Decouplingthe Electrical and Thermal Transport Propertiesin Ni-Composited La_3–<i>x</i>Te₄ Thermoelectrics

With excellent high-temperature thermoelectric performance, La_3–<i>x</i>Te₄ materials are considered leading candidates for the next generation of radioisotope thermoelectric generators. Despite this, conventional optimization strategies, such as element doping, have shown only a marginal improvement in their properties. To address this challenge, this study reports a series of Ni-composited La_2.74Te₄ materials incorporating uniformly distributed, fine Ni particles generated from NiTe_<i>x</i> precursors. These polydisperse nickel particles, with sizes ranging from the nano- to microscale, effectively decouple electrical and thermal transport properties. This decoupling reduces electrical resistivity while simultaneously suppressing the lattice thermal conductivity through phonon scattering, ultimately leading to substantially enhanced thermoelectric performance. As a result, an optimized composite with 13 vol % Ni yielded a record-high thermoelectric figure of merit (<i>zT</i>) of 1.6 at 1073 K, alongside an impressive average <i>zT</i> value of 1.1 across the 600–1100 K range. In addition, these Ni-composited La_2.74Te₄ materials also demonstrate superior oxygen resistance and enhanced fracture toughness, underscoring their potential as robust, high-performance candidates for high-temperature thermoelectric power generation applications.