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| 2. |
- Banerjee, Hrishit, et al.
(författare)
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Cationic Effect on Pressure Driven Spin-State Transition and Cooperativity in Hybrid Perovskites
- 2016
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 28:22, s. 8379-8384
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid or metal organic framework (MOP) perovskites of general composition, ABX(3), are known to show interesting properties that can lead to a variety of technological applications. Our first-principles study shows they are also potential candidates for exhibiting cooperative spin-state transitions upon application of external stimuli. We demonstrate this by considering two specific Fe-based MOF perovskites, namely dimethylammonium iron formate, [CH3NH2CH3][Fe(HCOO)(3)], and hydroxylammonium iron formate, [NH3OH][Fe(HCOO)(3)]. Both the compounds are found to undergo high-spin (S = 2) to low-spin (S = 0) transition at Fe(II) site upon application of moderate strength of hydrostatic pressure, along with large hysteresis. This spin-state transition is signaled by the changes in electronic, magnetic, and optical properties. We find both the transition pressure and the width of the hysteresis to be strongly dependent on the choice of A-site cation, dimethylammonium or hydroxylammonium, implying that tuning of spin-switching properties is achievable by chemical variation of the amine cation in the structure. Our findings open up novel functionalities in this family of materials of recent interest, which can have important usage in sensors and memory devices.
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| 3. |
- Banerjee, Hrishit, et al.
(författare)
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Design and Control of Cooperativity in Spin-Crossover in Metal-Organic Complexes : A Theoretical Overview
- 2017
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Ingår i: INORGANICS. - : MDPI AG. - 2304-6740. ; 5:3
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Forskningsöversikt (refereegranskat)abstract
- Metal organic complexes consisting of transition metal centers linked by organic ligands, may show bistability which enables the system to be observed in two different electronic states depending on external condition. One of the spectacular examples of molecular bistability is the spin-crossover phenomena. Spin-Crossover (SCO) describes the phenomena in which the transition metal ion in the complex under the influence of external stimuli may show a crossover between a low-spin and high-spin state. For applications in memory devices, it is desirable to make the SCO phenomena cooperative, which may happen with associated hysteresis effect. In this respect, compounds with extended solid state structures containing metal ions connected by organic spacer linkers like linear polymers, coordination network solids are preferred candidates over isolated molecules or molecular assemblies. The microscopic understanding, design and control of mechanism driving cooperativity, however, are challenging. In this review we discuss the recent theoretical progress in this direction.
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| 4. |
- Chowdhury, Suman, et al.
(författare)
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A real-space study of random extended defects in solids : Application to disordered Stone–Wales defects in graphene
- 2014
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier BV. - 1386-9477 .- 1873-1759. ; 61:0, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- Abstract We propose here a first-principles, parameter free, real space method for the study of disordered extended defects in solids. We shall illustrate the power of the technique with an application to graphene sheets with randomly placed Stone–Wales defects and shall examine the signature of such random defects on the density of states as a function of their concentration. The technique is general enough to be applied to a whole class of systems with lattice translational symmetry broken not only locally but by extended defects and defect clusters. The real space approach will allow us to distinguish signatures of specific defects and defect clusters.
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| 5. |
- Jana, Somnath, et al.
(författare)
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Signature of an antiferromagnetic metallic ground state in heavily electron-doped Sr2FeMoO6
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:5, s. 054433-
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Tidskriftsartikel (refereegranskat)abstract
- Sr2FeMoO6 is a well-known double perovskite with exciting high-temperature magnetic properties. Through various magnetic and spectroscopic measurements, we collect compelling evidence here that this compound can be driven into a rare three-dimensional antiferromagnetic metallic state by heavy electron doping (70% Sr2+ substitution by La3+). Moreover, local structural study of these Sr2-xLaxFeMoO6 (1.0 <= x <= 1.5) compounds reveals unusual atomic scale phase distribution in terms of La,Fe- and Sr,Mo-rich regions driven by strong La-O covalency, a phenomenon hitherto undisclosed in double perovskites. The general trend of our findings is in agreement with theoretical calculations carried out on realistic structures having local chemical fluctuations, which reconfirms the relevance of the kinetic-energy-driven magnetic model.
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| 6. |
- Maldonado, Pablo, et al.
