That said, at lower charge-carrier concentrations our calculations predict that nanostructuring would improve the ZT. Figure shows the absolute difference in the ZT obtained by nanostructuring to both 10 nm (Figure ) and 20 nm (Figure ), which shows similar trends. Below carrier concentrations of 10 20 cm -3 , a slight increase in ZT is seen, with larger increases at higher temperatures. On the other hand, the scattering introduced by grain boundaries at higher charge-carrier concentrations leads to a decrease in the power factor that is not compensated by the decrease in the thermal conductivity. We noted earlier that maximising the ZT requires doping levels that are close to the limit of what is routinely achievable in experiments -we therefore conclude that the utility of nanostructuring for optimising the ZT of this material depends on the doping levels achievable in experiments. In conclusion, we have demonstrated using state-of-the-art DFT calculations that Y 2 Ti 2 O 5 S 2 is a promising high-and intermediate-temperature n-type thermoelectric with a predicted maximum in-plane ZT of 1.18 at 1000 K, which is obtained for a carrier concentration of 2.37 × 10 20 cm -3 .