr3 (A= Rb and Cs)

Recently, inorganic perovskite materials have been achieved with broad consideration in photovoltaic technology owing to their exceptional structural, electronic, and optical properties. This work comprehensively studied the impact of the biaxial compressive and tensile strain on the structural, electronic, and optical properties of the inorganic halide perovskites APbBr3 (A= Rb and Cs) using the first-principles density-functional theory (FP-DFT). This study also initiated to recognize the function of the A-cation on the structural, electronic, and optical properties of the inorganic perovskites. The electronic band structures show that RbPbBr3 and CsPbBr3 are semiconductor materials with a direct bandgap of 1.31 eV and 1.68 eV at the R-point. When considering the spin-orbital coupling (SOC) relativistic effect, the bandgap of the RbPbBr3 and CsPbBr3 perovskites is reduced to 0.282 and 0.478 eV, respectively. Moreover, the bandgap of all the structures shows a reducing trend when the compressive strain is applied and an increasing trend when the tensile strain is introduced. Optical properties like dielectric functions, absorption coefficient, and electron loss function show that these materials have good absorption ability in the visible region due to their band properties. It is found that the peaks of the dielectric constant of APbBr3 (A= Rb and Cs) shift to lower photon energy (redshift) when increasing compressive strain, and in contrast, they show higher photon energy shifting nature (blueshift) when enhancing tensile strain. Therefore, these properties make the APbBr3 (A= Rb and Cs) perovskites very appropriate to apply in light management of solar cells and energy storage devices.

Electronic Structures of Group III–V Element Haeckelite Compounds: A Novel Family of Semiconductors, Dirac Semimetals, and Topological Insulators

AbstractThe family of III–V element compounds (i.e., XY compounds; X = B, Al, Ga, In, or Tl; Y = N, P, As, or Sb) have been intensively investigated for several decades because of their enormous applications for many optoelectronic devices. Here, by employing first‐principles calculations, the electronic structures of bulk XY haeckelite compounds are examined. It is identified that InSb (TlN and TlP) is Dirac semimetal (are strong topological insulators). The other fifteen XY compounds are semiconducting. The effect of biaxial and uniaxial tensile and compressive strains on the electronic structures are studied. These materials offer diverse topological orders. The semiconducting band gaps are mainly found between the bonding and antibonding states of the mixed X(p)–Y(p) orbitals at the top of the valence band and the bottom of the conduction bands, respectively. The topological insulating nature of the XY compounds is explained based on the degenerate px + py orbitals and their orbital energies relative to the pz orbitals near the Fermi energy. The nontrivial band topologies of TlN and TlP are confirmed by calculating the Z2 (1;000) index, surface states, and Wilson loop calculations. The bands split into two branches by including spin‐orbit interaction. The results demonstrate that haeckelite compounds are fascinating materials with broad potential applications in optoelectronics and possessing the possibility of hosting emergent physical phenomena.

Influence of Al x Ga1−x N nucleation layers on MOVPE-grown zincblende GaN epilayers on 3C-SiC/Si(001)

The suitability of Al x Ga1−x N nucleation layers (NLs) with varying Al fraction x for the metal organic vapour phase epitaxy of zincblende GaN on (001) 3C-SiC was investigated, using x-ray photoelectron spectroscopy, atomic force microscopy, and x-ray diffraction. The as-grown NLs exhibited elongated island structures on their surface, which reduce laterally into smaller, more equiaxed islands with increasing AlN composition. During high-temperature annealing in a mixture of NH3 and H2 the nucleation islands with low Al fraction ripened and increased in size, whereas this effect was less pronounced in samples with higher Al fraction. The compressive biaxial in-plane strain of the NLs increases with increasing AlN composition up to x = 0.29. GaN epilayers grown over NLs that have low Al fraction have high cubic zincblende phase purity and are slightly compressively strained relative to 3C-SiC. However, those samples with a measured Al fraction in the NL higher than 0.29 were predominantly of the hexagonal wurtzite phase, due to formation of wurtzite inclusions on various {111} facets of zb-GaN, thus indicating the optimal Al composition for phase-pure zb-GaN epilayer growth.

