Microstructure and thermoelectric properties of La-doped SrTiO3/TiO2 eutectic crystals grown by Micro-Pulling-Down method

La-doped SrTiO3/TiO2 (La:STO/TO) eutectic crystals were grown by a micro-pulling-down method at various growth rates to control the eutectic morphology and thermoelectric properties. The La:STO/TO eutectic crystals were composed of a TiO2 (TO) rod phase in the SrTiO3 (STO) matrix phase for all growth rates. The diameter of the TO rod phase systematically decreased as the growth rate was increased, according to the Jackson-Hunt model, and the diameter reached approximately 1 mu m at a growth rate of 1 mm/min. The La:STO/TO eutectic crystal exhibited a lower thermal conductivity than the Nb:STO single crystal, owing to the decrease in the lattice thermal conductivity by phonon scattering at boundaries in the eutectic morphology. The figures of merit, ZTs, of the La:STO/TO eutectic crystals grown at 0.02 and 0.5 mm/min growth rates were 0.015 and 0.025, respectively. The faster growth rate led to an increased ZT, owing to the decrease in electrical resistivity.

Automated summary

By controlling the growth rate, the morphology and thermoelectric properties of La:STO/TO eutectic crystals can be adjusted, with faster growth rates leading to higher figures of merit ZT.