Both electrical conductivity σ and Seebeck coefficient S are functions of carrier concentration being correlated with each other, and the value of power factor S²σ is generally limited to less than 0.01 W m⁻¹ K⁻². Here we report that, under the temperature gradient applied simultaneously to both parallel and perpendicular directions of measurement, a metallic copper selenide, Cu₂Se, shows two sign reversals and colossal values of S exceeding ±2 mV K⁻¹ in a narrow temperature range, 340 K < T < 400 K, where a structure phase transition takes place. The metallic behavior of σ possessing larger magnitude exceeding 600 S cm⁻¹ leads to a colossal value of S²σ = 2.3 W m^–1 K^–2. The small thermal conductivity less than 2 W m⁻¹ K⁻¹ results in a huge dimensionless figure of merit exceeding 400. This unusual behavior is brought about by the self-tuning carrier concentration effect in the low-temperature phase assisted by the high-temperature phase.

The bulk thermal rectifiers usable at a high temperature above 300 K were developed by making full use of the unusual electron thermal conductivity of icosahedral quasicrystals. The unusual electron thermal conductivity was caused by a synergy effect of quasiperiodicity and by a narrow pseudogap at the Fermi level. The rectification ratio, defined by TRR = [Formula: see text], reached vary large values exceeding 2.0. This significant thermal rectification would lead to new practical applications for the heat management.

The effect of SnO₂ addition (0, 1, 2, 4 wt.%) on thermoelectric properties of c-axis oriented Al-doped ZnO thin films (AZO) fabricated by pulsed laser deposition on silica and Al₂O₃ substrates was investigated. The best thermoelectric performance was obtained on the AZO + 2% SnO₂ thin film grown on silica, with a power factor (PF) of 211.8 μW/m·K² at 573 K and a room-temperature (300 K) thermal conductivity of 8.56 W/m·K. PF was of the same order of magnitude as the value reported for typical AZO bulk material at the same measurement conditions (340 μW/m·K²) while thermal conductivity κ was reduced about four times.