Strain modulation of electronic and optical properties of monolayer MoSi2N4

The strain engineering is an important approaches to modulate the electronic and optical properties of materials . Recently, a new two dimensional material monolayer MoSi 2 N 4 has been successfully synthesized with excellent electronic performance. The electronic properties of monolayer MoSi 2 N 4 without and with in-plane strain are systematically investigated by first-principles calculation. The calculation results reveal monolayer MoSi 2 N 4 is an indirect bandgap semiconductor with bandgap 1.74 eV (PBE) and 2.31 eV (HSE06), but it can be transformed to a direct bandgap under the certain in-plane strain, such as 3% and 4% biaxial compressive strain. In-plane strain can effectively modulate the band structure, bandgap, and the carrier effective mass. Furthermore, the optical properties of unstrained and transformed to direct bandgap situations are calculated. The light absorption capacity of monolayer MoSi 2 N 4 is stronger in the ultraviolet band, and can be changed when it is transformed to a direct bandgap. The electrical and optical properties can be modulated by strain engineering, making it is a promising candidate of strain-modulated optoelectronic devices . • The electronic and optical properties of monolayer MoSi 2 N 4 under in-plane strain are studied. • Biaxial compressive strain can transform the energy band from a direct bandgap to an indirect bandgap. • In-plane strain can modulate the hole effective mass. • MoSi 2 N 4 has an excellent light absorption performance in the ultraviolet region.

Two dimensional twin T-graphene: monolayer for visible-light photocatalytic water splitting and bulk for anode material of magnesium batteries.

Two-dimensional (2D) carbon allotropes with all-sp2-hybridization have demonstrated great potential in nano-photoelectric devices, but the application of semiconductor photocatalysts for water splitting and anodes in magnesium batteries remains unoptimistic. Motivated by this, we theoretically study a highly stable all-sp2-hybridized 2D carbon allotrope twin T-graphene (TTG) via first-principles simulations. And through the calculations of the HSE06 functional, we find that TTG has a wide bandgap (2.70 eV) and suitable band edge positions satisfying the criteria of photocatalysts for overall water splitting. Additionally, TTG exhibits excellent photocatalytic properties for overall water splitting reflecting a high STH efficiency (12.34%), strong absorption coefficient in the visible-light region and the carrier mobility being high for electrons but low for holes. By investigating the strain effects, we get that, with biaxial compressive strain, the ability of overall photocatalytic water splitting can be effectively improved including STH up to ∼30%. Moreover, the bulk TTG also exhibits great potential as an anode material of magnesium batteries with a theoretical capacity of 556 mA h g-1, average voltage of 0.74 V and diffusion energy barrier of ∼0.96 eV. Our results would broaden the application of all-sp2-hybridized 2D carbon allotropes in the semiconductor photocatalytic and magnesium batteries field.

First-principles study of strain-tunable charge carrier transport properties and optical properties of CrI&lt;sub&gt;3&lt;/sub&gt; monolayer

