arXiv subjects

Saswata Bhattacharya

Publications and source records attributed to Saswata Bhattacharya.

At least 37 records · Page 2Linked to original sources

arXiv2023

Multiple Zeeman-type Hidden Spin Splitting in $\mathcal{\hat{P}\hat{T}}$-Symmetric Layered Antiferromagnets

Centrosymmetric antiferromagnetic semiconductors, although abundant in nature, appear less favorable in spintronics owing to the lack of inherent spin polarization and magnetization. We unveil hidden Zeeman-type spin splitting (HZSS) in layered centrosymmetric antiferromagnets with asymmetric sublayer structures by employing first-principles simulations and symmetry analysis. Taking the bilayer counterpart of recently synthesized monolayer MnSe, we demonstrate that the degenerate states around specific high-symmetry points spatially segregate on different sublayers forming PT-symmetric pair. Furthermore, degenerate states exhibit uniform in-plane spin configurations with opposite orientations enforced by mirror symmetry. Bands are locally Zeeman-split up to order of 70 meV. Strikingly, a tiny electric field of a few mVA-1 along the z-direction breaks the double degeneracy forming additional Zeeman pair. Moreover, our simulations on trilayer and tetralayer MnSe show that achieved HZSS is independent of layer number. These findings establish the design principle to obtain Zeeman-type splitting in centrosymmetric antiferromagnets and significantly expand the range of materials to look for spintronics.

cond-mat.mtrl-sci↗

arXiv2023

Vacancy-Ordered Double Perovskites Cs$_2$BI$_6$ (B = Pt, Pd, Te, Sn): An Emerging Class of Thermoelectric Materials

Vacancy-ordered double perovskites (A$_2$BX$_6$), being one of the environmentally friendly and stable alternatives to lead halide perovskites, have garnered considerable research attention in the scientific community. However, their thermal transport has not been explored much despite their potential applications. Here, we explore Cs$_2$BI$_6$ (B = Pt, Pd, Te, Sn) as potential thermoelectric materials using the state-of-the-art first-principles based methodologies, viz., density functional theory combined with many-body perturbation theory (G$_0$W$_0$) and spin-orbit coupling. %The phonon dispersion plots and Poisson's and Pugh's ratios show the dynamical and mechanical stability of this class of perovskites. The absence of polyhedral connectivity in vacancy-ordered perovskites gives rise to additional degrees of freedom leading to lattice anharmonicity. The presence of anharmonic lattice dynamics leads to strong electron-phonon coupling, which is well captured by Fröhlich mesoscopic model. % to investigate the interaction of longitudinal optical phonon modes with the carriers that strongly influence the carrier mobility. The lattice anharmonicity is further studied using {\it ab initio} molecular dynamics and electron localization function. The maximum anharmonicity is observed in Cs$_2$PtI$_6$, followed by Cs$_2$PdI$_6$, Cs$_2$TeI$_6$ and Cs$_2$SnI$_6$. Also, the computed average thermoelectric figure of merit ($zT$) for Cs$_2$PtI$_6$, Cs$_2$PdI$_6$, Cs$_2$TeI$_6$ and Cs$_2$SnI$_6$ are 0.88, 0.85, 0.95 and 0.78, respectively, which reveals their promising renewable energy applications.

cond-mat.mtrl-sci↗

arXiv2023

Strain-driven topological quantum phase transition in the family of halide perovskites

The centrosymmetric halide perovskites undergo a continuous phase transition from a normal insulator to a topological insulator at the critical value of strain. Contrarily, in noncentrosymmetric halide perovskites, this phase transition is discontinuous. The noncentrosymmetry does not stabilize the gapless state, causing a discontinuity in the bandgap. We have employed the density functional theory and Slater-Koster formalism-based tight-binding Hamiltonian studies to understand the evolution of band topology under the compressive strain in the halide perovskites. Our study shows that both cubic and pseudocubic FAPbI$_3$ undergo a Pb $\textit{s-p}$ band inversion at $γ$ (V/V$_0$) = 0.76 and 0.73, respectively. The cubic perovskite shows the surface state at $\overline{M}$, whereas, the pseudocubic structure shows two conducting states in the neighbourhood of $\overline{M}$, unlike the conventional topological insulator. The Pb-Pb second nearest neighbor interactions determine this topological phase transition. Alongside, we have modeled mixed cation halide perovskites Cs$_x$MA$_{1-x}$PbI$_3$ (\textit{x} = 0.25, 0.5 and 0.75) to study their topological properties. Cs$_{0.5}$MA$_{0.5}$PbI$_3$ shows non-trivial topology at $γ$ = 0.74. In addition, we have checked the structural stability of different strained configurations using ab \textit{initio} molecular dynamics at operational temperature. Their structural stability under compression strengthens the experimental relevance.