(författare)
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Two-step spin-switchable tetranuclear Fe(II) molecular solid : Ab initio theory and predictions
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:2, s. 020408-
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Tidskriftsartikel (refereegranskat)abstract
- Using density functional theory supplemented with on-site Coulomb U interaction in combination with ab initio molecular dynamics simulations, we investigate the spin-crossover (SCO) properties of a Fe(II) based cyanide-bridged square molecular system, [Fe-4(II)(mu-CN)(4)(bpy)(4)(tpa)(2)](PF6)(4) (where bpy = 2,2'-bipyridine and tpa = tris(2-pyridylmethyl) amine], exhibiting a two-step SCO transition. The ab initio calculated SCO temperatures are found to show remarkably good agreement with experimentally measured spin conversion temperatures [M. Nihei et al., Angew. Chem., Int. Ed. 44, 6484 (2005)]. Our theoretical study predicts further chemo switching of the spin state by introduction of guest molecules such as CO2, CS2, and H2O into the porous topology of the system, which would add another dimensionality to this interesting material.
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| 7. |
- Roondhe, Basant, et al.
(författare)
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Enhancing the electronic and phonon transport properties of two-dimensional hexagonal boron nitride through oxygenation : A first principles study
- 2020
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 533
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Tidskriftsartikel (refereegranskat)abstract
- Thermoelectric (TE) materials have gathered much attention due to their ability to harvest waste heat energy. To fulfill the goal of sufficient efficiency conversion two important parameters are required (1) low thermal conductivity and (2) high power factor (PF). Two dimensional (2D) hexagonal boron nitride (h-BN) is isostructural with graphene and composed of excellent opto-electronic properties, high mechanical and chemical stability, further exhibiting wide range of applications in diverse areas. Insulating nature of 2D h-BN can be tuned by different approaches such as functionalization, doping or hybrid structures. Therefore, present work focuses on the oxygenation of h-BN, i.e. BNO, for optimization of electronic and phonon transport properties using the state-of-the-art density functional theory (DFT) and Boltzmann transport equation. The presence of oxygen in out-of-plane direction leads to the buckling in h-BN resulting in 65% decrement in the lattice thermal conductivity of BNO (103.66 W/mK) at room temperature. Further, the giant reduction (from 4.63 to 0.7 eV) in electronic bandgap after oxygenation in h-BN is found, leading to the nine times larger electrical conductivity as compared to h-BN. The calculated power factor is almost double in case of BNO. Present study suggests, BNO might have promising utilization in high temperature thermoelectric applications.
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| 8. |
- Saha-Dasgupta, Tanusri, et al.
(författare)
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Computational design of magnetic metal-organic complexes and coordination polymers with spin-switchable functionalities
- 2014
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Ingår i: MRS bulletin. - : Springer Science and Business Media LLC. - 0883-7694 .- 1938-1425. ; 39:7, s. 614-620
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic metal-organic complexes and coordination polymer frameworks can exhibit a transition between two different spin states of the integrated transition-metal ion, an attribute known as a spin-crossover (SCO) transition. This is a spectacular phenomenon that provides magnetic bi-stability and reversible spin-switchability to the material. Consequently, the magnetic state of the metal-organic center can be externally steered by temperature, pressure, or light irradiation. SCO molecules therefore are promising materials for various technological applications, such as spintronics devices, photo-switches, color displays, and information storage units. In spite of the importance of SCO materials in spintronics and other applications, the materials-specifi c understanding of the SCO phenomenon has remained a challenge. Here we survey recent developments in first-principles computational design of SCO metal-organic materials. A major outcome of recent state-of-the-art investigations is that an accurate quantitative description and even computational design of SCO materials can be provided by density functional theory-based electronic structure calculations combined with ab initio molecular dynamics simulations.
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| 9. |
- Sarkar, Soumyajit, et al.
(författare)
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Spin-crossover in cyanide-based bimetallic coordination polymers : insight from first-principles calculations
- 2011
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 21:36, s. 13832-13840
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Tidskriftsartikel (refereegranskat)abstract
- Employing density functional theory (DFT) based calculations, we perform a computational investigation to unravel the intricate spin-crossover transitions that have been observed (Niel et al., Angew. Chem., Int. Ed., 2003, 42, 3760) in cyanide-based bimetallic coordination polymers, [Fe(pmd)-(H(2)O){M(CN)(2)}(2)]center dot H(2)O (M = Ag or Au and pmd pyrimidine). Our calculations provide an explanation for the observed temperature-induced low-spin (LS) to high-spin (HS) spin-crossover occurring in both Ag and Au hydrated networks due to Fe-N bond stretching, concomitant with charge re-distribution from Fe to the ligands. For dehydrated compounds, we find that relativistic effects in Au versus Ag lead to differences in the degree of covalent bonding, which in turn, gives rise to a differential behavior, viz. the Ag dehydrated network exhibits a LS-HS spin transition whereas the Au hydrated network remains in HS state. As a critical test of our first-principles study we propose to investigate a Cu-based bimetallic coordination polymer, which we predict to be in LS state.
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