Because the single-layer CrI&lt;sub&gt;3&lt;/sub&gt; is a half semiconductor with indirect band gap and magnetic anisotropy, it has received much attention in the spintronic, magneto-electronic and magnetic storage applications. However, the knowledge of the dependence of carrier mobility and optical property on strain is still rather limited. The uniaxial and biaxial strain dependence of electronic, transport, optical and magnetic properties of single-layer CrI&lt;sub&gt;3&lt;/sub&gt; are systematically investigated by using first-principles calculations, and the results are compared with experimental results. The electronic structures under different strains are first calculated by using the accurate HSE06 functional, then the carrier mobility is estimated by the deformation potential theory and the dielectric function is obtained to estimate the optical absorption especially in the visible light range. Finally, the magnetic anisotropy energy used to estimate the magneto-electronic properties is studied by the Perdew-Bueke-Ernzerhof functional including the spin-orbit coupling. It is found that the ferromagnetic CrI&lt;sub&gt;3&lt;/sub&gt; is an indirect and half semiconductor with band gap 2.024 eV,&lt;inline-formula&gt;&lt;tex-math id="M1"&gt;\begin{document}$ \Delta {\text{CBM}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20221019_M1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20221019_M1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;= 1.592 eV, &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$ \Delta {\text{VBM}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20221019_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20221019_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;= 0.238 eV and can be driven into AF-Néel antiferromagnetic phase by applying –6% to –8% (compressive) biaxial stain, exhibiting excellent agreement with the results from the literature. It is found that of single-layer CrI&lt;sub&gt;3&lt;/sub&gt; has very low carrier mobility with a value within 10 cm&lt;sup&gt;2&lt;/sup&gt;·V&lt;sup&gt;–1&lt;/sup&gt;·s&lt;sup&gt;–1&lt;/sup&gt; due to the large effective mass and small in-plane stiffness can be remarkably increased by increasing biaxial compression strain attributed to the reduced effective mass. A high electron mobility 174 cm&lt;sup&gt;2&lt;/sup&gt;·V&lt;sup&gt;–1&lt;/sup&gt;·s&lt;sup&gt;–1&lt;/sup&gt; is obtained in the zigzag direction by applying a –8% biaxial strain reaching the level of monolayer MoS&lt;sub&gt;2&lt;/sub&gt;. The calculated imaginary component of dielectric function along the &lt;i&gt;x &lt;/i&gt;(&lt;i&gt;y&lt;/i&gt;) direction having two peaks (I, II) in the visible light range is obviously different from that along the &lt;i&gt;z&lt;/i&gt; direction, indicating that the single-layer CrI&lt;sub&gt;3&lt;/sub&gt; has optical anisotropy, demonstrating the good agreement with results from the literature. It is found that the imaginary part of dielectric function shows that an obvious redshift and peak (I, II) values strongly increase with the increase of compressive strain (biaxial), showing good agreement with the calculated electronic structures and indicating that monolayer CrI&lt;sub&gt;3&lt;/sub&gt; possesses high optical adsorption of visible light under a compressive biaxial strain. Furthermore, it is found that the magnetic anisotropy energy of monolayer CrI&lt;sub&gt;3&lt;/sub&gt; mainly stemming from the orbital magnetic moment of Cr ions remarkably increases from 0.7365 to 1.08 meV/Cr with g compressive strain increasing. These results indicate that the optoelectronic property of single-layer CrI&lt;sub&gt;3&lt;/sub&gt; can be greatly improved by applying biaxial compressive strain and the single-layer CrI&lt;sub&gt;3&lt;/sub&gt; is a promising material for applications in microelectronic, optoelectronic and magnetic storage.

Electronic and transport property of two-dimensional boron phosphide sheet

Using density functional theory (DFT) approach, we have investigated the effect of strain on the electronic properties of two-dimensional (2D) boron phosphide (BP) sheet. With the increase in uniaxial and biaxial tensile strain band gap increases while band gap decreases and becomes metallic with the increase in uniaxial and biaxial compressive strain. Electrical and thermal transport properties of zigzag and armchair 2D BP sheets have been explored using nonequilibrium Green's function formalism (NEGF) and the changes in the nature of I–V characteristics with the application of strain have been reported. The magnitude of the current decreases with the increase of strain value along transport direction for both zigzag and armchair 2D BP sheets. For unstrained systems, the magnitude of current is nearly same for both zigzag and armchair 2D BP sheets. However, for a particular strain value, magnitude of current is more for zigzag sheet compared to armchair sheet. Though both zigzag and armchair 2D BP sheets have reasonably high ZTe which confirms its potentiality for designing efficient thermoelectric material but zigzag sheet is more preferable for thermoelectric application compared to armchair sheet due to its higher ZTe in comparison to armchair sheet.

Tuning the magnetocaloric effect by optimizing thickness-induced three-dimensional strain states

The effect of 3-dimensional strain state on the magnetocaloric properties of epitaxial La0.8Ca0.2MnO3 (LCMO) thin films grown on two types of substrates, SrTiO3 (001) (STO) and LaAlO3 (001) (LAO) has been studied as a function of film thickness within the range of 25 to 300 nm. The STO substrate imposes an in-plane tensile biaxial strain while LAO substrate imposes an in-plane compressive biaxial strain. The in-plane biaxial strain on LCMO by STO substrate gets relaxed more rapidly than that by LAO substrate but both LCMO/STO and LCMO/LAO show a maximum entropy change of 12.1 J/Kg-K and 3.2 J/Kg-K, respectively at a critical thickness of 75 nm (at 6 T applied magnetic field). LCMO/LAO is found to exhibit a wider transition temperature region with full width at half maxima (FWHM) 40 K of the dM/dT vs T curve compared to LCMO/STO with FWHM 33 K of that curve. This broadening of the transition region indicates that the Table like magnetocaloric effect (MCE) is attainable by changing the strain type. The maximum Relative Cooling Power, 361 J/Kg of LCMO/STO and 339 J/Kg of LCMO/LAO is also observed at the thickness 75 nm. The Curie temperature varies with the thickness exploring the variation of ferromagnetic interaction strength due to strain relaxation. The film thickness and substrate induced lattice strain are proved to be the significant parameters for controlling MCE. The highest MCE response at a particular thickness shows the possibility of tuning MCE in other devices by optimizing thickness.