cond-mat.mtrl-sci↗

arXiv2023

Probing the uniaxial strain-dependent valley drift and Berry curvature in monolayer MoSi$_2$N$_4$

We use ab initio calculations and theoretical analysis to investigate the influence of in-plane strain field on valley drifts and Berry curvatures in the monolayer MoSi$_2$N$_4$, a prototypical septuple atomic layered two-dimensional material. The low energy electron and hole valleys drift far off the K/K' point under uniaxial strains. The direction and strength of valley drift strongly depend on the nature of the charge carrier and uniaxial strain with a more substantial response along the zigzag path. Our findings are governed by the interplay between microscopic orbital contribution and symmetry lowering. The changing geometric properties of Bloch states affect the Berry curvatures and circular dichroism. Specifically, Berry curvature dipole is significantly enhanced under the tensile strain along armchair and zigzag directions. Meanwhile, the particle-hole asymmetry arising from non-equivalent electron and hole valley drifts relax the selection rules, thus reducing the degree of circular polarization up to ~0.98. Therefore, strain engineering of valley physics in the monolayer MoSi$_2$N$_4$ is of prime importance for valleytronics.

cond-mat.mtrl-sci↗

arXiv2023

Manipulation of valley and spin properties in two-dimensional Janus WSiGeZ$_4$ (Z=N,P, As) through symmetry control

A class of septuple-atomic-layer two-dimensional (2D) materials, MA$_2$Z$_4$, is sought as an alternative to 2D hexagonal transition metal dichalcogenides in the field of valleytronics and spintronics. In these materials, the structural symmetry can be varied by changing the stacking of its three parts in the monolayer. We show that in Janus monolayer WSiGeZ$_4$ (Z=N, P, As), the Berry curvature and Rashba effect are enhanced by modifying the stacking orders. Intrinsic electric field and composition of the d orbitals play a dominant role in determining these properties. The vertical field lifts the spin degeneracy along in-plane direction, inducing the Rashba effect around $Γ$ point. The in-plane orbitals under the influence of in-plane electric field contribute to the Zeeman splitting of bands at K/K' points. Berry curvature is strengthened by up to 300% compared to its ground state through symmetry control, along with a significant increment in the Rashba coefficient. Moreover, monolayer WSiGeP$_4$ and WSiGeAs$_4$ have multiple valleys, implying another valley-dimension. We construct a symmetry adapted k.p Hamiltonian for the valleys and investigate the effect of strain and electric field on the band structure. The interesting spin-valley physics in monolayer WSiGeZ$_4$ suggests their exceptional potential for spintronics and valleytronics applications.

cond-mat.mtrl-sci↗

arXiv2023

Effect of crystal field engineering and Fermi level optimization on thermoelectric properties of Ge$_{1.01}$Te: Experimental investigation and theoretical insight

This study shows a method of enhancing the thermoelectric properties of GeTe-based materials by Ti and Bi co-doping on cation sites along with self-doping with Ge via simultaneous optimization of electronic (via crystal field engineering, and precise Fermi level optimization) and thermal (via point-defect scattering) transport properties. The pristine GeTe possesses high carrier concentration ($n$) due to intrinsic Ge vacancies, low Seebeck coefficient ($α$), and high thermal conductivity ($κ$). The Ge vacancy optimization and crystal field engineering results in an enhanced $α$ via excess Ge and Ti doping, which is further improved by band structure engineering through Bi doping. As a result of improved $α$ and optimized Fermi level (carrier concentration), an enhanced power factor ($α^2σ$) is obtained for Ti--Bi co-doped Ge$_{1.01}$Te. These experimental results are also evidenced by theoretical calculations of band structure, and thermoelectric parameters using density functional theory and Boltztrap calculations, respectively. A significant reduction in the phonon thermal conductivity ($κ_{ph}$) from $\sim$ 3.5 W.m$^{-1}$.K$^{-1}$ to $\sim$ 1.06 W.m$^{-1}$.K$^{-1}$ at 300\,K for Ti--Bi co-doping in GeTe, attributed to point-defect scattering due to mass and strain field fluctuation, in line with the Debye-Callaway model. The phonon dispersion calculations show a decreasing group velocity in Ti--Bi co-doped GeTe, supporting the obtained reduced $κ_{ph}$. The strategies used in the present study can significantly increase the effective mass, optimize the carrier concentration, and decrease phonon thermal conductivity while achieving an impressive maximum zT value of 1.75 at 773\,K and average zT (zT$_{av}$) of 1.03 for Ge$_{0.91}$Ti$_{0.02}$Bi$_{0.08}$Te over a temperature range of 300-773\,K.

