Efforts to tune the bulk physical properties of concrete are hindered by a lack of knowledge related to the atomiclevel structure and growth of calcium silicate hydrate phases, which form about 50-60% by volume of cement paste. Here we describe the first synthesis of compositionally uniform calcium silicate hydrate phases with Ca:Si ratios tunable between 1.0 and 2.0. The calcium silicate hydrate synthesized here does not contain a secondary Ca(OH)2 phase, even in samples with Ca:Si ratios above 1.6, which is unprecedented for synthetic calcium silicate hydrate systems. We then solve the atomic-level three-dimensional structure of these materials using dynamic nuclear polarization enhanced 1 H and 29 Si nuclear magnetic resonance experiments in combination with atomistic simulations and density functional theory chemical shift calculations. We discover that bridging interlayer calcium ions are the defining structural characteristic of single-phase cementitious calcium silicate hydrate, inducing the strong hydrogen bonding that is responsible for stabilizing the structure at high Ca:Si ratios.

We report a remarkably high and stable thermoelectric zT ∼ 2 by manipulating the electronic bands in hybrid flash-SPSed Ga–Sb codoped GeTe.

GeTe, which undergoes phase transition between low symmetric rhombohedral to high symmetric cubic phase between 550 – 700 K (depending on the dopant and composition) and its alloys have widely...

Flexible, large-area, and low-cost thermal sensing network with high spatial and temporal resolution are of profound importance in addressing the increasing needs for industrial processing, medical diagnosis, and military defense. Here, a thermoelectric fiber is fabricated by thermally co-drawing of a macroscopic preform containing semiconducting glass core and polymer cladding to deliver thermal sensor functionalities at fiber-optic length scales, flexibility, and uniformity. The resulting thermoelectric fiber sensor operates in a wide temperature range with high thermal detection sensitivity and accuracy, while offering ultra-flexibility with the 2 bending curvature radius below 2.5 mm. Additionally, a single thermoelectric fiber can either sense the spot temperature variation or locate the heat/cold spot on the fiber. As a proof-ofconcept, a two-dimensional 3×3 fiber array is woven into a textile to simultaneously detect the temperature distribution and the position of heat/cold source with the spatial resolution of millimeter. Achieving this may lead to the realization of large-area, flexible and wearable temperature sensing fabrics for wearable electronics and advanced artificial intelligence applications.

A comprehensive study on the thermoelectric effect of Ag substitution in GeTe solid solutions, a congenital base for high efficient TAGS-m [(GeTe) m (AgSbTe 2 ) 100-m ] thermoelectric materials, was performed. First-principles calculations were carried out to probe the changes arising from doping on the electronic band structure of GeTe, which exhibits a rhombohedral (r) structure at temperatures lower than 700 K. Aliovalent Ag substitution in GeTe increases the hole concentration and decreases the thermoelectric figure of merit (zT) due to the reduction of the Seebeck coefficient, which is ascribed mainly to the lowering of the Fermi level together with the loss of band degeneracy. Band structure and effective mass calculations of these doped materials also point to a soaring contribution from several hole pockets in the valence band. First-principles calculations carried out with two other group-11 transition metals (Cu, Au) reveal that silver substitution has the lowest impact on the thermopower of r- Page 1 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 GeTe. A mean zT of ∼0.85 at 773 K is achieved for Ge 1-x Ag x Te (x ≤ 0.04) solid solutions. The study highlights the limits in doping just a coinage metal to GeTe and recapitulates the need for pair substitution to enhance the thermoelectric properties of GeTe-based solid-state solutions.

