Glassy, glass–ceramic, and crystalline lithium thiophosphates have attracted interest in their use as solid electrolytes in all-solid-state batteries. Despite similar structural motifs, including ...PS43–, P2S64–, and P2S74– polyhedra, these materials exhibit a wide range of possible compositions, crystal structures, and ionic conductivities. Here, we present a combined approach of Bragg diffraction, pair distribution function analysis, Raman spectroscopy, and 31P magic angle spinning nuclear magnetic resonance spectroscopy to study the underlying crystal structure of Li4P2S6. In this work, we show that the material crystallizes in a planar structural arrangement as a glass ceramic composite, explaining the observed relatively low ionic conductivity, depending on the fraction of glass content. Calculations based on density functional theory provide an understanding of occurring diffusion pathways and ionic conductivity of this Li+ ionic conductor.
The superionic conductor Cu2−δSe has been shown to be a promising thermoelectric at higher temperatures because of very low lattice thermal conductivities, attributed to the liquid-like mobility of ...copper ions in the superionic phase. In this work, we present the potential of copper selenide to achieve a high figure of merit at room temperature, if the intrinsically high hole carrier concentration can be reduced. Using bromine as a dopant, we show that reducing the charge carrier concentration in Cu2−δSe is in fact possible. Furthermore, we provide profound insight into the complex defect chemistry of bromine doped Cu2−δSe via various analytical methods and investigate the consequential influences on the thermoelectric transport properties. Here, we show, for the first time, the effect of copper vacancy formation as compensating defects when moving the Fermi level closer to the valence band edge. These compensating defects provide an explanation for the often seen doping inefficiencies in thermoelectrics via defect chemistry and guide further progress in the development of new thermoelectric materials.
C-S-H seeding in Portland cements is well known from basic scientific works and field applications. Moreover, this activation approach could be beneficial for low-CO2 cements under development where ...a general drawback is poor mechanical strengths during the first week of hydration. However, a mechanistic understanding of the different processes taking place when seeding is still not developed. Here, we contribute to this knowledge gap by studying one commercial Portland cement and two industrial-trial belite cements. Three different admixtures are employed, viz. two types of commercial C-S-H seeding and triisopropanolamine as a typical alkanolamine. A multitechnique approach is employed including calorimetry, ultrasonic pulse velocity, thermal analysis and Rietveld analysis of laboratory X-ray powder diffraction data. Chiefly, an in situ X-ray synchrotron diffraction study has allowed mapping out the evolution of every crystalline phase. Furthermore, the use of an internal standard permitted to measure the changes in the overall amorphous content. In a nutshell, alite and belite (phases) hydrations are not significantly accelerated by C-S-H seeding for the three studied cements. Conversely, sulphate and aluminate phase dissolutions are enhanced. Faster ettringite crystallisation contributes to the observed improved mechanical properties at early ages. Moreover, a synergistic effect between C-S-H seeding and alkanolamine addition is proved. The importance of these findings for the possible acceleration of low-CO2 cement hydration is discussed.
Calcined clays have received significant attention as a primary supplementary cementitious material (SCM) for reducing the CO2 footprint of cement, especially when combined with limestone in ...limestone calcined clay cement (LC3). However, it is widely recognized that the use of calcined clays leads to increased water and admixture demand, posing challenges in terms of slump-retention and rheology when using conventional admixtures developed for OPC. Superplasticizer demand is commonly correlated with the kaolin content of the raw clays. In this paper, we investigate and demonstrate the strong influence of the specific surface area of calcined clays on superplasticizers dosage by studying four different LC3 compositions ranging from 65% to 35% clinker content, using five calcined clays and two superplasticizers.
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•4 different LC3 systems ranging from 65% to 35% clinker content, using 5calcined clays and two superplasticizers.•The BET of the calcined clay and the amount of calcined clay in the cement composition govern the superplasticizer demand.•The iron content seems to be another influencing parameter on the admixture performance.•High-performing slump retainers are needed to obtain long open time with calcined clay cements.