cond-mat.mtrl-sci↗

arXiv2023

Theoretical evaluation of oxynitride, oxyfluoride and nitrofluoride perovskites with promising photon absorption properties for solar water splitting

Photocatalytic water splitting represents a very promising but at the same time very challenging contribution to a clean and renewable route to produce hydrogen fuel. Developing efficient and cost-effective photocatalysts for water splitting is a growing need. For this purpose, semiconductor photocatalysts have attracted much more attention due to their stability and low manufacturing cost. Here, we have systematically applied several state-of-the-art advanced first-principles-based methodologies, viz., hybrid density functional theory, many-body perturbation theory (G$_0$W$_0$) and density functional perturbation theory (DFPT), to understand the electronic structure properties of ABX$_2$Y perovskites. We have chosen the vast composition space of ABX$_2$Y type perovskites where A and B are cations and X and Y can be nitrogen, oxygen, or fluorine. These perovskites exhibit direct band gaps ranging from 1.6 to 3.3 eV. Further, to evaluate the feasibility of the visible light catalytic performance, we calculate the structural, electronic, and optical properties of ABX$_2$Y perovskites. In addition, from hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) mechanism, BaInO$_2$F, InSnO$_2$N, CsPbO$_2$F and LaNbN$_2$O are found as probable photocatalysts.

cond-mat.mtrl-sci↗

arXiv2022

Electrocatalytic Study for Hydrogen Evolution Reaction on MoS$_2$/BP and MoSSe/BP in Acidic Media

Molecular hydrogen (H$_2$) production by electrochemical hydrogen evolution reaction (HER) is being actively explored for non-precious-metal based electrocatalysts that are earth-abundant and low cost like MoS$_2$. Although it is acid-stable, its applicability is limited by catalytically inactive basal plane, poor electrical transport and inefficient charge transfer at the interface. Therefore, the present work examines its bilayer van der Waals heterostructure (vdW HTS). The second constituent monolayer Boron Phosphide (BP) is advantageous as an electrode material owing to its chemical stability in both oxygen and water environments. Here, we have performed first-principles based calculations under the framework of density functional theory (DFT) for HER in an electrochemical double layer model with the BP monolayer, MoS$_2$/BP and MoSSe/BP vdW HTSs. The climbing image nudged elastic band method (CI-NEB) has been employed to determine the minimum energy pathways for Tafel and Heyrovsky reactions. The calculations yield that Tafel reaction shows no reaction barrier. Thereafter, for Heyrovsky reaction, we have obtained low reaction barrier in the vdW HTSs as compared to that in the BP monolayer. Subsequently, we have observed no significant difference in the reaction profile of MoS$_2$/BP and MoSSe/BP vdW HTSs in case of high coverage (25 %) and 1/3 H$^+$ concentration (conc.). However, in the case of small coverage (11 %) and 1/3 H$^+$ conc., MoSSe/BP shows feasible Heyrovsky reaction with no reaction barrier. Finally, on comparing the coverages with 1/4 H$^+$ conc., we deduce high coverage with low conc. and low coverage with high conc. to be apt for HER via Heyrovsky reaction path.

cond-mat.mtrl-sci↗

arXiv2022

Coupled spin-valley, Rashba effect and hidden persistent spin polarization in WSi$_2$N$_4$ family

The new two-dimensional materials, MoSi$_2$N$_4$ and WSi$_2$N$_4$ are experimentally synthesized successfully and various similar structures are predicted theoretically. Here, we report the electronic properties with a special focus on the band splitting in WA$_2$Z$_4$ (A=Si, Ge; Z=N, P, As), using state-of-the-art density functional theory and many-body perturbation theory (within the framework of G$_0$W$_0$ and BSE). Due to the broken inversion symmetry and strong spin-orbit coupling effects, we detect coupled spin-valley effects at the corners of the first Brillouin zone (BZ). Additionally, we observe cubically and linearly split bands around the $Γ$ and M points, respectively. Interestingly, the in-plane mirror symmetry ($σ_h$) and the reduced symmetry of arbitrary $k$-point, enforce the persistent spin textures (PST) to occur in full BZ. We induce the Rashba splitting by breaking the $σ_h$ through an out-of-plane external electric field (EEF). The inversion asymmetric site point group of the W atom introduces the hidden spin polarization in centrosymmetric layered bulk counterparts. Therefore, the spin-layer locking effect, namely, energy degenerate opposite spins spatially segregated in the top and bottom W layers, has been identified. Our low energy $k.p$ model demonstrates that the PST along the M-K line is robust to EEF and layer thickness, making them suitable for applications in spintronics and valleytronics.

