| 1. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Thermodynamic properties for metal oxides from first-principles
- 2024
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Ingår i: Computational Materials Science. - 0927-0256. ; 233
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Tidskriftsartikel (refereegranskat)abstract
- In this study, an efficient first-principles approach for calculating the thermodynamic properties of mixed metal oxides at high temperatures is demonstrated. More precisely, this procedure combines density functional theory and harmonic phonon calculations with tabulated thermochemical data to predict the heat capacity, formation energy, and entropy of important metal oxides. Alloy cluster expansions are, moreover, employed to represent phases that display chemical ordering as well as to calculate the configurational contribution to the specific heat capacity. The methodology can, therefore, be applied to compounds with vacancies and variable site occupancies. Results are, moreover, presented for a number of systems of high practical relevance: Fe–K–Ti–O, K–Mn–O, and Ca–Mn–O. For the reference materials, the agreement with experimental measurements is exceptional in the case of ilmenite (FeTiO3) and good for CaMnO3. When the generated data is used in multi-phase thermodynamic calculations to represent materials for which experimental data is not available, the predicted phase-diagrams for the K–Mn–O and K–Ti–O systems change dramatically. The demonstrated methodology is highly useful for obtaining approximate values on key thermodynamic properties in cases where experimental data is hard to obtain, inaccurate or missing.
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| 2. |
- Löfgren, Joakim, 1989, et al.
(författare)
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Computational assessment of the efficacy of halides as shape-directing agents in nanoparticle growth
- 2020
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Ingår i: Physical Review Materials. - 2475-9953. ; 4:9
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Tidskriftsartikel (refereegranskat)abstract
- We report a comprehensive study of aqueous halide adsorption on nanoparticles of gold and palladium that addresses several limitations hampering the use of atomistic modeling as a tool for understanding and improving wet-chemical synthesis and related applications. A combination of thermodynamic modeling with density functional theory (DFT) calculations and experimental data is used to predict equilibrium shapes of halide-covered nanoparticles as a function of the chemical environment. To ensure realistic and experimentally relevant results, we account for solvent effects and include a large set of vicinal surfaces, several adsorbate coverages, as well as decahedral particles. While the observed stabilization is not significant enough to result in thermodynamic stability of anisotropic shapes such as nanocubes, nonuniformity in the halide coverage indicates the possibility of obtaining such shapes as kinetic products. With regard to technical challenges, we show that inclusion of surface-solvent interactions leads to qualitative changes in the predicted shape. Furthermore, accounting for nonlocal interactions on the functional level yields a more accurate description of surface systems.
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| 3. |
- Adanez-Rubio, Inaki, et al.
(författare)
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Use of a high-entropy oxide as an oxygen carrier for chemical looping
- 2024
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Ingår i: Energy. - 0360-5442. ; 298
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Tidskriftsartikel (refereegranskat)abstract
- One mixed oxide with 5 cations in equimolar proportions in the sublattice, to fulfil high-entropy oxide (HEO) criteria, has been developed and investigated as oxygen carrier for chemical looping combustion processes. As far as we know, nobody has explored this class of material for chemical looping combustion. Material is prepared by direct mixing of five metal oxides (CuO, Mn2O3, Fe2O3, TiO2, MgO), followed by calcination at 1000, 1100 and 1200 °C for 6 h in air. XRD characterization provides strong evidence that the synthesized oxygen carriers possess the hallmark properties of HEO, and SEM-EDX analysis shows an overall homogeneous metal distribution. Materials have one main cubic phase with the empirical formula MnCuMgFeTiO7, dominating under all conditions. One of the key objectives of this study is achieved, reduce chemical stress during redox cycles. Oxygen transfer capability is investigated by thermogravimetric analysis and batch fluidized bed reactor experiments for different fuels and atmospheres. Mass-based oxygen transport capacities for lattice oxygen and oxygen uncoupling are around 5.5 wt% and 1.1 wt%, respectively. This work opens up a new dimension for the future preparation of oxygen carriers for chemical looping processes, since the vast compositional space of HEO provides opportunities to tune both chemical and physical characteristics.
