Here we report the thermoelectric properties of NbCoSn-based n-type half-Heuslers (HHs) that were obtained through arc melting, ball milling, and hot pressing process. With 10% Sb substitution at the Sn site, we obtained enhanced n-type properties with a maximum power factor reaching ∼35 μW cm⁻¹ K⁻² and figure of merit (ZT) value ∼0.6 in NbCoSn_0.9Sb_0.1. The ZT is doubled compared to the previous report. In addition, the specific power cost ($ W⁻¹) is decreased by ∼68% comparing to HfNiSn-based n-type HH because of the elimination of Hf.

Chromium-doped TiO2 pigments were synthesized via a solid-state reaction method and studied with X-ray diffraction, SEM, XPS, and UV-VIS-NIR reflectance spectroscopy. The incorporation of Cr3+ accelerates the transition from the anatase phase to the rutile phase and compresses the crystal lattice. Moreover, the particle morphology, energy gap, and reflectance spectrum of Cr-doped TiO2 pigments is affected by the crystal structure and doping concentration. For the rutile samples, some of the Cr3+ ions are oxidized to Cr4+ after sintering at a high temperature, which leads to a strong near-infrared absorption band due to the 3A2 → 3 T1 electric dipole-allowed transitions of Cr4+. And the decrease of the band gap causes an obvious redshift of the optical absorption edges as the doping concentration increases. Thus, the VIS and near-infrared average reflectance of the rutile Ti1 − x Cr x O2 sample decrease by 60.2 and 58%, respectively, when the Cr content increases to x = 0.0375. Meanwhile, the color changes to black brown. However, for the anatase Ti1 − x Cr x O2 pigments, only the VIS reflection spectrum is inhibited by forming some characteristic visible light absorption peaks of Cr3+. The morphology, band gap, and NIR reflectance are not significantly affected. Finally, a Cr-doped anatase TiO2 pigment with a brownish-yellow color and 90% near-infrared reflectance can be obtained.

Recently, we found a new n-type thermoelectric half-Heusler NbCoSb with a valence electron count of 19, different from the usual 18. In this paper, we focus on the effect of partial substitution of Nb by isoelectronic elements V and Ta on the reduction of the thermal conductivity of Nb_(1−x)/2V_(1−x)/2Ta_xCoSb. We found that the isoelectronic elements V and Ta for partial substitution of Nb can dramatically decrease the thermal conductivity from 7.0 W m⁻¹ K⁻¹ to 3.3 W m⁻¹ K⁻¹ at room temperature for Nb_0.44V_0.44Ta_0.12CoSb, but unfortunately a large power factor decrease also occurred. Consequently, a peak ZT of ∼0.5 is achieved at 700 °C for Nb_0.44V_0.44Ta_0.12CoSb, which is about 25% higher than the ∼0.4 reported earlier for NbCoSb.