cond-mat.mtrl-sci↗

arXiv2022

Exploring strong and weak topological states on isostructural substitutions in TlBiSe2

Topological Insulators (TIs) are unique materials where insulating bulk hosts linearly dispersing surface states protected by the Time-Reversal Symmetry (TRS). These states lead to dissipationless current flow, which makes this class of materials highly promising for spintronic applications. Here, we predict new TIs via high-throughput screening by employing state-of-the-art first-principles based methodologies, viz., Density Functional Theory (DFT) and many-body perturbation theory (G0W0) combined with Spin-Orbit Coupling (SOC). For this, we take a well-known 3D TI, TlBiSe2 and perform complete substitution with suitable materials at different sites to check if the obtained isostructural materials exhibit topological properties. Subsequently, we scan these materials based on SOC-induced parity inversion at Time-Reversal Invariant Momenta (TRIM). Later, to confirm the topological nature of selected materials, we plot their surface states along with calculation of Z2 invariants. Our results show that GaBiSe2 is a Strong Topological Insulator (STI). Besides, we report six Weak Topological Insulators (WTIs) viz. PbBiSe2, SnBiSe2, SbBiSe2, Bi2Se2, TlSnSe2 and PbSbSe2. We have further verified that all the reported TIs are dynamically stable showing all real phonon modes of vibration.

cond-mat.mtrl-sci↗

arXiv2022

Chalcogenide Perovskites: An Emerging Class of Semiconductors for Optoelectronics

Chalcogenide perovskites have received considerable interest in photovoltaic research community owing to their stability (thermal and aqueous), non-toxicity and lead free composition. However, to date a theoretical study mainly focusing on the excitonic and polaronic properties are not explored rigorously, due to its huge computational demand. Herein, we capture the excitonic and polaronic effects in a series of chalcogenide perovskites ABS$_3$ where A=Ba, Ca, Sr, and B=Hf, Sn by employing state-of-the art hybrid density functional theory and many body perturbative approaches viz. GW and BSE. We find that these perovskites possess a large exciton binding energy than 3D inorganic-organic hybrid halide perovskites. We examine the interplay of electronic and ionic contribution to the dielectric screening, and conclude that electronic contribution is dominant over the ionic contribution. Further using Feynman polaron model, polaron parameters are computed, and we observe that charge separated polaronic states are less stable than bound excitons. Finally, the theoretically calculated spectroscopic limited maximum efficiency (SLME) suggests that among all chalcogenide perovskites, CaSnS$_3$ could serve as a best choice for photovoltaic applications.

cond-mat.mtrl-sci↗

arXiv2022

Sn/Ge substitution in ((C$_\textrm{n}$H$_{2\textrm{n}-1}$NH$_3$)$_2$PbI$_4$; n=3): An emerging 2D layered hybrid perovskites with enhanced optoelectronic properties$^†$

Two-dimensional (2D) perovskites show higher stability in comparison to their three-dimensional (3D) counterparts. Therefore, 2D perovskites have invoked remarkable attention in basic understanding of their physical properties and optoelectronic applications. Here we present a low-dimensional naturally self-assembled inorganic-organic (IO) hybrid systems based on primary cyclic ammonium-based (C$_{\textrm{n}}$H$_{2\textrm{n}-1}$NH$_{3}$) semiconductor series [viz. ((C$_{\textrm{n}}$H$_{2\textrm{n}-1}$ NH$_3$)$_2$PbI$_4$; n=3-6)]. However, the wide bandgap nature and presence of toxicity due to lead (Pb) prohibit their applications. Therefore, in the present work, we study the role of Ge/Sn substitution and Pb-vacancy (Pb-$\boxtimes$) to reduce concentration of Pb and to enhance solar cell efficiency by the formation of mixed perovskite structures. We have discussed the effect of spin-orbit coupling (SOC) using state-of-the-art hybrid density functional theory (DFT). We find the mixed conformers with Pb-$\boxtimes$ do not possess structural stability. Moreover, they have indirect bandgap, which is not good for solar cell applications. Only those conformers, which have favourable thermodynamics and structural stability, are considered for further study of optical properties. Our results infer that Sn substitution is more favorable than that of Ge in replacing Pb and enhancing the efficiency. Exciton binding energies calculated using Wannier-Mott approach for pristine and substituted conformers are larger than lead halide perovskites, while the electron-phonon coupling is smaller in the former. From computed spectroscopic limited maximum efficiency (SLME), these 2D perovskites show enough promise as alternatives to conventional lead halide perovskites.