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| 4. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Discovery of Oxygen Carriers by Mining a First-Principle Database
- 2023
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Ingår i: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 127:20, s. 9437-9451
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping is an innovative technique that relies, to a large extent, on the possibility of finding new oxygen carriers. Until now, these materials have primarily been identified via experimental techniques and therefrom derived insights. However, this is both costly and time-consuming. To speed-up this process, we have applied a computational screening approach based on energetic data retrieved from the Open Quantum Materials Database. In particular, we have considered combinations of all mono-, bi-, and trimetallic alloys and mixed oxides with up to three distinctive phases. Here, we specifically focus on a technique referred to as chemical looping oxygen uncoupling, which is especially suitable for solid fuels, e.g., combustion of biomass for negative CO2 emissions. The formation energies obtained for the materials of interest were used to identify phase transitions that are likely to occur under conditions relevant for chemical looping oxygen uncoupling. Given these criteria, the initial list of 300000 materials is reduced by a factor of 20, and after filtering out rare, radioactive, toxic, or harmful elements only 1000 remain. When considering the abundance of elements in the ranking criteria, most of the highest ranking phases include Cu, Mn, and Fe. This adds credibility to the procedure, as many viable oxygen carriers for chemical looping oxygen uncoupling that have been studied experimentally contain these elements. While Cr-based materials have not been widely explored for this application, our study suggests that this might be worthwhile since these occur more frequently than Fe. Other elements that would be interesting as additional components include Ba, K, Na, Al, and Si.
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| 5. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Efficient Calculation of the Lattice Thermal Conductivity by Atomistic Simulations with Ab Initio Accuracy
- 2022
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Ingår i: Advanced Theory and Simulations. - : Wiley. - 2513-0390. ; 5:2
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Tidskriftsartikel (refereegranskat)abstract
- High-order force constant expansions can provide accurate representations of the potential energy surface relevant to vibrational motion. They can be efficiently parametrized using quantum mechanical calculations and subsequently sampled at a fraction of the cost of the underlying reference calculations. Here, force constant expansions are combined via the hiphive package with GPU-accelerated molecular dynamics simulations via the GPUMD package to obtain an accurate, transferable, and efficient approach for sampling the dynamical properties of materials. The performance of this methodology is demonstrated by applying it both to materials with very low thermal conductivity (Ba8Ga16Ge30, SnSe) and a material with a relatively high lattice thermal conductivity (monolayer-MoS2). These cases cover both situations with weak (monolayer-MoS2, SnSe) and strong (Ba8Ga16Ge30) pho renormalization. The simulations also enable to access complementary information such as the spectral thermal conductivity, which allows to discriminate the contribution by different phonon modes while accounting for scattering to all orders. The software packages described here are made available to the scientific community as free and open-source software in order to encourage the more widespread use of these techniques as well as their evolution through continuous and collaborative development.
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| 6. |
- Brorsson, Joakim, 1988, et al.
(författare)
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First-Principles Study of Order-Disorder Transitions in Pseudobinary Clathrates
- 2021
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:41, s. 22817-22826
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Tidskriftsartikel (refereegranskat)abstract
- It has been recently demonstrated that the pseudoternary Ba8AlxGayGe46-x-y clathrate undergoes an order-disorder transition with increasing temperature that can be observed via site occupation factors (SOFs) and manifests itself, e.g., in electrical transport properties. Here, we generalize this result and analyze the characteristics of this order-disorder transition in the pseudobinary clathrates Ba8GaxGe46-x, Ba8GaxSi46-x, Ba8AlxGe46-x, and Ba8AlxSi46-x. To this end, we employ atomistic simulations that combine alloy cluster expansions trained against density functional theory calculations with Wang-Landau and ensemble Monte Carlo simulations. The simulations show that all four systems studied here display order-disorder transitions for at least some composition range. Based on an extensive literature survey, we also provide evidence for signatures of the transition in earlier experimental studies that to the best of our knowledge have hitherto not been related to such transitions. The predicted transition temperatures are lower for Ba8GaxGe46-x and Ba8GaxSi46-x than for Ba8AlxGe46-x and Ba8AlxSi46-x, although it appears that the simulations underestimate the transition temperatures for Ga-containing systems compared to the experiment. This nonetheless provides a sensible explanation for why the experimentally determined Al SOFs agree better with the simulated higherature disordered configurations, while the Ga SOFs more closely agree with the simulated ground-state configurations. As a result of stronger interactions, the SOFs vary substantially, especially near the stoichiometric 16:30 composition, providing an indication of why it has proved difficult to synthesize Ba8AlxGe46-x and Ba8AlxSi46-x samples at this ratio. The present study thereby yields detailed atomic-scale insights into the ordering in inorganic clathrates that, given the connection to transport properties established earlier, are not only useful from a fundamental perspective but also relevant for applications.
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| 7. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Order-Disorder Transition in Inorganic Clathrates Controls Electrical Transport Properties
- 2021
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 33:12, s. 4500-4509
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Tidskriftsartikel (refereegranskat)abstract
- Inorganic clathrates have been extensively investigated owing to their unique and intriguing atomic structure as well as their potential as thermoelectric materials. The connection between the chemical ordering and the physical properties has, however, remained elusive. Here, this relation is uncovered through a combination of first-principles calculations, atomistic simulations, and experimental measurements of thermodynamic as well as electrical transport properties. This approach is, specifically, used to reveal the existence of an order-disorder transition in the quaternary clathrate series Ba8AlxGa16-xGe30. The results, furthermore, demonstrate that this phenomenon is responsible for the discontinuity in the heat capacity that has been observed previously. Moreover, the unusual temperature dependence of both Seebeck coefficient and electrical conductivity can be fully explained by the alterations of the band structure brought about by the phase transformation. It is finally argued that the phenomenology described here is not limited to this particular material but should be present in a wide range of inorganic clathrates and could even be observed in other materials that exhibit chemical ordering on at least one sublattice.