MXene monolayer Mn2ZnN2: a promising robust intrinsic half-metallic nanosheet

Two-dimensional half-metallic ferromagnets are promising in spintronics. In recent years, the half-metallicity and the magnetic properties of the MXene materials have been the research hotspots of new materials due to their unique crystal characteristics and wide applications. In this paper, the MXene nanosheet Mn2ZnN2 was predicted as a kind of robust intrinsic half-metallic nanosheet whose magnetic moment per unit is the integer 6.00 μ B based on the first principles calculations. The half-metallic character and the magnetic moment of this nanosheet mainly result from the spin-polarized Mn-ions induced by the crystal field. If the absolute biaxial compression strain is lower than 3.0%, the half-metallicity remains well and the magnetic moment per unit is always 6.00 μ B, indicating that its half-metallicity and magnetic properties are stable within a certain pressure range. More importantly, the magnetic moment per unit is elevated from 6.00 μ B to 9.00 μ B and the half-metallic energy gap increases evidently after an electron is removed from this nanosheet, suggesting that the half-metallicity and magnetic properties of this nanosheet may be improved via tuning its charge state.

Engineering the hydrogen storage properties of the perovskite hydride ZrNiH3 by uniaxial/biaxial strain

In the present work, the bonding length, electronic structure, stability, and dehydrogenation properties of the Perovskite-type ZrNiH3 hydride, under different uniaxial/biaxial strains are investigated through ab-initio calculations based on the plane-wave pseudo-potential (PW-PP) approach. The findings reveal that the uniaxial/biaxial compressive and tensile strains are responsible for the structural deformation of the ZrNiH3 crystal structure, and its lattice deformation becomes more significant with decreasing or increasing the strain magnitude. Due to the strain energy contribution, the uniaxial/biaxial strain not only lowers the stability of ZrNiH3 but also decreases considerably the dehydrogenation enthalpy and decomposition temperature. Precisely, the formation enthalpy and decomposition temperature are reduced from −67.73 kJ/mol.H2 and 521 K for non-strained ZrNiH3 up to −33.73 kJ/mol.H2 and 259.5 K under maximal biaxial compression strain of ε = −6%, and to −50.99 kJ/mol.H2 and 392.23 K for the maximal biaxial tensile strain of ε = +6%. The same phenomenon has been also observed for the uniaxial strain, where the formation enthalpy and decomposition temperature are both decreased to −39.36 kJ/mol.H2 and 302.78 K for a maximal uniaxial compressive strain of ε = - 12%, and to −51.86 kJ/mol.H2 and 399 K under the maximal uniaxial tensile strain of ε = +12%. Moreover, the densities of states analysis suggests that the strain-induced variation in the dehydrogenation and structural properties of ZrNiH3 are strongly related to the Fermi level value of total densities of states. These ab-initio calculations demonstrate insightful novel approach into the development of Zr-based intermetallic hydrides for hydrogen storage practical applications.

Orbital−energy splitting in Ruddlesden−Popper layered halide perovskites for tunable optoelectronic properties