Most of the best known SnTe‐based materials exhibit an attractive thermoelectric figure of merit (zT) only at the high‐temperature regime, but their performance at the low‐mid temperature ranges is quite uninspiring, and this discordance necessitates a large temperature gradient (∆T ≥ 550 K) to effectuate a reasonable efficiency, η. Here, the transition elements, Ti and Zr, that have not been used in the past are tried as dopants for SnTe and an enhanced device/average zT and/or η are reported with a lower ∆T ≈ 400 K and without the requisite for a stupendous peak/maximum zT. This notable performance emanates from—i) improved weighted mobility by optimally balancing between effective mass, carrier concentration, and mobility, ii) coupling of charge carriers with magnetic entropy, and the paramount factor being the iii) weakening of the chemical bonds (lattice softening). The thermal damping caused by lattice softening affects the phonon group velocity and the elastic properties, and the resultant increase in the degree of anharmonicity and the high density of internal strain‐fields, along with the phonon scattering effects, play an active role in tuning the overall thermoelectric performance. This work also excavates/opens up the discussion of applying the Heikes’ equation to qualitatively compare the trend of charge carriers for a given thermoelectric material system.

The quaternary AgPb18SbTe20 compound (abbreviated as LAST) is a prominent thermoelectric material with good performance. Endotaxially embedded nanoscale Ag-rich precipitates contribute significantly to decreased lattice thermal conductivity (latt) in LAST alloys. In this work, Ag in LAST alloys was completely replaced by the more economically available Cu. Herein, we conscientiously investigated the different routes of synthesizing CuPb18SbTe20 after vacuum-sealed tube melt processing, including: (i) slow cooling of the melt; (ii) quenching and annealing; (iii) consolidation by spark plasma sintering (SPS); and also by the state-of-the-art (iv) Flash-SPS. Irrespective of the method of synthesis, the electrical (σ) and thermal (tot) conductivities of CuPb18SbTe20 samples were akin to that of LAST alloys. Both the flash-SPSed and the slow cooled CuPb18SbTe20 samples with nanoscale dislocations and Cu-rich nanoprecipitates exhibited an ultra-low latt  0.58 W/mK at 723 K, comparable with that its Ag counterpart, regardless of differences in their size of the precipitates, type of precipitate-matrix interfaces and other nanoscopic architectures.The sample processed by flash sintering manifested higher figure of merit (zT  0.9 at 723 K), due to better optimization and trade-off between the transport properties by decreasing the carrier concentration and latt without degrading the carrier mobility. In spite of their comparable σ and tot, the zT of the Cu samples were low compared to the Ag samples due to their contrasting thermopower values. First-principles calculations attribute this variation in Seebeck to the dwindling of the energy gap (from 0.1 eV to 0.02 eV) between the valence and conduction bands in MPb18SbTe20 (M = Cu or Ag), when Cu replaces Ag. Materials and Methods ReagentsPb (Strem Chemicals, 99.999%), Sb (Alfa Aesar, 99.999%), Cu (Alfa Aesar, 99.999%) and Te (JGI, 99.999%) were used for synthesis without any further purification. SynthesisIn this work, several different processing routes were investigated, however, the first step (synthesis) was common to all of the processing routes. Samples of CuPb18SbTe20 were synthesized using the vacuumsealed tube melt processing. Stoichiometric amounts of the starting elements of Cu, Pb, Sb and Te were introduced into a fused silica tube. The tube was prepared by cleaning with hydrofluoric (HF) acid and distilled water, then dried under vacuum. The ampoules were sealed under a vacuum of 10 -6 Torr, then placed in a rocking furnace and slowly heated to 1223 K over a period of 12 hours, then held at that temperature for 15 hours. Four different batches of samples were prepared, the first two were produced directly from the molten material, followed by: (i) cooling the melt to room temperature over a period of 18 hours (samples denoted as 'SS'); (ii) rapidly quenching the tube in water, followed by annealing at 973 K for 8 hours (denoted as 'MQ'). The other two batches used the material produced by method (i), which was crushed and milled. The powders were then ...

A mesoscale pathway of calcium–silicate–hydrate precipitation, leading to nanocrystallites packing nematically in anisotropic particles is quantitatively described for the first time.