The impact of tilt grain boundaries on the thermal transport in perovskite SrTiO3 layered nanostructures. A computational study

Stacking of interfaces at different length-scales affect the lattice thermal conductivity of strontium titanate layered nanostructures improving their thermoelectric performance

Enhanced Li-ion dynamics in trivalently doped Lithium Phosphidosilicate Li2SiP2: A candidate material as a solid li electrolyte

Oxide and sulphide solid electrolyte materials have enjoyed significant interest in the solid-state battery community. Phosphide materials however are relatively unexplored despite the potential for being high lithium containing systems. This work reports on the phosphidosilicate system Li2SiP2 , one of many systems in the Li-Si-P phase diagram. The phosphidosilicates display complex structures and very large unit cells, which present challenges for ab-initio simulations. We present the first computational report on the theoretical ionic conductivity and related diffusion mechanisms of the material Li2SiP2 , selected due to it’s unusual supertetrahedral framework which is a recurrent motif amongst the phosphidosilicates. Group 13 dopants have also been introduced into Li2SiP2 showing preference for the silicon site over the lithium site, with Al0 Si doping showing extremely low defect incorporation energies of 0.05 eV, with no increase in defect energy up to concentrations of 10% Al0 Si. Furthermore, clustering of Al0 Si has been found to be unfavourable, in line with trends seen in oxide zeolite structures. Ab-initio molecular dynamics (AIMD) simulations indicate high ionic conductivity in pure Li2SiP2 of up to 3.19 × 10−1 S.cm-1 at 700 K. Doping with 10% Al0 Si and associated Li• i compensating defects leads to higher ionic conductivities at lower temperatures when compared to pure Li2SiP2 . The activation energies to lithium diffusion were found to be low at 0.30 eV and 0.24 eV for pure and 10% Al0 Si doped Li2SiP2 respectively, in line with previous experimental observations of pure Li2SiP2 . Multiple lithium migration pathways have also been extracted, with some mechanisms displaying activation energies as low as 0.05 eV. Furthermore, our calculated intercalation voltages suggest that these materials are stable against lithium metal and therefore could be very attractive in stabilising the electrode/electrolyte interface

Atomistic modelling for the construction industry

Advances in computing power now make atomistic modelling a viable approach for the study of complex chemical processes in a number of applications including construction. We aim to apply these methods to processes such as the carbonation of lime mortars. The current research highlights the potential for studying construction materials using atomistic modelling. Computational models of different oxide structures simulating products of the thermal decomposition of dolomite support the view of some authors that suggest formation of phase separated calcium and magnesium minerals

Structure and lithium-ion dynamics in fluoride-doped cubic Li7La3Zr2O12 (LLZO) garnet for Li solid-state battery applications

The lithium-stuffed garnet Li7La3Zr2O12 (LLZO), when suitably doped, is a promising candidate material for use as a solid-state electrolyte within advanced Li-ion batteries. It possesses the thermal and mechanical stability of many inorganic ceramics, while exhibiting high Li+ ionic conductivities often associated with conventional liquid electrolytes, making it an ideal component for large-scale energy storage. However, only the high-temperature cubic phase has any meaningful Li-ion conductivity. Typically the formation of this phase is achieved through cation doping (e.g., Al3+ on the Li site) to lower the Li content and so disrupt Li ordering. However, Li-site doping, in particular, may potentially lead to some disruption of the Li-ion conduction pathways and suboptimal ionic conductivities. Consequently, other novel doping strategies involving the anion site are gaining traction, for example, F– for O2– as an alternative strategy to lower the Li content without directly blocking the lithium-diffusion pathways. For the first time, classical potential-based simulations have been employed to simulate the incorporation of fluoride anions into LLZO. Low incorporation energies have been calculated, suggesting fluoride anions are stable on the oxygen sites with a compensating lithium-ion vacancy defect. Molecular dynamics calculations suggest a definitive phase transition to the more desirable cubic phase of LLZO when doped with fluoride at temperature significantly lower than that for the tetragonal–cubic phase transition found for pure LLZO. Remarkably, the lithium-ion transport properties are shown to improve in the fluoride-doped samples particularly at low temperatures due to the stabilization of the cubic phase, suggesting anion doping of garnet systems may be a compelling alternative route to optimize the ionic conductivity

Atomistic insights of multiple stacking faults in CdTe thin-film photovoltaics: A DFT study

