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The intense research for efficient low-temperature thermoelectric materials motivates the exploration of innovative compounds and composite systems. This study examines the effects of integrating low-dimensional titanium trisulfide (TiS$_3$) into bulk tin-based halide perovskites (CsSnI$_3$) for use in thermoelectric applications. The addition of small amounts of two-dimensional titanium trisulfide (TiS$_3$) to bulk tin-based halide perovskites (CsSnI$_3$) significantly enhanced the structural stability of the composite material and suppressed oxidation processes. The CsSnI$_3$-TiS$_3$ composites demonstrated stabilization of temperature-dependent electrical properties (conductivity and Seebeck coefficient). This study provides valuable insights into the promising approach of using low-dimensional TiS3 as an additive to stabilize the thermoelectric performance of CsSnI$_3$., Comment: 11 pages, 4 figures

Ternary half Heusler alloys are under intense investigations recently towards achieving high thermoelectric figure-of-merit (ZT). Of particular interest is the ZrNiPb based half Heusler (HH) alloy where an optimal value of ZT = 0.7 at 773 K has been achieved by co-doping Sn and Bi at Pb site. In this work, we identify an excellent ZT of 1.3 in ZrNi1+xPb0.38Sn0.6Bi0.02 (x= 0.03, at 773 K) composite alloy. This is achieved by synergistic modulation of electronic as well as thermal properties via introduction of minor phase of full Heusler (FH) in the HH matrix through compositional tuning approach. These Ni-rich ZrNi1+xPb0.38Sn0.6Bi0.02 alloys were synthesized via Arc melting followed by consolidation via Spark Plasma Sintering (SPS). These alloys were characterized by XRD and SEM that shows formation of nanocomposites comprising of HH matrix phase and FH secondary minor phases. Enhancement in ZT is mainly attributed to a synchronized increase in power factor and about 25% decrease in its thermal conductivity. The thermoelectric compatibility factor (S) is also calculated for all samples. The theoretically calculated thermoelectric device efficiency of best performing sample ZrNi1.03Pb0.38Sn0.6Bi0.02 is estimated to be 13.6%. Our results imply that controlled fine tuning in HH compounds through compositional tuning approach would lead to novel off-stoichiometric HH phases with enhanced ZT value for efficient thermoelectric device fabrication.

We are witnessing a great transition towards a society powered by renewable energies to meet the ever-stringent climate target. Hydrogen, as an energy carrier, will play a key role in building a climate-neutral society. Although liquid hydrogen is essential for hydrogen storage and transportation, liquefying hydrogen is costly with the conventional methods based on Joule-Thomas effect. As an emerging technology which is potentially more efficient, magnetocaloric hydrogen liquefaction is a "game-changer". In this work, we have investigated the rare-earth-based Laves phases ${\rm R}Al_2$ and ${\rm R}Ni_2$ for magnetocaloric hydrogen liquefaction. We have noticed an unaddressed feature that the magnetocaloric effect of second-order magnetocaloric materials can become "giant" near the hydrogen boiling point. This feature indicates strong correlations, down to the boiling point of hydrogen, among the three important quantities of the magnetocaloric effect: the maximum magnetic entropy change $\Delta S_{m}^{max}$, the maximum adiabatic temperature change $\Delta T_{ad}^{max}$, and the Curie temperature $T_C$. Via a comprehensive literature review, we interpret the correlations for a rare-earth intermetallic series as two trends: (1) $\Delta S_{m}^{max}$ increases with decreasing $T_C$; (2) $\Delta T_{ad}^{max}$ decreases near room temperature with decreasing $T_C$ but increases at cryogenic temperatures. Moreover, we have developed a mean-field approach to describe these two trends theoretically. The dependence of $\Delta S_{m}^{max}$ and $\Delta T_{ad}^{max}$ on $T_C$ revealed in this work helps us quickly anticipate the magnetocaloric performance of rare-earth-based compounds, guiding material design and accelerating the discoveries of magnetocaloric materials for hydrogen liquefaction.

Among layered oxygen-containing compounds, BiCuSeO is one of the most promising candidates for thermoelectric applications due to its intrinsically low thermal conductivity and good thermal stability. However, the rather poor electrical conductivity of pristine BiCuSeO hinders its potential. Further enhancement of the thermoelectric performance by single doping at Bi site is limited mainly due to dramatic decrease of carrier mobility. Thus, new strategies, such as dual doping or doping with variable-valence elements seem to be promising. Along with that, the development of a fast and scalable synthesis route is essential for the industrial-scale fabrication of thermoelectric materials. Hence, in this paper, Bi$_{1-x}$Sm$_{x}$CuSeO samples (0 $\leq$ $x$ $\leq$ 0.08) have been synthesized with a simple and scalable reactive sintering process. For comparison, Bi$_{1-x}$Sm$_{x}$CuSeO oxyselenides were also obtained by the conventional solid-state route. Our results highlight that, Sm for Bi substitution increases the electrical conductivity by 1.5 - 2 times and decreases the Seebeck coefficient by ~1.4 times at 873 K for both series. Overall, considering the increase of lattice thermal conductivity upon doping and not optimized power factor, the figure of merit $zT$ is reducing upon doping., Comment: 9 pages, 4 figures, 2 tables; Supplemental information: 19 pages, 12 figures, 6 tables