cond-mat.mtrl-sci↗

arXiv2022

Full-plane persistent spin textures with cubic order intrinsic and anisotropic band splitting in bulk Lead-free materials

Spin-orbit coupling (SOC) effects occurring in noncentrosymmetric materials are known to be responsible for nontrivial spin configurations and a number of emergent physical phenomena such as electrical control of spin degrees of freedom and spin-to-charge conversion. The materials preserving a uniform spin configuration in the momentum-space, known as persistent spin texture (PST), provide long carrier spin lifetimes through persistent spin helix (PSH) mechanism. However, most of the PST studied till now are attributed to the linear in \textbf{\textit{k}} splitting and cease to exist locally around certain high-symmetry-point of first Brillouin Zone (FBZ). The persistent spin textures with purely cubic spin splittings have drawn attention owing to unique benefits in spin transport. Here, by using the relativistic first-principles calculations supplemented with \textbf{\textit{k.p}} analysis, we report the emergence of purely cubic splitting (PCS) belonging to $D_{3h}$ point group, which is enforced by in-plane mirror and three-fold rotation operations. In addition, the in-plane mirror symmetry operation sustains the PST in larger region (i.e. full planes) of FBZ alongside giant spin splitting. Our results also demonstrate how application of uniaxial strain could be envisaged to tune the magnitude of the PCS, preserving the PST. The observed PSTs provide a route to non-dephasing spin transport with larger spin-Hall conductivity, thus offering a promising platform for future spintronics devices.

cond-mat.mtrl-sci↗

arXiv2022

Metalated Porous-Organic-Polymer Renders Mustard-Gas Simulant Harmless: Core Planarity Matters

The presence of open active metal sites in Metal-Organic Frameworks (MOFs) exhibit higher catalytic activity. However, rational accomplishment of MOFs in heterogeneous catalysis is limited due to coordination bonds. Recently balanced characteristic feature with combination of both the covalent bonds (structural stability) and open metal sites (single site catalysis) introduced an entirely organic alternative architecture named as Metalated Porous-Organic-Polymers (M-POPs). In this contribution, we demonstrate successful construction of two Fe-POPs (Fe-Tt-POP & Fe-Rb-POP) by ternary copolymerization approach for catalytic oxidative decontamination of different sulfur-based mustard gas simulants. Fe-Tt-POP exhibited superior catalytic performance for oxidation of the thioanisole (TA) studied in terms of conversion (99% after 13 h) in comparison with Fe-Rb-POP (43% after 13h). The remarkable difference in the mechanistic pathways towards catalytic performance for oxidation of TA was investigated by in situ operando Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analysis, complemented by Density Functional Theory (DFT) computational study.

cond-mat.mtrl-sci↗

arXiv2021

Synergistic effect of workfunction and acoustic impedance mismatch for improved thermoelectric performance in GeTe/WC composite

The preparation of composite materials is promising for concurrent optimization of electrical and thermal transport properties to realize an improved thermoelectric (TE) performance. We report the effect of work function and acoustic impedance mismatch (AIM) on the TE properties of (1-z)Ge0.87Mn0.05Sb0.08Te/(z)WC composite. In particular, a composite consisting of Mn and Sb co-doped GeTe as a matrix and WC as a dispersed phase is prepared, and its structural and TE properties are investigated. The simultaneous increase in electrical conductivity (σ) and Seebeck coefficient (α) with WC volume fraction (z) results in an enhanced power factor (α^2σ) in the composite. The rise in σ is attributed to increased carrier mobility in the composite. This is further established from the work function measurement using the Kelvin probe force microscopy (KPFM) technique and is also supported by the density functional theory (DFT) calculations. The difference in elastic properties (sound velocity) between Ge0.87Mn0.05Sb0.08Te and WC results in a high AIM that leads to a large interface thermal resistance (Rint) between the phases. The correlation between Rint and the Kapitza radius results in reduced phonon thermal conductivity (κ_ph) of the composite and is discussed using the Bruggeman asymmetrical model. The decrease in κ_{ph} is further established using phonon dispersion calculations that indicates the decrease in phonon group velocity in the composite. The simultaneous effect of enhanced α^2σ and reduced κ_ph results in a maximum figure of merit (zT) of 1.93 at 773K for (1-z)Ge0.87Mn0.05Sb0.08Te/(z)WC composite having z=0.010. This study shows promise to achieve higher zTav across a wide range of composite materials having similar electronic structure and different elastic properties.