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| 8. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Strategic Optimization of the Electronic Transport Properties of Pseudo-Ternary Clathrates
- 2022
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Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X .- 2199-160X. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- While alloying is a powerful handle for materials engineering, it is an ongoing challenge to navigate the large and complex parameter space of these materials. This applies in particular for thermoelectrics and even more so clathrates. Here, a combination of density functional theory calculations, alloy cluster expansions, Monte Carlo simulations, and Boltzmann transport theory calculations is used to identify compositions that yield high power factors in the pseudo-ternary clathrates Ba8AlxGayGe46−x−y and Ba8GaxGeySi46−x−y, while accounting for weight and raw material costs. The results show how a cost-efficient performance can be achieved by reducing the number of Al and Ga atoms per unit cell, while compensating the resulting increase in the carrier concentration via an extrinsic dopant. The approach used in this study is transferable and can be a useful tool for mapping the thermodynamic and transport properties of other multinary systems.
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| 9. |
- Brorsson, Joakim, 1988
(författare)
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Unlocking the potential of a caged star: Thermoelectric quaternary clathrates
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heat losses are an inevitable consequence of any energy conversion process, dictated by the second law of thermodynamics. This not only leads to an eternal struggle, via the pursuit of maximal efficiency, it also undermines our efforts to solve the two issues that pose the most significant challenges to modern society: climate change and the worlds surging energy need. Thanks to our inherent ingenuity, humankind has, however, been adept at finding ways of harnessing the power of heat; from the fires that lit up the neolithic era to the steam engines of the industrial revolution. Thermoelectrics can, in some sense, be seen as the next step in this endeavour, since they allow the direct conversion of a temperature difference to an electric voltage. This thesis summarises a seven year long journey, which has focused on a fascinating and unique group of thermoelectric materials, namely inorganic clathrates. Though these have been the subject of intense research over the last three decades, many of their properties and attributes have, as of yet, not been fully explored. In particular, this project has addressed three fundamental questions: (i) Why is the lattice thermal conductivity intrinsically low? (ii) What is the impact of chemical ordering on the physical properties? (iii) How can the electronic transport be optimised? Due to the inherent complexity of these materials, computational and experimental methods should ideally be used in tandem, in order to gain further insights. This project has, thus, involved the use of both atomic scale simulations, based on a combination of density functional theory, alloy cluster expansions, and Monte Carlo simulations, as well as advanced measurement and characterisation techniques. Through these efforts, the confusion regarding the origin of the low lattice thermal conductivity has partly been clarified. In addition, it has been shown that chemical ordering in these materials leads to the emergence of an order-disorder transition, which has a direct impact on the physical properties. Last but not least, it is found that the consideration of ternary systems can facilitate the enhancement of the thermoelectric performance by enabling not only independent tuning of doping level and band structure via the composition, but also manipulation of the nano- and microstructure.
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| 10. |
- Lindroth, Daniel, 1978, et al.
(författare)
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Thermal conductivity in intermetallic clathrates: A first-principles perspective
- 2019
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 100:4
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Tidskriftsartikel (refereegranskat)abstract
- Inorganic clathrates such as Ba8GaxGe46-x and Ba8AlxSi46-x commonly exhibit very low thermal conductivities. A quantitative computational description of this important property has proven difficult, in part due to the large unit cell, the role of disorder, and the fact that both electronic carriers and phonons contribute to transport. Here, we conduct a systematic analysis of the temperature and composition dependence of low-frequency modes associated with guest species in Ba8GaxGe46-x and Ba8AlxSi46-x ("rattler modes"), as well as thermal transport in stoichiometric Ba8Ga16Ge30. To this end, we account for phonon-phonon interactions by means of temperature-dependent effective interatomic force constants, which we find to be crucial in order to achieve an accurate description of the lattice part of the thermal conductivity. While the analysis of the thermal conductivity is often largely focused on the rattler modes, here it is shown that at room temperatures modes with ω 10meV account for 50% of lattice heat transport. Finally, the electronic contribution to the thermal conductivity is computed, which shows the Wiedemann-Franz law to be only approximately fulfilled. As a result, it is crucial to employ the correct prefactor when separating electronic and lattice contributions for experimental data.
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