In this study, we demonstrate that introducing of rare-earth elements, $R$ = La or Pr, into the Bi-O charge reservoir layer of BiCuSeO leads to an increase of both, the charge carrier concentration and the effective mass. Although the charge carrier mobility slightly decreases upon Bi$^{3+}$ to $R^{3+}$ substitution, the electronic transport properties are significantly improved in a broad temperature range from 100 K to 800 K. In particular, the electrical resistivity decreases by two times, while the Seebeck coefficient drops from 323 ${\mu}$V K$^{-1}$ to 238 ${\mu}$V K$^{-1}$ at 800 K. Thus, a power factor of nearly 3 ${\mu}$W cm$^{-1}$ K$^{-2}$ is achieved for Bi$_{0.92}$La$_{0.08}$CuSeO sample at 800 K. Meanwhile, a noticeable decrease of the lattice thermal conductivity is observed for the substituted samples, which can be attributed to the enhanced point defect scattering mostly originated from atomic mass fluctuations between $R$ and Bi. Ultimately, a maximum $zT$ value of nearly 0.34 at 800 K is obtained for the Bi$_{0.92}$La$_{0.08}$CuSeO sample, which is ~30% higher than that of pristine BiCuSeO., Comment: 15 pages, 8 figures, 3 tables; Supplemental information: 18 pages, 15 figures, 2 tables

Half-Heusler compounds exhibit a remarkable variety of emergent properties such as heavy-fermion behaviour, unconventional superconductivity and magnetism. Several of these compounds have been predicted to host topologically non-trivial electronic structures. Remarkably, recent theoretical studies have indicated the possibility to induce non-trivial topological surface states in an otherwise trivial half-Heusler system by strain engineering. Here, using magneto-transport measurements and first principles DFT-based simulations, we demonstrate topological surface states on strained [110] oriented thin films of YPdBi grown on (100) MgO. These topological surface states arise in an otherwise trivial semi-metal purely driven by strain. Furthermore, we observe the onset of superconductivity in these strained films highlighting the possibility of engineering a topological superconducting state. Our results demonstrate the critical role played by strain in engineering novel topological states in thin film systems for developing next-generation spintronic devices., Comment: 20 pages, 5 Figures

Herein, we demonstrate that BiCuSeO compound can be formed in bulk directly from the raw materials through reactive spark plasma sintering (RSPS) followed by ball milling and a second short spark plasma sintering step. Compared to BiCuSeO samples obtained by a conventional solid-state reaction, the electrical transport properties of the RSPS bulk were moderately affected by the sintering technique, while the lattice thermal conductivity was almost unaffected, and the figure of merit zT attained a value at 773 K comparable to state-of-the-art BiCuSeO. The results indicate a new scalable method for the preparation of oxyselenides., Comment: 7 pages, 4 figures, and 1 table | Supplementary information: 9 pages, 9 figures, and 1 table

We report on the direct ultrafast synthesis of Pb-doped BiCuSeO oxyselenides by high-energy ball milling. We show that, contrary to the mechanical alloying sintering routes used in the previous reports which require 7 - 13 hours to fabricate the BiCuSeO phase in powder form, this synthesis technique enables us to obtain pure phase materials at room temperature under air with milling time less than 60 minutes.

In this work we demonstrate that the polycrystalline ribbons of (Ni48Co6)Mn26Al20 with B2 structure at room temperature show a magnetic behavior with competing magnetic exchange interactions leading to frozen disorders at low temperatures. It is established that by considering the presence of both antiferromagnetic and ferromagnetic sublattices, we can explain the observed magnetic behavior including the metamagnetic transition observed in these samples. From the Arrott plots, the N\'eel temperature of (Ni48Co6)Mn26Al20 is deduced to be ~170 K and the broad ferro to para like magnetic phase transition is observed at ~ 200 K. Based on N\'eel theory, a cluster model is used to explain the presence of ferromagnetic and anti-ferromagnetic clusters in the studied ribbons. Formation of ferromagnetic clusters can be understood in terms of positive exchange interactions among the Mn atoms that are neighboring to Co atoms which are located on the Ni sites., Comment: 19 pages, 5 figures