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Abstract While ∼30% of materials are reported to be topological, topological insulators are rare. Magnetic topological insulators (MTI) are even harder to find. Identifying crystallographic features that can host the coexistence of a topological insulating phase with magnetic order is vital for finding intrinsic MTI materials. Thus far, most materials that are investigated for the determination of an MTI are some combination of known topological insulators with a magnetic ion such as MnBi₂Te₄. Motivated by the recent success of EuIn₂As₂, the role of chemical pressure on topologically trivial insulator is investigated, Eu₅In₂Sb₆via Ga substitution. Eu₅Ga₂Sb₆is predicted to be topological but is synthetically difficult to stabilize. The intermediate compositions between Eu₅In₂Sb₆and Eu₅Ga₂Sb₆are observed through theoretical works to explore a topological phase transition and band inversion mechanism. The band inversion mechanism is attributed to changes in Eu–Sb hybridization as Ga is substituted for In due to chemical pressure. Eu₅In_4/3Ga_2/3Sb₆is also synthesized, the highest Ga concentration in Eu₅In_2‐xGa_xSb₆, and report the thermodynamic, magnetic, transport, and Hall properties. Overall, the work paints a picture of a possible MTI via band engineering and explains why Eu‐based Zintl compounds are suitable for the co‐existence of magnetism and topology. 

Accurate density functional theory calculations of the interrelated properties of thermoelectric materials entail high computational cost, especially as crystal structures increase in complexity and size. New methods involving ab initio scattering and transport (AMSET) and compressive sensing lattice dynamics are used to compute the transport properties of quaternary CaAl 2 Si 2 -type rare-earth phosphides RECuZnP 2 (RE = Pr, Nd, Er), which were identified to be promising thermoelectrics from high-throughput screening of 20 000 disordered compounds. Experimental measurements of the transport properties agree well with the computed values. Compounds with stiff bulk moduli (>80 GPa) and high speeds of sound (>3500 m s −1 ) such as RECuZnP 2 are typically dismissed as thermoelectric materials because they are expected to exhibit high lattice thermal conductivity. However, RECuZnP 2 exhibits not only low electrical resistivity, but also low lattice thermal conductivity (∼1 W m −1 K −1 ). Contrary to prior assumptions, polar-optical phonon scattering was revealed by AMSET to be the primary mechanism limiting the electronic mobility of these compounds, raising questions about existing assumptions of scattering mechanisms in this class of thermoelectric materials. The resulting thermoelectric performance ( zT of 0.5 for ErCuZnP 2 at 800 K) is among the best observed in phosphides and can likely be improved with further optimization. 

The Zintl compound Eu 2 ZnSb 2 was recently shown to have a promising thermoelectric figure of merit, zT ∼ 1 at 823 K, due to its low lattice thermal conductivity and high electronic mobility. In the current study, we show that further increases to the electronic mobility and simultaneous reductions to the lattice thermal conductivity can be achieved by isovalent alloying with Bi on the Sb site in the Eu 2 ZnSb 2−x Bi x series ( x = 0, 0.25, 1, 2). Upon alloying with Bi, the effective mass decreases and the mobility linearly increases, showing no signs of reduction due to alloy scattering. Analysis of the pair distribution functions obtained from synchrotron X-ray diffraction revealed significant local structural distortions caused by the half-occupied Zn site in this structure type. It is all the more surprising, therefore, to find that Eu 2 ZnBi 2 possesses high electronic mobility (∼100 cm 2 V −1 s −1 ) comparable to that of AM 2 X 2 Zintl compounds. The enormous degree of disorder in this series gives rise to exceptionally low lattice thermal conductivity, which is further reduced by Bi substitution due to the decreased speed of sound. Increasing the Bi content was also found to decrease the band gap while increasing the carrier concentration by two orders of magnitude. Applying a single parabolic band model suggests that Bi-rich compositions of Eu 2 ZnSb 2−x Bi x have the potential for significantly improved zT ; however, further optimization is necessary through reduction of the carrier concentration to realize high zT . 

Rare-earth (RE) tellurides have been studied extensively for use in high-temperature thermoelectric applications. Specifically, lanthanum and praseodymium-based compounds with the Th3P4 structure type have demonstrated dimensionless thermoelectric figures of merit (zT) up to 1.7 at 1200 K. Scandium, while not part of the lanthanide series, is considered a RE element due to its chemical similarity. However, little is known about the thermoelectric properties of the tellurides of scandium. Here, we synthesized scandium sesquitelluride (Sc2Te3) using a mechanochemical approach and formed sintered compacts through spark plasma sintering (SPS). Temperature-dependent thermoelectric properties were measured from 300–1100 K. Sc2Te3 exhibited a peak zT = 0.3 over the broad range of 500–750 K due to an appreciable power factor and low-lattice thermal conductivity in the mid-temperature range. 

A M 2 X 2 compounds that crystallize in the CaAl 2 Si 2 structure type have emerged as a promising class of n- and p-type thermoelectric materials. Alloying on the cation (A) site is a frequently used approach to optimize the thermoelectric transport properties of A M 2 X 2 compounds, and complete solid solubility has been reported for many combinations of cations. In the present study, we investigate the phase stability of the AMg 2 Sb 2 system with mixed occupancy of Mg, Ca, Sr, or Ba on the cation (A) site. We show that the small ionic radius of Mg 2 + leads to limited solubility when alloyed with larger cations such as Sr or Ba. Phase separation observed in such cases indicates a eutectic-like phase diagram. By combining these results with prior alloying studies, we establish an upper limit for cation radius mismatch in A M 2 X 2 alloys to provide general guidance for future alloying and doping studies.