Effect of Y substitution on the La-based iron oxypnictide superconductor ${\text{LaFeAsO}}_{0.6}$ is studied. Replacement of ${\text{La}}^{3+}$ $\left(1.16\text{Å}\right)$ by smaller ${\text{Y}}^{3+}$ $\left(1.019\text{Å}\right)$ in a form of ${\text{La}}_{1-x}{\text{Y}}_x{\text{FeAsO}}_{0.6}$ results in the decrease in lattice parameters, which likely causes pressure effect into the system. Superconducting transition temperature $\left(T_c\right)$ increases monotonically with $x$, eventually up to 43.1 K for $x=0.5$. This $T_c$ is comparable to the highest $T_c$ reported for Y-free F-doped ${\text{LaFeAsO}}_{1-x}{\text{F}}_x$ under high pressure. The present results provide an alternative and much simpler way to achieve higher $T_c$ in the La-based oxypnictide superconductors.

• Received 24 September 2008

DOI:https://doi.org/10.1103/PhysRevB.78.172503