High‐performance thermoelectric materials require simultaneous reduction of thermal conductivity and electrical resistivity, among other criteria. Here it is shown that the introduction of Na2CO3 into the melt‐route fabrication process for the well‐known thermoelectric Cu2Se has a beneficial and surprisingly strong effect. There is a significant enhancement in electrical conductivity which density functional theory calculations suggest may be due to the effect of Na and O doping in the Cu2Se matrix. There is also a 34% reduction in thermal conductivity which is likely due to a high density of defects causing scattering of phonons. Overall, however, there is only relatively a small change in Seebeck coefficient. A higher power factor of 12.6 µW cm−1 K−2 is achieved versus 8.8 µW cm−1 K−2 for standard Cu2Se. A very high value of zT of 2.3 is obtained at 804 K versus 1.1 for standard Cu2Se.

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This Data-in-brief article includes datasets of electron microscopy, polarised neutron reflectometry and magnetometry for ultra-small cobalt particles formed in titania thin films via ion beam synthesis. Raw data for polarised neutron reflectometry, magnetometry and the particle size distribution are included and made available on a public repository. Additional elemental maps from scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) are also presented. Data were obtained using the following types of equipment: the NREX and PLATYPUS polarised neutron reflectometers; a Quantum Design Physical Property Measurement System (14 T); a JEOL JSM-6490LV SEM, and a JEOL ARM-200F scanning transmission electron microscope (STEM). The data is provided as supporting evidence for the article in Applied Surface Science (A. Bake et al. , Appl. Surf. Sci., vol. 570, p. 151068, 2021, DOI 10.1016/j.apsusc.2021.151068 ), where a full discussion is given. The additional supplementary reflectometry and modelling datasets are intended to assist future scientific software development of advanced fitting algorithms for magnetization gradients in thin films.

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