Peter Rogl

Thermodynamic modelling of the Nb–Sb system was performed by the CALPHAD method, based on SGTE data and on data from experimental studies in the literature combined with our new information obtained via DTA, EDX-EPMA, XPD and ab initio calculations.

Besides filled skutterudites with a high figure of merit, unfilled skutterudites also play an important role as thermoelectric materials; furthermore, they are easier to produce and do not need expensive rare earths as fillers. In the present review, thermoelectric properties (at 300 K and at the highest measured temperature) of more than 600 compositions from more than 230 publications between 1957 and 2025 were collected and evaluated. In various figures, the dependence of the peak ZT on the electrical resistivity, Seebeck coefficient, the power factor and the thermal conductivity is displayed for (i) binary CoSb₃, for (ii) CoSb₃ substituted at the Co-site, for (iii) substitution at the Sb-site or at both sites as well as for (iv) unfilled skutterudites without Co or Sb or Co and Sb. In most cases, the peak ZT equals the ZT at the highest measured temperature. Thermoelectric data are listed (i) to comply with the periodic chart and publishing year as well as (ii) in the form of a graphical overview of all discussed skutterudites. In this respect, this review will support the search for the ideal TE material for practical use.

The integration of artificial intelligence and machine learning is transforming the landscape of materials discovery, facilitating unprecedented acceleration in the exploration of vast chemical spaces and the prediction of material properties.

Thermoelectric (TE) technology uses the Seebeck effect to directly convert heat into electricity or vice versa. Amongst its advantages are the lack of moving parts, reliability, absence of refrigerant gasses and scalability. To date, commercial progress has been limited due to relatively low conversion efficiencies and high costs. However, with increasing energy costs, the advent of the Internet of Things and its needs to power many sensors, and the need for thermal management in electronics, there is plenty of reason to be optimistic about the future of TE energy conversion. Beyond using abundant elements, sustainability has so far not been a major consideration in the development of TE technology, with its understandable emphasis on improving performance. However, sustainability aspects, including eco-friendly processing, resource efficient module fabrication, ensuring a long working life and end of life recycling should all be major considerations from the outset. This roadmap aims to provide an overview of current efforts moving towards sustainable TEs as well as guidance for future work. In terms of organization, the roadmap contains cross-cutting sections on aspects of sustainability and sections focused on the major TE materials. It can be read front to back or focusing on chapters of particular interest. We hope that this roadmap will stimulate new research, leading to the early adoption of sustainability concepts, beyond using abundant elements, in the development of large-scale TE technology.

The integration of artificial intelligence and machine learning is rapidly transforming the landscape of materials discovery, facilitating unprecedented acceleration in the exploration of vast chemical spaces and the prediction of material properties. However, the adoption of these advanced techniques has not been uniform across all subfields of materials science; thermoelectrics, for instance, has experienced a relatively slower penetration. This lag can be attributed to several inherent challenges, including the physical complexity of thermoelectric phenomena, the scarcity and reliability issues of available data, and limitations concerning the applicability of general models. To address these challenges, in this work, we have developed a machine learning model, based on neural networks, specifically for the accurate prediction of the thermoelectric figure of merit (zT) in skutterudites. This model demonstrates high accuracy, with prediction errors approaching the range of experimental uncertainties reported for zT measurements. Furthermore, it offers the crucial capability of extracting design rules grounded in the underlying physics and chemistry of these materials, providing valuable insights for optimization. Most importantly, our model is applicable for the high-throughput screening of extensive chemical spaces, facilitating the efficient discovery of novel and high-performance thermoelectric materials.

A novel ternary boride, NiPtB_2-x (x = 0.5), was obtained by argon-arc melting of the elements followed by annealing at 750 °C. It exhibits a new structure type with the space group Imma (a = 2.9835(3) Å, b = 3.0470(3) Å, c = 15.3843(3) Å; Z = 4; single-crystal X-ray data) and displays distinct layers of condensed [BNi₆] and [BPt₆] (and [Pt₆]) trigonal prisms with mutually perpendicular axes. Atoms of Pt and Ni from adjacent layers interlink to form empty tetragonal pyramids and tetrahedra. Two boron atom positions form two orthogonal zigzag chains; however, one boron position exhibits a partial boron occupancy. Considering B-deficiency, the platinum boride substructure in NiPtB_2-x quantitatively corresponds to a trigonal prismatic slab in the Pt₂B structure, while the nickel boride partial structure is consistent with the CrB-type NiB binary. Cell parameters and atomic coordinates of NiPtB_2-x and Pt₂B were refined in the scope of generalized gradient approximation. Chemical bonding analysis by means of the electron localizability approach, supported by Bader charge analysis, reveals a strong electron contribution of Ni atoms for stabilization of the boron zigzag chains, wherein boron atoms are bonded covalently. Bonding within the platinum boride partial structures in the studied compounds varies depending on the atom coordination of boron: from covalent in both the NiPtB_2-x structure and trigonal prismatic slabs in Pt₂B to mixed metallic with covalent contributions in [BPt₆] octahedra in Pt₂B. Electrical resistivity measurements characterize NiPtB_2-x as a metal with no phase transitions in the temperature range from 2 to 300 K, in concord with electronic band structure calculations and specific heat measurements. The compound is characterized by a positive Hall coefficient at 20 K. This work unveils a new elemental space on realizing novel layered boride structural arrangements and provides a reference for future experiments.