Stacking faults in CdTe were studied using DFT simulations. Twin and tetrahedral stacking fault energies are significantly lower than previously suggested, strongly correlating with their high density observed experimentally. No long range ordering was found for tetrahedral stacking faults while a resistance for polytype clustering was calculated. All experimentally observed faults were shown to be electronically benign when considered in isolation but increased density may produce shallow electron trap states

Concurrent La and A-site Vacancy Doping Modulates the Thermoelectric Response of SrTiO3. Experimental and Computational Evidence

To help understand the factors controlling the performance of one of the most promising n-type oxide thermoelectric SrTiO3, we need to explore structural control at the atomic level. In Sr1–xLa2x/3TiO3 ceramics (0.0 ≤ x ≤ 0.9), we determined that the thermal conductivity can be reduced and controlled through an interplay of La-substitution and A-site vacancies and the formation of a layered structure. The decrease in thermal conductivity with La and A-site vacancy substitution dominates the trend in the overall thermoelectric response. The maximum dimensionless figure of merit is 0.27 at 1070 K for composition x = 0.50 where half of the A-sites are occupied with La and vacancies. Atomic resolution Z-contrast imaging and atomic scale chemical analysis show that as the La content increases, A-site vacancies initially distribute randomly (x < 0.3), then cluster (x ≈ 0.5), and finally form layers (x = 0.9). The layering is accompanied by a structural phase transformation from cubic to orthorhombic and the formation of 90° rotational twins and antiphase boundaries, leading to the formation of localized supercells. The distribution of La and A-site vacancies contributes to a nonuniform distribution of atomic scale features. This combination induces temperature stable behavior in the material and reduces thermal conductivity, an important route to enhancement of the thermoelectric performance. A computational study confirmed that the thermal conductivity of SrTiO3 is lowered by the introduction of La and A-site vacancies as shown by the experiments. The modeling supports that a critical mass of A-site vacancies is needed to reduce thermal conductivity and that the arrangement of La, Sr, and A-site vacancies has a significant impact on thermal conductivity only at high La concentration

Ba6−3x Nd8+2x Ti18O54 Tungsten Bronze: A New High-Temperature n-Type Oxide Thermoelectric

Semiconducting Ba6−3x Nd8+2x Ti18O54 ceramics (with x = 0.00 to 0.85) were synthesized by the mixed oxide route followed by annealing in a reducing atmosphere; their high-temperature thermoelectric properties have been investigated. In conjunction with the experimental observations, atomistic simulations have been performed to investigate the anisotropic behavior of the lattice thermal conductivity. The ceramics show promising n-type thermoelectric properties with relatively high Seebeck coefficient, moderate electrical conductivity, and temperature-stable, low thermal conductivity; For example, the composition with x = 0.27 (i.e., Ba5.19Nd8.54Ti18O54) exhibited a Seebeck coefficient of S 1000K = 210 µV/K, electrical conductivity of σ 1000K = 60 S/cm, and thermal conductivity of k 1000K = 1.45 W/(m K), leading to a ZT value of 0.16 at 1000 K

The impact of tilt grain boundaries on the thermal transport in perovskite SrTiO₃ layered nanostructures. A computational study

This is an Open Access Article. It is published by Royal Society of Chemistry under the Creative Commons Attribution 3.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/3.0/Stacking of interfaces at different length-scales affect the lattice thermal conductivity of strontium titanate layered nanostructures improving their thermoelectric performance

Data for "The Impact of Tilt Grain Boundaries on the Thermal Transport in Perovskite SrTiO3 Layered Nanostructures. A Computational Study"

Datasets for computer simulations of tilt grain boundaries in SrTiO3, used for lattice dynamics and molecular dynamics calculations. These calculations were used in the paper, "The Impact of Tilt Grain Boundaries on the Thermal Transport in Perovskite SrTiO3 Layered Nanostructures: A Computational Study," to demonstrate how nanoscale structural features may be identified that can facilitate thermal transport in technologically important nanostructured materials such as SrTiO3.Details of the methodology may be found in the 'Computational methods' section of the associated paper, and in the readme.txt files included in the dataset.The following software was used in processing the data: LAMPPS (https://lammps.sandia.gov/); PHONOPY (https://atztogo.github.io/phonopy/); METADISE (https://doi.org/10.1039/FT9969200433).The phonopy directory contains the three structures to run through the simulation code: PHONOPY was used for the lattice dynamics calculations. The thermal_conductivity directory contains a series of folders giving the data for the molecular dynamics calculations using LAMMPS