physics.app-ph↗

arXiv2021

Lead Free Alloyed Double Perovskites: An Emerging Class of Materials from Many-Body Perturbation Theory

The discovery of lead free all-inorganic alloyed double perovskites have revolutionized photovoltaic research, showing promising light emitting efficiency and its tunability. However, detailed studies regarding optical, exciton, polaron and transport properties remain unexplored. Here, we report a theoretical study on the variation of carrier-lattice interaction and optoelectronic properties of pristine as well as alloyed Cs$_2$AgInCl$_6$ double perovskites. We have employed many-body perturbation theory (G$_0$W$_0$@HSE06) and density functional perturbation theory (DFPT) to compute exciton binding energy (E$_\textrm{B}$) and exciton lifetime of different alloyed double perovskites. We find that phonon scattering limits charge-carrier mobilities and thus, plays an important role in the development of high-efficiency perovskite photovoltaics. In view of this, dominant carrier-phonon scattering is observed via Fröhlich mechanism near room temperature. Moreover, we observe a noticeable increase in hole and electron mobilities on alloying. We believe that our results will be helpful to gain a better understanding of the optoelectronic properties and lattice dynamics of these double perovskites.

cond-mat.mtrl-sci↗

arXiv2021

Origin of Rashba spin-splitting and strain tunability in ferroelectric bulk CsPbF$_3$

Spin-orbit coupling (SOC) in conjunction with broken inversion symmetry acts as a key ingredient for several intriguing quantum phenomena viz. persistent spin textures, topological surface states and Rashba-Dresselhaus (RD) effects. The coexistence of spontaneous polarization and the RD effect in ferroelectric materials enables the electrical control of spin degree of freedom. In light of this, we explore here the ferroelectric lead halide perovskite viz. CsPbF$_3$ as a potential candidate in the field of spintronics by employing state-of-the-art first-principles based methodologies viz. density functional theory (DFT) with semi-local and hybrid functional (HSE06) combined with spin-orbit coupling (SOC) and many-body perturbation theory (G$_0$W$_0$). For a deeper understanding of the observed spin-splitting, we have analyzed the spin textures within the combined framework of DFT and $\textbf{k.p}$ model Hamiltonian. The latter confirms that there is no out of plane spin component indicating that the Rashba splitting dominates over Dresselhaus splitting in this system. Owing to the presence of Pb-6$p$ orbital in conduction band, the large value of Rashba coefficient ($α_R$) at conduction band minimum (CBm) is noticed in comparison to that of at the valence band maximum (VBM). Notably, we also observe that strength of Rashba spin-splitting can be substancially tuned on application of uniaxial strain ($\pm5\%$). This finding will further pave the path for perovskite-based spintronics devices.

cond-mat.mtrl-sci↗

arXiv2021

Competition of Core-Shell and Janus Morphology in Alloy Nanoparticles: Insights From a Phase-Field Model

Bimetallic nanoparticles (BNPs) exhibit diverse morphologies such as core-shell, Janus, onion-like, quasi-Janus, and homogeneous structures. Although extensive effort has been directed towards understanding the equilibrium configurations of BNPs, kinetic mechanisms involved in their development have not been explored systematically. Since these systems often contain a miscibility gap, experimental studies have alluded to spinodal decomposition (SD) as a likely mechanism for the formation of such structures. We present a novel phase-field model for confined (embedded)systems to study SD-induced morphological evolution within a BNP. It initiates with the formation of compositionally modulated rings as a result of surface-directed SD and eventually develops into core-shell or Janus structures due to coarsening/breakdown of the rings. The final configuration depends crucially on contact angle and particle size -Janus is favored at smaller sizes and higher contact angles. Our simulations also illustrate the formation of metastable, kinetically trapped structures as a result of competition between capillarity and diffusion.

cond-mat.mtrl-sci↗