Engineering of nanoscale structures is a requisite for controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require a conflicting combination ...of low thermal conductivity and low electrical resistivity. We report the thermoelectric properties of spark plasma sintered Magnéli phases WO
2.90
and WO
2.722
. The crystallographic shear planes, which are a typical feature of the crystal structures of Magnéli-type metal oxides, lead to a remarkably low thermal conductivity for WO
2.90
. The figures of merit (ZT = 0.13 at 1100 K for WO
2.90
and 0.07 at 1100 K for WO
2.722
) are relatively high for tungsten-oxygen compounds and metal oxides in general. The electrical resistivity of WO
2.722
shows a metallic behaviour with temperature, while WO
2.90
has the characteristics of a heavily doped semiconductor. The low thermopower of 80 μV K
−1
at 1100 K for WO
2.90
is attributed to its high charge carrier concentration. The enhanced thermoelectric performance for WO
2.90
compared to WO
2.722
originates from its much lower thermal conductivity, due to the presence of crystallographic shear and dislocations in the crystal structure. Our study is a proof of principle for the development of efficient and low-cost thermoelectric materials based on the use of intrinsically nanostructured materials rather than artificially structured layered systems to reduce lattice thermal conductivity.
Engineering of nanoscale structures is a requisite for controlling the electrical and thermal transport in solids, in particular for thermoelectric applications.
Engineering of nanoscale structures is a requisite for controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require a conflicting combination ...of low thermal conductivity and low electrical resistivity. We report the thermoelectric properties of spark plasma sintered Magneli phases WO sub(2.90) and WO sub(2.722). The crystallographic shear planes, which are a typical feature of the crystal structures of Magneli-type metal oxides, lead to a remarkably low thermal conductivity for WO sub(2.90). The figures of merit (ZT = 0.13 at 1100 K for WO sub(2.90) and 0.07 at 1100 K for WO sub(2.722)) are relatively high for tungsten-oxygen compounds and metal oxides in general. The electrical resistivity of WO sub(2.722) shows a metallic behaviour with temperature, while WO sub(2.90) has the characteristics of a heavily doped semiconductor. The low thermopower of 80 mu V K super(-1) at 1100 K for WO sub(2.90) is attributed to its high charge carrier concentration. The enhanced thermoelectric performance for WO sub(2.90) compared to WO sub(2.722) originates from its much lower thermal conductivity, due to the presence of crystallographic shear and dislocations in the crystal structure. Our study is a proof of principle for the development of efficient and low-cost thermoelectric materials based on the use of intrinsically nanostructured materials rather than artificially structured layered systems to reduce lattice thermal conductivity.
High energy-density lithium ion batteries (LIBs) are in demand for portable electronic devices and electrical vehicles. Since the energy density of these batteries relies heavily on the cathode ...material, a great deal of attention is being focused on developing alternative materials with a higher degree of Li utilization and specific energy density 1. In particular, layered Ni-rich oxides can deliver higher capacities at lower cost than the conventional LiCoO
2
(LCO). However, there are still several problems associated with their cycle life, thermal stability, and safety, which need to be solved 2. In addition, these drawbacks increase with increasing Ni amount, and motivate major research efforts to understand, mitigate and overcome these effects.
In stoichiometric layered lithium metal oxides, every vacant tetrahedral site is coordinated by either 3 lithium ions and 1 transition-metal (TM) ion, or 1 lithium ion and 3 TM ions. Effectively, only in the first case at least two Li sites are connected and can therefore sustain lithium migration. Hence, for each Li diffusion channel in the layered structure, exactly one gate site is a TM site, while the second one is a lithium site 3. The barrier for lithium migration through such a 1-TM channel is correlated to the TM valence and the areal lithium-TM separation. The latter varies with the width of the Li layer (the distance between TM-O slabs), constraining the degree of local relaxation for the TM when lithium enters the activated state 4. Nevertheless, the Li slab distance highly varies during discharge-charge processes and leads to cell volume fluctuation which is considered a potential source of electrode degradation, as it could favor the formation of microcracks 5. Moreover, this fluctuation increases with increasing Ni amount.
One promising approach to control the Li slab distance in high Ni materials is anionic substitution 6. In this work, the effect of N and F dopants is evaluated and a correlation between structural parameters and electrochemical performance was established. Moreover, the effect of N and F can be restricted to the materials surface. The stabilization of surfaces in high Ni materials is a fundamental challenge in order to control the aging processes of these materials.
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