The electronic orbital characteristics at the band edges play an important role in determining the electrical, optical and defect properties of perovskite photovoltaic materials. It is highly desirable to establish the relationship between the underlying atomic orbitals and the optoelectronic properties as a guide to maximize the photovoltaic performance. Here, using first-principles calculations and taking Ruddlesden-Popper (RP) phase layered perovskites Cs n +1 Ge n I n +1 Cl 2n as examples, we demonstrate how to rationally optimize the optoelectronic properties (e.g., band gap, transition dipole matrix elements, carrier effective masses, bandwidth) through a simple band structure parameter. Our results show that reducing the splitting energy |Δ c | between the in-plane p x , y and out-of-plane p z orbitals at the conduction band minimum (CBM) can effectively reduce the band gap and carrier effective masses while greatly improving the optical absorption in the visible region. Thereby, the orbital-property relationship with Δ c is well established through biaxial compressive strain. Finally, it is shown that this approach can be reasonably extended to several other non-cubic halide perovskites with similar p orbitals characteristics at the conduction band edge. Therefore, we believe that our proposed orbital engineering approach will provide atomic-level guidance for understanding the performance limits of layered perovskite solar cells. • Orbital−energy splitting in Ruddlesden−Popper layered halide perovskites. • Optimizing the optoelectronic properties through a simple band structure parameter. • Reducing the splitting energy .|Δ c | can effectively tune the optoelectronic properties.

Photoelectric properties and stability of the single-layer transition metal dichalcogenides under three stress states

In this paper, the electrical and optical properties of single-layer MoS2 and single-layer WS2 in three strain states: biaxial tension, biaxial compression, biaxial tension and compression are systematically studied. All calculations are based on the first-principle of density functional theory. The results show that after biaxial tension strain, biaxial compression strain, and biaxial tension-compression strain are applied, the atomic structure, energy band structure, and optical absorption coefficient will show disparate changing trends. When the biaxial tension and compression strain intensity is less than 15%, the bond length, bond angle, and light absorption peak will have little fluctuation with the increase of strain intensity. However, compared with the other two strain states, these two crystal structures are the most volatile at this time. In addition, when 15% biaxial tensile strain is applied, the two crystals can still maintain their kinetic stability.

Strain tailored thermodynamic stability, electronic transitions, and optoelectronic properties of III (In, Ga and Al)-nitride monolayers

The thermodynamic stability of III-nitride monolayers is calculated using the phonon band structure. Electronic properties are computed using the generalized gradient approximation-Perdew–Burke–Ernzerhof exchange-correlation potentials, which show the semiconducting behavior with bandgap 0.59 eV, 2.034 eV, and 2.906 eV for InN, GaN, and AlN monolayers, respectively. The biaxial tensile and compressive strains are used as external stimuli to understand their impact on the optoelectronic properties of these monolayers. The thermodynamic stability of strained monolayers is investigated to explore the maximum possible strains, i.e. flexibility limit, these monolayers can sustain. These monolayers are more sensitive to compressive strains, showing thermodynamic instability even at 1% compressive strain for all the considered monolayers. Further, the III-nitride monolayers are more robust with the tensile strain. InN, GaN, and AlN monolayers can sustain up to 4%, 16%, and 18% tensile strain, respectively. More interestingly, the electronic transitions, such as direct to indirect and semiconducting to metallic, are noticed with strain in the considered monolayers. The optical properties also exhibit strong strain dependency at the different transition points.

Predicted double perovskite material Ca2ZrTiO6 with enhanced n-type thermoelectric performance

Herein, using first-principles calculations, we studied the electronic and thermoelectric properties of isolated perovskites CaTiO3, CaZrO3 and double perovskite Ca2ZrTiO6 crystal structure under ambient conditions, biaxial compression, and biaxial tensile strain. We used generalized gradient approximation and the Hubbard parameter (GGA ​+ ​U) to calculate exchange and correlation interactions. The isolated perovskite CaTiO3 and CaZrO3 are indirect bandgap (Γ ​− ​R) semiconductors of values 1.90 ​eV, 3.2 ​eV, respectively. The construction of a double perovskite Ca2ZrTiO6 results in a direct (Γ ​− ​Γ) bandgap semiconductor material. The bandgap values under 2% & 5% biaxial tensile strain and compressive strain are in the range of 2.3 ​eV and 2.2 ​eV. We studied the thermoelectric properties by taking the two chemical potential values (μ) equal to CBM and VBM, respectively. The thermoelectric properties of Ca2ZrTiO6 under 2% & 5% biaxial tensile strain were improved at CBM, while thermoelectric properties under 2% & 5% biaxial compression strain were enhanced at VBM as compared to thermoelectric properties under ambient conditions. At CBM, the maximum value of the figure of merit (ZT) is about 4.4 ​at 500 ​K, required for the next generation of the thermoelectric device. The ZT value shows that the novel double perovskite is a very suitable candidate for thermoelectric devices.